## 1. Chomsky's Case against Skinner




The behaviorist psychologist B.F. Skinner was the first theorist to 
propose a fully fledged theory of language acquisition in his book, 
*Verbal Behavior* (Skinner 1957). His theory of learning was 
closely related to his theory of linguistic behavior itself. He 
argued that human linguistic behavior (that is, our own utterances 
and our responses to the utterances of others) is determined by two 
factors: (i) the current features of the environment impinging on the
speaker, and (ii) the speaker's history of reinforcement (i.e., the 
giving or withholding of rewards and/or punishments in response to 
previous linguistic behaviors). Eschewing talk of the mental as 
unscientific, Skinner argued that 'knowing' a language is
really just a matter of having a certain set of behavioral 
dispositions: dispositions to say (and do) appropriate things in 
response to the world and the utterances of others. Thus, knowing 
English is, in small part, a matter of being disposed to utter 
"Please close the door!" when one is cold as a result of 
a draught from an open door, and of being disposed (other things 
being equal) to utter "OK" and go shut a door in response
to someone else's utterance of that formula.




Given his view that knowing a language is just a matter of having a 
certain set of behavioral dispositions, Skinner believed that 
learning a language just amounts to acquiring that set of 
dispositions. He argued that this occurs through a process that he 
called *operant conditioning*. ('Operants' are 
behaviors that have no discernible law-like relation to particular 
environmental conditions or 'eliciting stimuli.' They are
to be contrasted with 'respondents,' which are reliable 
or reflex responses to particular stimuli. Thus, blinking when 
someone pokes at your eye is a respondent; episodes of infant 
babbling are operants.) Skinner held that most human verbal behaviors
are operants: they start off unconnected with any particular stimuli.
However, they can acquire connections to stimuli (or other behaviors)
as a result of conditioning. In conditioning, the behavior in 
question is made more (or in some paradigms less) likely to occur in 
response to a given environmental cue by the imposition of an 
appropriate 'schedule of reinforcement': rewards or 
punishments are given or withheld as the subject's response to the 
cue varies over time.




According to Skinner, language is learned when children's verbal 
operants are brought under the 'control' of environmental
conditions as a result of training by their caregivers. They are 
rewarded (by, e.g., parental approval) or punished (by, say, a 
failure of comprehension) for their various linguistic productions 
and as a result, their dispositions to verbal behavior gradually 
converge on those of the wider language community. Likewise, Skinner 
held, 'understanding' the utterances of others is a 
matter of being trained to perform appropriate behaviors in response 
to them: one understands 'Shut the door!' to the extent 
that one responds appropriately to that utterance.




In his famous review of Skinner's book, Chomsky (1959) effectively 
demolishes Skinner's theories of both language mastery and language 
learning. First, Chomsky argued, mastery of a language is not merely 
a matter of having one's verbal behaviors 'controlled' by
various elements of the environment, including others' utterances. 
For language use is (i) stimulus independent and (ii) historically 
unbound. Language use is *stimulus independent*: virtually any
words can be spoken in response to any environmental stimulus, 
depending on one's state of mind. Language use is also 
*historically unbound*: what we say is not determined by our 
history of reinforcement, as is clear from the fact that we can and 
do say things that we have not been trained to say.




The same points apply to comprehension. We can understand sentences 
we have never heard before, even when they are spoken in odd or 
unexpected situations. And how we react to the utterances of others 
is again dependent largely on our state of mind at the time, rather 
than any past history of training. There are linguistic conventions 
in abundance, to be sure, but as Chomsky rightly pointed out, human 
'verbal behavior' is quite disanalogous to a pigeon's 
disk-pecking or a rat's maze-running.. Mastery of language is not a 
matter of having a bunch of mere behavioral dispositions. Instead, it
involves a wealth of pragmatic, semantic and syntactic knowledge. 
What we say in a given circumstance, and how we respond to what 
others say, is the result of a complex interaction between our 
history, our beliefs about our current situation, our desires, 
*and our knowledge of how our language works.* Skinner's first
big mistake, then, was in failing to recognize that language mastery 
involves knowledge (or, as Chomsky later called it 
'cognizance') of linguistic rules and conventions.




His second big mistake was related to this one: he failed to 
recognize that acquiring mastery of a language is not a matter of 
being trained what to say. It's simply false, says Chomsky, that 
"a careful arrangement of contingencies of reinforcement by the
verbal community is a necessary condition of language 
learning." (1959:39) First, children learning language do not 
appear to be being 'conditioned' at all! Explicit 
training (such as a dog receives when learning to bark on command) is
simply not a feature of language acquisition. It's only comparatively
rarely that parents correct (or explicitly reward) their children's 
linguistic sorties; children learn much of what they know about 
language from watching TV or passively listening to adults; immigrant
children learn a second language to native speaker fluency in the 
school playground; and even very young children are capable of 
linguistic innovation, saying things undreamt of by their parents. As
Chomsky concludes: "It is simply not true that children can 
learn language only through 'meticulous care' on the part
of adults who shape their verbal repertoire through careful 
differential reinforcement." (1959:42)




Secondly, Chomsky argued -- and here we see his first invocation
of the famous 'poverty of the stimulus' argument, to be 
discussed in more detail in SS2.2 below -- it is unclear 
that conditioning could *even in principle* give rise to a set
of dispositions rich enough to generate the full range of a person's 
linguistic behavior. In order, for example, to acquire the 
appropriate set of dispositions concerning the word *car*, one
would have to be trained on vast numbers of sentences containing that
word: one would have to hear *car* in object position and 
*car* in subject position; *car* modified by adjectives
and *car* unmodified; *car* embedded in opaque contexts
(e.g. in propositional attitude ascriptions) and *car* used 
transparently; and so on. But the 'primary linguistic 
data,' usually referred to as the '*pld'* 
and comprising the set of sentences to which a child is exposed 
during language learning (plus any analysis performed by the child on
those sentences; see below), simply cannot be assumed to contain 
enough of these 'minimally differing sentences' to fully 
determine a person's dispositions with respect to that word. Instead,
Chomsky argued, what determines one's dispositions to use 
*car* is one's knowledge of that word's syntactic and semantic
properties (e.g., *car* is a noun referring to cars), together
with one's knowledge of how elements with those properties function 
in the language as a whole. So even if language mastery were (in 
part) a matter of having dispositions concerning *car*, the 
mechanism of conditioning would be unable to give rise to them. The 
training set to which children have access is simply too limited: it 
doesn't contain enough of the right sorts of exemplars.




In sum: Skinner was mistaken on all counts. Language mastery is not 
merely a matter of having a set of bare behavioral dispositions. 
Instead, it involves intricate and detailed knowledge of the 
properties of one's language. And language learning is not a matter 
of being trained what to say. Instead, children learn language just 
from hearing it spoken around them, and they learn it effortlessly, 
rapidly, and without much in the way of overt instruction.




These insights were to drive linguistic theorizing for the next fifty
years, and it's worth emphasizing just how radical and exciting they 
were at the time. First, the idea that explaining language use 
involves attributing *knowledge* to speakers flouted the 
prevailing behaviorist view that talking about mental states was 
unscientific because mental states are unobservable. It also raised 
several pressing empirical question that linguists are still 
debating. For example, what is the *content* of speakers' 
knowledge of 
 language?[3]
 What sorts of facts about language are represented in speakers' 
heads? And how does this knowledge actually function in the 
psychological processes of language production and comprehension: 
what are the *mechanisms* of language use?




Secondly, the idea that children learn language essentially on their 
own was a radical challenge to the prevailing behaviorist idea that 
all learning involves reinforcement. In addition, it made clear our 
need for a more 'cognitive' or 'mentalistic' 
conception of how language learning occurs, and vividly raised the 
question -- our focus in this article -- of what might be 
the *preconditions* for that process. As we will see in the 
next section, Chomsky was ready with a theory addressing each of 
these points.


## 2. Arguments for the Innateness of Language


### 2.1 What do Children Learn when they Learn Language?




At the same time as the behaviorist program in psychology was waning 
under pressure from Chomsky and others, linguists were abandoning 
what is known as 'American Structuralism' in the theory 
of syntax. Like the behaviorists, the structuralists (e.g., Harris, 
1951) refused to postulate irreducibly theoretical entities; they 
insisted that syntactic categories (such as 'noun phrase'
('NP') or 'verb phrase' ('VP'), 
etc.) be reducible to properties of actual utterances (collected in 
'corpora' -- lists of things people have said). In 
his landmark book, *Syntactic Structures* (1957), however, 
Chomsky argued that because corpora can contain only finitely many 
sentences, no attempt at reduction can succeed. Linguists need 
theoretical constructs that capture regularities going beyond the set
of actual utterances, and that allow them to predict the properties 
of novel utterances. But if the category NP, for instance, is to 
include noun phrases that haven't been uttered yet, the meaning of 
*noun phrase* can't be exhausted by what's in the corpus: the 
structuralists' positivistic strictures on theoretical kinds are 
misguided.




In addition, the structuralists had attempted to capture the 
syntactic properties of languages in terms of simple rewrite rules 
known as 'phrase structure rules.' Phrase structure rules
describe the internal syntactic structures of sentence types; 
interpreted as rewrite rules, they can be used to generate or 
construct sentences. Thus, the rule S - NP VP, for instance, 
says that a sentence symbol S can be rewritten as the symbol NP 
followed by the symbol VP, and tells you that a sentence consists of 
a noun phrase followed by a verb phrase. (This information can be 
represented via a tree-diagram, as in Fig. 1a, or by a phrasemarker 
(or labeled bracketing), as in Fig. 1b.)



> 
> 
> 
> |  |  |
> | --- | --- |
> | S-NP-VP Tree | [[\_\_\_]NP[\_\_\_]VP]S |
> | (a) | (b) |
> 
> 
> 
> 
> Figure 1. Phrasemarkers representing a sentence as consisting of a 
> noun phrase and a verb phrase via (a) a tree diagram or (b) a labeled
> bracketing.
> 
> 
> 




Other rules, (such as NP - Det N, VP - V NP, Det - 
*a, the,* ..., etc., V- *hit, kiss*..., 
etc.; N - *boy, girl*,..., etc.) are subsequently 
applied, and (with still further rules not discussed here) allow for 
the generation of sentences such as *The boy kissed the girl, The 
girl hits the boy*, and so on. 




Chomsky argued (on technical grounds; see Chomsky 1957, ch.1) that 
grammars must be enriched with a second type of rule, known as 
'transformations.' Unlike phrase structure rules, 
transformations operate on whole sentences (or more strictly, their 
phrasemarkers); they allow for the generation of new sentences 
(/phrasemarkers) out of old ones. The *Passive* transformation
described in Chomsky 1957:112, for instance, specifies how to turn an
active sentence (/phrasemarker) into a passive one. Simplifying 
somewhat, you take an active phrasemarker of the form *NP -- 
Aux* -- *V -- NP*, like *Kate is biting 
Mark,* and rearrange its elements *x*1 -- 
*x*2 -- *x*3 -- 
*x*4 as follows: *x*4 -- 
*x*2 + *be* + *en* -- 
*x*3 + *by* -- *x*1 
to get *Mark bite* (+ *is* + *en*) *by 
Kate*. The parenthetical *+ en* and *+ is* invoke 
further operations on the verb *bite* that transform it into 
*is being bitten,* and ultimately *Kate is biting Mark*
is 'transformed' into *Mark is being bitten by 
Kate.*




Only a grammar containing both phrase structure and transformation 
rules, Chomsky argued, could generate a natural language -- 
'generate' in the sense that by stepwise application of 
the rules, one could in principle build up from scratch all and only 
the sentences that the language contains. Hence, Chomsky urged the 
development of generative grammars of this type.




Syntactic theory has now gone well beyond this early vision -- 
both phrase structure and transformation rules were abandoned in 
successive linguistic revolutions wrought by Chomsky and his students
and colleagues (see Newmeyer 1986, 1997 for a history of generative 
linguistics).




But what has not changed -- and what is important for our 
purposes -- is that in every version of the grammar of (say) 
English, the rules governing the syntactic structure of sentences and
phrases are stated in terms of syntactic categories that are highly 
abstracted from the properties of utterances that are accessible to 
experience. As an example of this, consider the notion of a 
*trace.* Traces are symbols that appear in phrasemarkers and 
mark the path of an element as it is moved from one position to 
another at various stages of a sentence's derivation, as in (1), 
where ti markes the NP *Jacob*'s position at an 
earlier stage in the derivation.


1. Jacobi seems [ti to have vanished]




But while traces are vital to the statement of many syntactic rules 
and regularities, they are 'empty categories' -- 
they are not audible in the sentence as spoken. (See Chomsky 1981 
and Lasnik and Uriagereka 1986 for more on traces and other empty 
categories.) Traces (and other similarly abstract properties of 
languages) thus raise a question for the theory of language 
acquisition. For if, as Chomsky maintains, mastery of language 
involves knowledge of rules stated in terms of sentences' syntactic 
properties, and if those properties are not so to speak 
'present' in the data, but are rather highly abstract and
'unobservable,' then it becomes hard to see how children 
could possibly acquire knowledge of the rules concerning them. As a 
consequence, children's feat in learning a language appears 
miraculous: how could a child learn the myriad rules governing 
linguistic expression given only her exposure to the sentences spoken
around 
 her?[4]





In response to this question, most 20th century theorists followed 
Chomsky in holding that language acquisition could not occur unless 
much of the knowledge eventually attained were innate or inborn. The 
gap between what speaker-hearers know about language (its grammar, 
among other things) and the data they have access to during learning 
(the *pld*) is just too broad to be bridged by any process of 
learning alone. It follows that since children patently do learn 
language, they are not linguistic 'blank slates.' 
Instead, Chomsky and his followers maintained, human children are 
born knowing the 'Universal Grammar' or 'UG,'
a theory describing the most fundamental properties of all natural 
languages (e.g., the facts that elements leave traces behind when 
they move, and that their movements are constrained in various ways).
Learning a particular language thus becomes the comparatively simple 
matter of elaborating upon this antecedently possessed knowledge, and
hence appears a much more tractable task for young children to 
attempt.




Over the years, two conceptions of the innate contribution to 
language learning and its elaboration during the learning process 
have been proposed. In earlier writings (e.g., Chomsky 1965), Chomsky
saw learning a language as basically a matter of formulating and 
testing hypotheses about its grammar -- unconsciously, of 
course. He argued that in order to acquire the correct grammar, the 
child must innately know a "a linguistic theory that specifies 
the form of the grammar of a possible human language" (1965:25)
-- she must know UG in other words. He saw this knowledge as 
being embodied in a suite of innate linguistic abilities, concepts, 
and constraints on the kinds of grammatical rules learners can 
propose for testing. On this view (1965:30-31), the inborn UG 
includes (i) a way of analyzing and representing the incoming 
linguistic data; (ii) a set of linguistic concepts with which to 
state grammatical hypotheses; (iii) a way of telling how the data 
bear on those hypotheses (an 'evaluation metric'); and 
(iv) a very restrictive set of constraints on the hypotheses that are
available for consideration. (i) through (iv) constitute the 
'initial state' of the language faculty, and the child 
arrives at the final state (knowledge of her language) by performing 
what is basically a kind of scientific inquiry into its nature.




By the 1980's, a less intellectualized conception of how language is 
acquired began to supplant the hypothesis-testing model. Whereas the 
early model saw the child as a 'little scientist,' 
actively (if unconsciously) figuring out the rules of grammar, the 
new 'parameter-setting' model conceived language 
acquisition as a kind of growth or maturation; language acquisition 
is something that happens to you, not something you do. The innate UG
was no longer viewed as a set of tools for inference; rather, it was 
conceived as a highly articulated set of representations
of actual grammatical principles. Of course, since not everyone ends 
up speaking the same language, these innate representations must 
allow for some variation. This is achieved in this model *via*
the notion of a 'parameter': some of the innately 
represented grammatical principles contain variables that may take 
one of a certain (highly restricted) range of values. These different
'parameter settings' are determined by the child's 
linguistic experience, and result in the acquisition of different 
languages. Thus, Chomsky (1988:61-62) compared the learner to a 
switchbox: just as a switchbox's circuitry is all in place but for 
some switches that need to be flicked to one position or another, the
learner's knowledge of language is basically all in place, but for 
some linguistic 'switches' that are set by linguistic 
experience.




To illustrate how parameter setting works, consider a simplified 
example (discussed in more detail in Chomsky 1990:644-45). All 
languages require that sentences have subjects, but whereas some 
languages (like English) require that the subject be overt in the 
utterance, other languages (like Spanish) allow you to leave the 
subject out of the sentence when it is written or spoken. Thus, a 
Spanish speaker who wanted to say that he speaks Spanish could say 
*Hablo espanol* (leaving out the first personal pronoun
*yo*) without violating the rules of Spanish, whereas an 
English speaker wanting to express that thought could not say 
\**Speak Spanish* without violating the rules of English: to 
speak grammatically, he must say *I speak Spanish.* The 
parameter-setting model accommodates this sort of difference by 
proposing that there is a 'Null Subject Parameter,' which
is set differently in English and Spanish speakers: Spanish speakers 
set it to 'Subject Optional,' whereas in English 
speakers, it is set to 'Subject Obligatory.' How? One 
proposal is that the parameter is set by default to 'Subject 
Obligatory' and that hearing a subjectless sentence causes it 
to be set to 'Subject Optional.' Since children learning 
Spanish frequently hear subjectless sentences, whereas those learning
English do not, the parameter setting is switched in the Spanish 
learner, but remains set at the default for the English learner. 
(Roeper and Williams 1987 is the *locus classicus* for 
parameter-setting models; Ayoun 2003 is more up-to-date; Pinker, 
1997: ch.3 provides a helpful, non-technical overview.)




These two approaches to language acquisition clearly differ 
significantly in their conception of the nature of the learning 
process and the learner's role in it, but we are not concerned to 
evaluate their respective merits here. Rather, the important point 
for our purposes is that they both attribute substantial amounts of 
innate information *about language* to the language learner. 
In what follows, we will look in more detail at the various arguments
that have been used to support this 'nativist' theory of 
language acquisition. We will focus on the following question:



> 
> 
> What evidence is there that children come to the language learning task
> equipped with a specialized store of inborn linguistic information,
> such as that specified in the linguist's theory of
> Universal Grammar?




Terminological Note: As Chomsky acknowledges (e.g., 1986:28-29), 
'Universal Grammar' is used with a systematic ambiguity 
in his writings. Sometimes, the term refers to the inborn knowledge 
of language that learners are hypothesized to possess -- the 
content of the 'initial state' of the language faculty 
-- *whatever that knowledge (/content) turns out to be*. 
Other times, 'Universal Grammar' is used to refer to 
certain *specific proposals* as to the content of our innate 
linguistic knowledge, such as the Government-Binding theorist's claim
that we have inborn knowledge of such things as the Principle of 
Structure Dependence, Binding theory, Theta theory, the Empty 
Category Principle, etc.




This ambiguity is important when one is evaluating Chomskyan claims 
that we have innate knowledge of UG. For on the first reading of 
'Universal Grammar' distinguished above, that claim will 
be true so long as *any* form of nativism turns out to be true
of language learners (i.e., so long as they possess *any* 
inborn knowledge about language). On the second reading, however, it 
is possible that learners have innate knowledge of language 
*without* that knowledge's being knowledge of UG (as currently
described by linguists): learners might know things about language, 
yet *not* know Binding Theory, or the Principle of Structure 
Dependence, etc.




In this entry, 'Universal Grammar' will always be used in
the second of these senses, to refer to a specific theory as to the 
content of learners' innate knowledge of language. Where the issue 
concerns merely their having *some or other* innate knowledge 
about language (and is neutral on the question of whether any 
particular theory about that knowledge is true), I will talk of 
'innate linguistic information.' Clearly, an argument to 
the effect that speakers have inborn knowledge of UG entails the 
claim that they have innate linguistic information at their disposal.
The reverse, however, is not the case: there might be reason to think
that a speaker knows something about language innately, without its 
constituting reason to think that what they know is Universal Grammar
as described by Chomksyan linguists; Chomksy might be right that we 
have innate knowledge about language, but wrong about what the 
*content* of that knowledge is. These issues will be 
clarified, as necessary, below.


### 2.2 Chomsky's 'Poverty of the Stimulus' Argument for the Innateness of Language




As we saw in SS1.1, one of the conclusions Chomsky drew from his 
(1959) critique of the Skinnerian program was that language cannot be
learned by mere association of ideas (such as occurs in 
conditioning). Since language mastery involves knowledge of grammar, 
and since grammatical rules are defined over properties of utterances
that are not accessible to experience, language learning must be more
like theory-building in science. Children appear to be 'little 
linguists,' making highly theoretical hypotheses about the 
grammar of their language and testing them against the data provided 
by what others say (and do):



> 
> 
> It seems plain that language acquisition is based on the child's
> discovery of what from a formal point of view is a deep and abstract
> theory -- a generative grammar of his language -- many of
> the concepts and principles of that are only remotely related to
> experience by long and intricate chains of quasi-inferential
> steps. (Chomsky 1965:58)




However, argued Chomsky, just as conditioning was too weak a learning
strategy to account for children's ability to acquire language, so 
too is the kind of inductive inference or hypothesis-testing that 
goes on in science. Successful scientific theory-building requires 
huge amounts of *data,* both to suggest plausible-seeming 
hypotheses and to weed out any false ones. But the data children have
access to during their years of language learning (the 'primary
linguistic data' or '*pld'*) are highly 
impoverished, in two important ways:


1. they constitute a small finite sample of the infinitely many
sentences natural languages contain
2. they do not reliably contain the kinds of sentences that
learners need to falsify incorrect hypotheses




The first type of inadequacy is, of course, endemic to any kind of 
empirical inquiry: it is simply the problem of the underdetermination
of theories by their evidence. Cowie has argued elsewhere that 
underdetermination per se cannot be taken to be evidence for 
nativism: if it were, we would have to be nativists about 
*everything* that people learn (Cowie 1994; 1999). What of the
second kind of impoverishment? If the evidence about language 
available to children does not enable them to reject false 
hypotheses, and if they nonetheless hit on the correct grammar, then 
language learning could not be a kind of scientific inquiry, which 
depends in part on being able to find evidence to weed out incorrect 
theories. And indeed, this is what Chomsky argues: since the 
*pld* are not sufficiently rich or varied to enable a learner 
to arrive at the correct hypothesis about the grammar of the language
she is learning, language could not be learned from the *pld*.




For consider: The fact (i) that the *pld* are finite whereas 
natural languages are infinite shows that children must be 
generalizing beyond the data when they are learning their language's 
grammar: they must be proposing rules that cover as-yet unheard 
utterances. This, however, opens up room for error. In order to 
recover from particular sorts of error, children would need access to
particular kinds of data. If those data don't exist, as (ii) asserts,
then children would not be able to correct their mistakes. Thus, 
since children do eventually converge on the correct grammar for 
their language, they mustn't be making those sorts of errors in the 
first place: something must be stopping them from making 
generalizations that they cannot correct on the basis of the 
*pld*.




Chomsky (e.g., 1965: 30-31) expresses this last point in terms of the
need for *constraints* -- on grammatical concepts, on the
hypothesis space, on the interpretation of data -- and proposes 
that it is innate knowledge of UG that supplies the needed 
limitations. On this view, children learning language are not 
open-minded or naive theory generators -- they are not 
'little scientists.' Instead, the human language-learning
mechanism (the 'language acquisition device' or 
'LAD') embodies built-in knowledge about human languages,
knowledge that prevents learners from entertaining most possible 
grammatical theories. As Chomsky puts it:



> 
> 
> A consideration of...the degenerate quality and
> narrowly limited extent of the available data ...
> leave[s] little hope that much of the structure of the language can be
> learned by an organism initially uninformed as to its general
> character. (1965:58)




Chomsky rarely states the argument from the poverty of the stimulus 
in its general form, as Cowie has done here. Instead, he typically 
presents it *via* an example. One of these concerns learning 
how to form 'polar interrogatives,' i.e., questions 
demanding *yes* or *no* by way of answer, *via* 
a mechanism known as 'auxiliary 
 fronting.'[5]
 Suppose that a child heard pairs of sentences like the following:



> 
> 
> 
> |  |  |
> | --- | --- |
> | 1a. | Jacob is happy today |
> | 1b. | Is Jacob happy today? |
> | 2a. | The girls are dancing |
> | 2b. | Are the girls dancing? |
> 
> 
> 




She wants to figure out the rule you use to turn declaratives like 
(1a) and (2a) into interrogatives like (1b) and (2b). Here are two 
possibilities:



> 
> 
> 
> |  |  |
> | --- | --- |
> | H1. | Find the first occurrence of *is* in the
> sentence and move it to the front. |
> | H2. | Find the first occurrence of *is* following
> the subject nounphrase ('NP') of the sentence, and move it
> to the front. |
> 
> 
> 




Both hypotheses are adequate to account for the data the learner has 
so far encountered. To any unbiased scientist, though, H1 would 
surely appear preferable to H2, for it is *simpler* -- it
is shorter, for one thing, and does not refer to theoretical 
properties, like being a NP, being instead formulated in terms of 
'observable' properties like word order. Nonetheless, H1 
is false, as is evident when you look at examples like (3):



> 
> 
> 
> |  |  |
> | --- | --- |
> | 3a. | [The girl who is in the jumping castle]NP is
> Kayley's daughter |
> | 3b. | \*Is [the girl who in the jumping castle]NP is Kayley's
> daughter? |
> | 3c. | Is [the girl who is in the jumping castle]NP Kayley's
> daughter? |
> 
> 
> 




H1 generates the ungrammatical question (3b), whereas H2 generates 
the correct version, 
 (3c).[6]
 Now, you and I and every other English speaker know (in some sense 
-- see SS3.2.1a) that H1 is false and H2 is correct. 
*That* we know this is evident, Chomsky argues, from the fact 
that we all know that (3b) is not the right way to say (3c). The 
question is how we could have learnt this.




Suppose, for example, that based on her experience of (1) and (2), a 
child were to adopt H1. How would she discover her error? There would
seem to be two ways to do this. First, she could use H1in her own 
speech, utter a sentence like (3b), and be corrected by her parents 
or caregivers; second, she could hear a sentence like (3c) uttered by
a competent speaker, and realize that that sentence is not generated 
by her hypothesis, H1. But typically parents don't correct their 
children's ill formed utterances (see SS2.2.1(c) for more on this), and
worse, according to Chomsky, sentences like (3c) -- sentences 
that are not generated by the incorrect rule H1 and hence would 
falsify it-- do not occur often enough in the *pld* to 
guarantee that every native English speaker will be able to get it 
right.




So in answer to the question: how do we learn that H2 is
better than H1, Chomsky argued that we don't *learn*
this at all! A better explanation of how we all know that
H2 is right and H1 is wrong is that we
were *born knowing* this fact. Or, more accurately, we were
born knowing a certain principle of UG (the 'Principle of
Structure Dependence'), which tells us that rules like
H1 are not worth pursuing, their ostensible
'simplicity' notwithstanding, and that we should always
prefer rules, like H2, which are stated in terms of
sentences' *structural* properties. In sum, we know that
H2 is a better rule than H1, but we didn't learn
this from our experience of the language. Rather, this fact is a
consequence of our inborn knowledge of UG.




Chomskyans contest that there are many other cases in which 
speaker-hearers know grammatical rules, the critical evidence in 
favor of which is missing from the *pld*. Kimball 1973:73-5, 
for instance, argues that complex auxiliary sequences like *might 
have been* are "vanishingly rare" in the 
*pld*, hence that children acquire competence with these 
constructions (in the sense of knowing the order in which to put the 
modal, perfect and progressive elements) without relevant experience.
(Pullum and Scholz 2002, discuss two other well known examples.) 
Nativists thus conclude that numerous other principles of UG are 
innately known as well. Together, these UG principles place strong 
constraints on learners' linguistic theorizing, preventing them from 
making errors for which there are no falsifying data.




So endemic is the impoverishment of the *pld*, according to 
Chomskyans, that it began to seem as if the entire learning paradigm 
were inapplicable to language. As more and more and stricter and 
stricter innate constraints needed to be imposed on the learner's 
hypothesis space to account for their learning rules in the absence 
of relevant data, notions like hypothesis generation and testing 
seemed to have less and less purchase. This situation fuelled the 
recent shift away from hypothesis testing models of language 
acquisition and towards parameter setting models discussed in 
SS2.1 above.


#### 2.2.1 Criticisms of the Poverty of the Stimulus Argument




Many, probably most theorists in modern linguistics and cognitive 
science have accepted Chomsky's poverty of the stimulus argument for 
the innateness of UG. As a result, a commitment to linguistic 
nativism has underpinned most research into language acquisition over
the last 40-odd years. Nonetheless, it is important to understand 
what criticisms have been leveled against the argument, which I 
schematize as follows for convenience:



> 
> 
> 
> The General Form of the Argument from the Poverty of the Stimulus
> 
> 
> 1. Mastery of a language consists (in part) of knowing its
> grammar.
> 2. In order to learn a certain rule of grammar, *G* children would have
> to have access to certain sorts of data, *D*, which falsify competing
> hypotheses.
> 3. The primary linguistic data *(pld)* do not contain *D*.
> 
> 
> 
> 
> So
> 
> 
> 4. *G* could not be learned.
> 5. This situation is quite general: many rules of grammar are
> unlearnable from the *pld*.
> 
> 
> 
> 
> So
> 
> 
> 6. UG is innately known.
> 
> 
> 


##### 2.2.1(a) Premiss 1: Knowledge of grammar




In the 1970's, philosophers contested Chomsky's use of the word 
'know' to describe speakers' relations to grammar, 
arguing that unlike standard cases of propositional knowledge, most 
speakers are utterly unaware of grammatical rules (e.g., 
"Anaphors are bound, and pronominals and R-expressions are free
in their binding domains") and many probably wouldn't 
understand them even if told what they are (Stich 1971). In 
response, Chomsky (e.g., 1980:92) began to use a technical term, 
'cognize,' to describe the speaker-grammar relation, 
avoiding the philosophically loaded term, 'knowledge.'




However, while it is certainly legitimate to propose a special 
relationship between speakers and grammars, unanswered questions 
remain about the precise nature of cognizance. Is it a 
representational relation, like belief? If not, what does 
'learning a grammar' amount to? If so, are speakers' 
representations of grammar 'explicit' or 
'implicit' or 'tacit' -- and what, 
exactly, do any of these terms mean? (See the papers collected in 
MacDonald 1995, for discussion of this last issue; see Devitt 2006 
for arguments that there is no good reason to suppose that speakers 
use any representations of grammatical rules in their production and 
comprehension of language.) Relatedly, how does a speaker's 
cognizance of grammar (her 'competence,' in Chomskyan 
parlance) function in her linguistic 'performance' 
-- i.e., in the actual production or comprehension of an 
utterance?




These issues bear on the argument from the poverty of the stimulus 
because that argument may appear more or less impressive depending on
the answers one gives to them. If, for instance, one held that 
grammars are belief-like entities, explicitly represented in our 
heads in some internal code (cf. Stich 1978), then the question of 
how those beliefs are acquired and justified is indeed a pressing one
-- as, for different reasons, is the question of how they 
function in performance (see Harman 1967, 1969). However, if one 
were to deny that grammar is represented at all in the heads of 
speakers, like Devitt 2006 and Soames 1984, then the issue of how 
language is learned and what role 'evidence' etc. might 
play in that process takes on a very different cast. Or if, to take a
third possibility, one were to reject generative syntax altogether 
and adopt a different conception of what the content of speakers' 
grammatical knowledge is -- along the lines of Tomasello 
(2003), say -- then that again affects how one views the learning 
process. In other words, one's ideas about *what is learned* 
affect one's conception of *what is needed to learn it*. Less 
'demanding' conceptions of the outputs of language 
acquisition require less demanding conceptions of its input (whether 
experiential or inborn); this last approach to the problem of 
language learning is discussed further in SS2.2.1 below.


##### 2.2.1(b) Premiss 2: The learning algorithm




In the example of polar interrogatives, discussed above, we saw how 
children apparently require explicit falsifying evidence in order to 
rule out the plausible-seeming but false hypothesis, H1. Premiss 2 of
the argument generalizes this claim: there are many instances in 
which learners need specific kinds of falsifying data to correct 
their mistakes (data that the argument goes on to assert are 
unavailable). These claims about the data learners would need in 
order to learn grammar are underpinned by certain assumptions about 
the learning algorithm they employ. For example, the idea that false 
hypotheses are rejected only when they are explicitly falsified in 
the data suggests that learners are incapable of taking any kind of 
probabilistic or holistic approach to confirmation and 
disconfirmation. Likewise, the idea that learners unequipped with 
inborn knowledge of UG are very likely indeed to entertain false 
hypotheses suggests that their method of generating hypotheses is 
insensitive to background information or past experience. (e.g., 
information about what sorts of generalizations have worked in other 
contexts




The non-nativist language learner as envisaged by Chomsky in the 
original version of the poverty of the stimulus argument, in other 
words, is limited to a kind of Popperian methodology -- one that
involves the enumeration of all possible grammatical hypotheses, each
of which is tested against the data, and each of is rejected just in 
case it is explicitly falsified. As much work in philosophy of 
science over the last half century has indicated, though, nothing 
much of anything can be learned by this method: the world quite 
generally fails to supply falsifying evidence. Instead, hypothesis 
generation must be inductively based, and (dis)confirmation is a 
holistic matter.




Thus arise two problems for the Chomskyan argument. First, it is not 
all that surprising to discover that if language learners employed a 
method of conjecture and refutation, then language could not be 
learned from the data. In other words, the poverty of the stimulus 
argument doesn't tell us much we didn't know already. Secondly, and 
as a result, the argument is quite weak: it makes the negative point 
that language acquisition does not occur via a Popperian learning 
strategy, but it favors no specific alternative to this acquisition 
theory. In particular, the argument gives no more support to a 
nativist (UG-based) theory than to one that proposed (say) that 
learners formulate grammatical hypotheses based on their extraction 
of statistical information about the *pld* and that they may 
reject them for reasons other than outright falsification -- 
because they lack explicit confirmation, or because they do not 
cohere with other parts of the grammar, for instance.




In reply, some Chomskyans (e.g., Matthews 2001) challenge 
non-nativists to produce these alternative theories and submit them 
to empirical test. It's pointless, they claim, for nativists to try 
to argue against theories that are mere gleams in the empiricist's 
eye, particularly when Chomsky's approach has been so fruitful and 
thus may be supported by a powerful inference to the best 
explanation. Others have argued explicitly against particular 
non-nativist theories -- Marcus 1998, 2001, for instance, 
discusses the shortcomings of connectionist accounts of language 
acquisition.




A recent book by Michael Tomasello (Tomasello 2003) addresses the 
nativist's demand for an alternative theory directly. Tomasello 
argues that language learners acquire knowledge of syntax by using 
inductive, analogical and statistical learning methods, and by 
examining a broader range of data for the purposes of confirmation 
and disconfirmation. He argues that children formulate abstract 
syntactic generalizations rather late in the learning process (around
the age of 4 or 5) and that their earliest utterances are governed by
much less general rules of thumb, or 'constructions.' 
More abstract constructions, framed in increasingly adult-like and 
'syntactic' terms, are progressively formulated through 
the application of pattern-recognition skills ('analogy')
and a kind of statistical analysis of both incoming data and 
previously acquired constructions, which Tomasello calls 
'functional distributional 
 analysis.'[7]





Tomasello's theory differs from a Chomskyan approach in three 
important respects. First, and taking up a point mentioned in the 
previous section, it employs a different conception of linguistic 
competence, the end state of the learning process. Rather than 
thinking of competent speakers as representing the rules of grammar 
in the maximally abstract, simple and elegant format devised by 
generative linguists, Tomasello conceives of them as employing rules 
at a variety of different levels of abstraction, and, importantly, as
employing rules that are not formulated in purely syntactic terms. He
adopts a different type of grammar, called 
'cognitive-functional grammar' or 'usage-based 
grammar,' in which rules are stated partly in terms of 
syntactic categories, but also in semantic terms, that is, in terms 
of their patterns of use and communicative function. A second respect
in which Tomasello's approach differs from that of most theorists in 
the Chomskyan tradition, is in employing a much richer conception of 
the 'primary linguistic data,' or *pld*. For 
generative linguists, the *pld* comprises a set of sentences, 
perhaps subject to some preliminary syntactic analysis, and the child
learning grammar is thought of as embodying a function which maps 
that set of sentences onto the generative grammar for her language. 
On Tomasello's conception, the *pld* includes not just a set 
of sentences, but also facts about how sentences are used by speakers
to fulfill their communicative intentions. On his view, semantic and 
contextual information is also used by children for the purposes of 
acquiring grammatical knowledge.




Tomasello argues that by adopting a more 'user-friendly' 
conception of natural language grammars and by radically expanding 
one's conception of the language-relevant information available to 
children learning language, the 'gap' exploited by the 
argument from the poverty of the stimulus -- that is, the gap 
between what we know about language and the data we learn it from 
-- in large part disappears. This gives rise to a third 
important respect in which Tomasello's theory differs from that of 
the linguistic nativist. On his view, children learn language without
the aid of any inborn linguistic information: what children bring to 
the language learning task -- their innate endowment -- is 
not language-specific. Instead, it consists of 'mind 
reading,' together with perceptual and cognitive skills that 
are employed in other domains as well as language learning. These 
skills include: (i) the ability to share attention with others; (ii) 
the ability to discern others' intentions (including their 
communicative intentions); (iii) the perceptual ability to segment 
the speech stream into identifiable units at different levels of 
abstraction; and (iv) general reasoning skills, such as the ability 
to recognize patterns of various sorts in the world, the ability to 
make analogies between patterns that are similar in certain respects,
and the ability to perform certain sorts of statistical analysis of 
these patterns. Thus, Tomasello's theory contrasts strongly with the 
nativist approach.




Although assessing Tomasello's theory of language acquisition is 
beyond the scope of this entry, this much can be said: the 
oft-repeated charge that empiricists have failed to provide 
comprehensive, testable alternatives to Chomskyanism is no longer 
sustainable, and if the what and how of language acquisition are 
along the lines that Tomasello describes, then the motivation for 
linguistic nativism largely disappears.


##### 2.2.1(c) Premiss 3: What do the *pld* contain?




A third problem with the poverty of the stimulus argument is that 
there has been little systematic attempt to provide empirical 
evidence supporting its assertions about what the *pld* 
contain. This is an old complaint (cf. Sampson 1989) which has 
recently been renewed with some vigor by Pullum and Scholz 2002, 
Scholz and Pullum 2002, and Sampson 2002. Pullum and Scholz provide
evidence that, contrary to what Chomsky asserts in his discussion of 
polar interrogatives, children can expect to encounter plenty of data
that would alert them to the falsity of H1. Sampson 2002, mines the
'British National Corpus/demographic,' a 100 million word
corpus of everyday British speech (available online at 
http://info.ox.ac.uk/bnc/), for evidence that contrary to Kimball's 
contention that complex auxiliaries are 'vanishingly 
rare,' they in fact occur quite frequently (somewhere from once
every 10,000 words to once every 70,000 words, or once every couple 
of days to once a week).




Chomskyans respond in two main ways to findings like this. First, 
they argue, it is not enough to show that *some* children can 
be expected to hear sentences like *Is the girl in the jumping 
castle Kayley's daughter?* *All* children learn the 
correct rule, so the claim must be that *all* children are 
guaranteed to hear sentences of this form -- and this claim is 
still implausible, data like those just discussed 
 notwithstanding.[8]
 In order to take this question further, it would be necessary to 
determine when in fact children master the relevant structures, and 
vanishingly little work has been done on this topic. Sampson 
2002:82ff. found no well-formed auxiliary fronted questions (like 
*Is the girl who is in the jumping castle Kayley's daughter?*)
in his sample of the British National Corpus. He notes that in 
addition to supporting Chomsky's claims about the poverty of the 
*pld*, such data simultaneously problematize his claims about 
children's knowledge of the auxiliary-fronting rule itself. Sampson 
found that speakers invariably made errors when apparently attempting
to produce complex auxiliary-fronted questions, and often emended 
their utterance to a tag form instead (*e.g., The girl who's in 
the jumping castle is Kayley's daughter, isn't she?).* 
Hespeculates that the construction is not idiomatic even in adult 
language, and that speakers learn to form and decode such questions 
much later in life, after encountering them in written English. If 
that were the case, then the lack of complex auxiliary fronted 
questions in the *pld* would be both unsurprising and 
unproblematic: young children don't hear the sentences, but nor do 
they learn the rule. To my knowledge, children's competence with the 
auxiliary fronting rule has not been addressed 
 empirically.[9]





Secondly, Chomskyans may produce other versions of the poverty of the
stimulus argument. For instance, Crain 1991 constructs a poverty of 
the stimulus argument concerning children's acquisition of knowledge 
of certain constraints on movement. However, while Crain's argument 
carefully documents children's conformity to the relevant grammatical
rules, its nativist conclusion still relies on unsubstantiated 
intuitions as to the non-occurrence of relevant forms or evidence in 
the *pld*. It is thus inconclusive. (Cf. Crain 1991; Crain's 
experiments and their implications are discussed in Cowie 
1999 ; Cf. also Crain and Pietrowski 2001, 2002).


##### 2.2.1(d) The validity of the argument




The argument from (1), (2), and (3) to (4) appears valid. However, as
is implicit in my discussion of premiss (2), an equivocation between 
different senses of 'learning' threatens. What (1)-(3) 
show, if true, is that grammar G can't be learned from the 
*pld* by a learner *using a 'Popperian' learning
strategy,* that is, a strategy of 'bold conjecture'
and refutation. What (4) concludes, however, is that G is unlearnable,
period, from the *pld* -- a move that several authors,
particularly connectionists, have objected to. (See especially
Elman *et al*. 1996 and Elman 1998 for criticisms of Chomskyan
nativism along these lines; see Marcus 1998 and 2001 for
responses.)




Chomskyans typically take this point, conceding that the argument 
from the poverty of the stimulus is not apodeictic. Nonetheless, they
claim, it's a very good argument, and the burden of proof belongs 
with their critics. After all, nativists have shown the falsity of 
the only non-nativist acquisition theories that are well-enough 
worked out to be empirically testable, namely, Skinnerian behaviorism
and Popperian conjecture and refutation. In addition, they have 
proposed an alternative theory, Chomskyan nativism, which is more 
than adequate to account for the phenomena. In empirical science, 
this is all that they can reasonably be required to do. The fact that
there might be other *possible* acquisition algorithms which 
*might* account for children's ability to learn language is 
neither here nor there; nativists are not required to argue against 
mere possibilities.




In response, some non-nativists have argued that UG-based theories 
are not in fact good theories of language acquisition. Tomasello 
(2003: 182ff.), for instance, identifies two major areas of 
difficulty for UG-based theories, such as the 
principles-and-parameters approach. First, there is the 
'linking' problem, deriving from the fact of linguistic 
diversity: almost no UG-based accounts explain how children link the 
highly abstract categories of UG to their instantiations in the 
particular language they happen to be 
 learning.[10]
 His example is the category 'Head,' In order to set the 
'Head parameter,' a child needs to be able to identify 
which words in the stream of noise she is hearing are in fact clausal
heads. But heads "do not come with identifying tags on them in 
particular languages; they share no perceptual features in common 
across languages, and so their means of identification cannot be 
specified in [UG]" (Tomasello 2003:183). Second, there is the 
problem of developmental change, also emphasized by Sokolov and Snow,
1991. It is difficult to see how UG-based approaches can account for 
the fact that children's linguistic performance seems to emerge 
piecemeal over time, rather than emerging in adult-like form all at 
once, as the parameter-setting model suggests it 
 should.[11]
 In response, generativists have appealed to such notions as 
'maturational factors' or 'performance 
factors.' But, Tomasello argues, such measures are ad hoc in 
the absence of a detailed specification of what these maturational or
performance factors are, and how they give rise to children's actual 
performance.




At the very least, such objections serve to equalize the burden of 
proof: non-nativists certainly have work to do, but so too do 
nativists. Merely positing an innate UG and a 
'triggering' mechanism by which it 'grows' 
into full-fledged language is insufficient. Nativists need to show 
how their theory can account for the known course of language 
acquisition. Merely pointing out that there is a *possibility*
that such theories are true, and that they would, if true, explain 
how language learning occurs in the face of an allegedly impoverished
stimulus, is only part of the job.


##### 2.2.1(e) Premiss 5: How general is the poverty of the stimulus?




Because they are defending the view that all of UG is inborn, 
Chomskyans must be credited with holding that the primary data are 
impoverished quite generally. That is, if the innateness of UG 
*tout court* is to be supported by poverty of the stimulus 
considerations, the idea must be that the cases that nativists 
discuss in detail (polar interrogatives, complex auxiliaries, etc.) 
are but the tip of the unlearnable iceberg. Nativists quite 
reasonably do not attempt to defend this claim by endless enumeration
of cases. Rather, they turn to another kind of argument to support 
the 'global impoverishment' position. This argument is 
sometimes called the 'Logical Problem of Language 
Acquisition'; here, we will call it 'The Unlearning 
Problem.' It will be discussed in section 3.


##### 2.2.1(f) The validity of the argument (II): What is inborn?




Suppose that the primary linguistic data were impoverished in all the
ways that nativists claim and suppose, too, that children know a 
bunch of things for which there is no evidence available -- 
suppose, as Hornstein and Lightfoot (1981:9) put it, that 
"[p]eople attain knowledge of the structure of their language 
for which *no* evidence is available in the data to which they
are exposed as children." What follows from this is that there 
must be constraints on the learning mechanism: children do not 
enumerate all possible grammatical hypotheses and test them against 
the data. Some possible hypotheses must be ruled out *a 
priori*. But, critics allege, what does *not* follow from 
this is *any particular view about the nature of the requisite 
constraints*. (Cowie 1999: ch.8.) A fortiori, what does not 
follow from this is the view that Universal Grammar (construed as a 
theory about the structural properties common to all natural 
languages, per Terminological Note 2 above) is inborn.




For all the poverty of the stimulus argument shows, the constraints 
in question might indeed be language-specific and innate, but with 
contents quite different from those proposed in current theories of 
UG. Or, the constraints might be innate, but not language-specific. 
For instance, as Tomasello 2003 argues, children's early linguistic 
theorizing appears to be constrained by their inborn abilities to 
share attention with others and to discern others' communicative 
intentions. On his view, a child's early linguistic hypotheses are 
based on the assumption that the person talking to him is attempting 
to convey information about the thing(s) that they are both currently
attending to. (Another example of an innate but non-language specific
constraint on language learning derives from the structure of the 
mammalian auditory system; 'categorical perception,' and 
is relation to the acquisition of phonological knowledge is discussed
below, SS3.3.4.). Another alternative is that the constraints 
might be learned, that is, derived from past experiences. An example 
again comes from Tomasello (2003). He argues that 
*entrenchment*, or the frequency with which a linguistic 
element has been used with a certain communicative function, is an 
important constraint on the development of children's later syntactic
knowledge. For instance, it has been shown experimentally that the 
more often a child hears an element used for a particular 
communicative purpose, the less likely she is to extend that element 
to new contexts. (See Tomasello 2003:179).




In short, there are many ways to constrain learners' hypotheses about
how their language works. Since the poverty of the stimulus argument 
merely indicates the need for constraints, it does not speak to the 
question of what sorts of constraints those might be.




In response to this kind of point, Chomskyans point out that the 
innateness of UG is an empirical hypothesis supported by a perfectly 
respectable inference to the best explanation. Of course there is a 
*logical* space between the conclusion that something 
constrains the acquisition mechanism and the Chomskyan view that 
these constraints are inborn representations of Binding Theory, Theta
theory, the ECP, the principle of Greed or Shortest Path and so on. 
But the mere fact that the argument from the poverty of the stimulus 
doesn't *prove* that UG is innately known is hardly reason to 
complain. This is science, after all, and demonstrative proofs are 
neither possible nor required. What the argument from the poverty of 
the stimulus provides is good reason to think that there are strong 
constraints on the learning mechanism. UG is at hand to supply a 
theory of those constraints. Moreover, that theory has been highly 
productive of research in numerous areas (linguistics, 
psycholinguistics, developmental psychology, second language 
research, speech pathology etc. etc.) over the last 50 years. These 
successes far outstrip anything that non-nativist learning theorists 
have able to achieve even in their wildest dreams, and support a 
powerful inference to the best explanation in the Chomskyan's favor.


##### 2.2.1(g) Who has the burden of proof?




As seen above (SS2.2.1(d)), however, the strength of the 
Chomskyan's ability to explain the phenomena of language acquisition 
has been questioned, and with it, implicitly, the strength of her 
inference to the best explanation. In addition, there is a general 
debate within the philosophy of science as to the soundness of 
inferences to the best explanation: does an explanation's being the 
best available give any additional reason (over and above its ability
to account for the phenomena within its domain) to suppose it true? 
[Link to Encyclopedia Article 'Abduction' by Peter 
Achinstein for more on this topic.]




In the linguistic case, what sometimes seems to underpin people's 
positions on such issues is differing intuitions as to who has the 
burden of proof in this debate. Empiricists or non-nativists contend 
that Chomskyans have not presented enough data (or considered enough 
alternative hypotheses) to establish their case. Chomskyans reply 
that they have done more than enough, and that the onus is on their 
critics either to produce data disconfirming their view or to produce
a testable alternative to it.




That such burden-shifting is endemic to discussions of linguistic 
nativism (the exchange in Ritter 2002 is illustrative) suggests to 
me that neither side in this debate has as yet fulfilled its 
obligations. Empiricists about language acquisition have ably 
identified a number of points of weakness in the Chomskyan case, but 
have only just begun to take on the demanding task of developing 
develop non-nativist learning theories, whether for language or 
anything much else. Nativists have rested content with hypotheses 
about language acquisition and innate knowledge that are based on 
plausible-seeming but largely unsubstantiated claims about what the 
*pld* contain, and about what children do and do not know and 
say.




It is unclear how to settle such arguments. While some may disagree
(especially some Chomskyans), it seems that much work still needs to
be done to understand how children learn language -- and not just
in the sense of working out the details of which parameters get set
when, but in the sense of reconceiving both what linguistic competence
consists in, and how it is acquired. In psychology, a new,
non-nativist paradigm for thinking about language and learning has
begun to emerge over the last 10 or so years, thanks to the work of
researchers like Elizabeth Bates, Jeffrey Elman, Patricia Kuhl,
Michael Tomasello and others. The reader is referred to Elman *et
al*. 1996, Tomasello 2003 and SS3 below for an entree
into this way of thinking.




For now, considerations of space demand a return to our topic, viz., 
linguistic nativism, rather than further discussion of alternatives 
to it.


### 2.3 The Argument from the 'Unlearning Problem'




We saw in the previous section that in order to support the view that
all of UG is innately known, nativists about language need to hold 
not just that the data for language learning is impoverished in a few
isolated instances, but that it's impoverished across the board. That
is, in order to support the view that the innate contribution to 
language acquisition is something as rich and detailed as knowledge 
of Universal Grammar, nativists must hold that the inputs to language
acquisition are defective in many and widespread cases. (After all, 
if the inputs were degenerate only in a few isolated instances, such 
as those discussed above, the learning problem could be solved simply
by positing innate knowledge of a few relevant linguistic hints, 
rather than all of UG.)




Pullum and Scholz (2002:13) helpfully survey a number of ways in 
which nativists have made this point, including:


1. Finiteness: the *pld* (primary linguistic data) are finite,
whereas languages contain infinitely many sentences.
2. Underdetermination: the *pld* are always compatible with
infinitely many grammatical hypotheses.
3. Degeneracy: the *pld* contain ungrammatical and incomplete
sentences.
4. Idiosyncrasy: different children learning the same language are
exposed to different samples of sentences.
5. Positivity: the *pld* contain only positive instances (what
*is* a sentence of the language to be learned, a.k.a. the
'target language').
6. No Feedback: children are not told or rewarded when they get
things right, and are not corrected when they make mistakes.




In this section, I will set aside features (i) and (ii) as being 
characteristic of *any* empirical domain: the data are 
*always* finite, and they *always* underdetermine one's
theory. No doubt it's an important problem for epistemologists and 
philosophers of science to explain how general theories can 
nonetheless be confirmed and believed. No doubt, too, it's an 
important problem for psychologists to explain the mechanisms by 
which individuals acquire general knowledge about the world on the 
basis of their experience. But underdetermination and the finiteness 
of the data are everyone's problem: if these features of the language
learning situation per se supported nativism, then we should accept 
that all learning, in every domain, requires inborn domain-specific 
knowledge. But while it's not impossible that everything we know that
goes beyond the data is a result of our having domain-specific innate
knowledge, this view is so implausible as to warrant no further 
discussion here.




I also set aside features (iii) and (iv). For one thing, it is 
unclear exactly how degenerate the *pld* are; according to one
early estimate, an impressive 99.7% of utterances of mothers to their
children are grammatically impeccable (Newport, Gleitman and 
Gleitman 1977). And even if the data are messier than this figure 
suggests, it is not unreasonable to suppose that the vast weight of 
grammatically well-formed utterances would easily swamp any residual 
noise. As to the idiosyncrasy of different children's data sets, this
is not so much a matter of stimulus poverty as stimulus difference. 
As such, idiosyncrasy becomes a problem for a non-nativist only on 
the assumption that different children's states of linguistic 
knowledge differ from one another less than one would expect given 
the differences in their experiences. As far as I know, no serious 
case for this last claim has ever been 
 made.[12]





In this section, we will focus on features (v) and (vi) of the 
*pld*. For it is consideration of the positivity of the data 
set, and the lack of feedback available to children, that has given 
rise to what I am calling the 'Unlearning Problem,' 
otherwise known (somewhat misleadingly) as the 'Logical Problem
of Language Acquisition.' (For statements of the argument, see,
e.g., Baker 1979; Lasnik; 1989:89-90; Pinker 1989.)



> 
> ![Diagram of possible relationships between H and L](fig2.png)
> Figure 2. Five possible relations between the language generated
> by hypothesis (H) and the target grammar (L)
> 
> 
> 




Take a child learning the grammar of her language, *L*. 
Figure 2 represents the 5 possible relations that 
might obtain between the language generated by her current 
hypothesis, *H*, and that generated by the target grammar, 
*L*. (v) represents the end point of the learning process: the
learner has figured out the correct grammar for her language. A 
learner in situation (i), (ii) or (iii) is in good shape, for she can
easily use the *pld* as a basis for correcting her hypothesis 
as follows: whenever she encounters a sentence in the data (i.e., a 
sentence of *L*) that is not generated by *H*, she has 
to 'expand' her hypothesis so that it generates that 
sentence. In this way, H will keep moving, as desired, towards 
*L*. However, suppose that the learner finds herself in 
situation (iv), where her hypothesis generates all of the target 
language, *L*, and more besides. (Children frequently find 
themselves in this position, for example, they invariably go through 
a phase in which they overgeneralize regular past tense verb endings 
to irregular verbs; their grammars generate the incorrect *\*I 
breaked it* as well as the correct *I broke it*.) There, 
she is in deep trouble, for she cannot use the *pld* to 
discover her error. Every sentence of *L*, after all, is 
already a sentence of *H*. In order to 'shrink' 
her hypothesis -- to 'unlearn' the rules that 
generate *\*I breaked it* -- she needs to know which 
sentences of *H* are not sentences of *L* -- she 
needs to figure out that *\*I breaked it* is not a sentence of 
English. But -- and this is the problem -- this kind of 
evidence, often called 'negative evidence,' is held to be
unavailable to language learners.




For as we have seen, the *pld* is mostly just a sample of 
sentences, of positive instances of the target language. It contains 
little, if any, information about strings of words that are not 
sentences. For instance, children aren't given lists of ungrammatical
strings. Nor are they typically corrected when they make mistakes. 
And nor can they simply assume that strings that haven't made their 
way into the sample are ungrammatical: there are infinitely many 
sentences that are absent from the data for the simple reason that 
no-one's had occasion to say them yet.




In sum: a child who is in situation (iv) -- a child whose 
grammar 'overgenerates' -- would need negative 
evidence in order to recover from her error. Negative evidence, 
however, does not appear to exist. Since children do manage to learn 
languages, they must never get themselves into situation (iv): they 
must never need to 'unlearn' any grammatical rules. There
are two ways they could do this. One would be never to generalize 
beyond the data at all. But clearly, children do generalize, else 
they'd never succeed in learning a language. The other would be if 
there were something that ensured that *when* they generalize 
beyond the data, they don't *overgeneralize*, something, that 
is, that ensures that children don't make errors that they could only
correct on the basis of negative evidence. According to the 
linguistic nativist, this something is innate knowledge of UG.


#### 2.3.1 Criticisms of the 'Unlearning' Argument


##### 2.3.1 (a) What is lacking? Negative data vs. Negative Evidence




First, let's make a distinction between:



> 
> *Negative Data*: explicit information that a given string of
> words is not a sentence of the target language. (E.g., "No,
> that's not how you say it," or "It's *I broke it*
> not *I breaked it,*" or "That string of words is
> ungrammatical," etc.)




and



> 
> *Negative Evidence*: information that would enable a learner to
> tell that a given hypothesis is (very likely to be) incorrect. (See
> below for examples.)




Second, let's abandon the idea, which reappears in many presentations
of the Argument from the Unlearning Problem; that learners' 
hypotheses must be explicitly falsified in the data in order to be 
rejected. Let's suppose instead that learners proceed more like 
actual scientists do -- provisionally abandoning theories due to
lack of confirmation, making theoretical inferences to link data with
theories, employing statistical information, and making defeasible, 
probabilistic (rather than decisive, all-or-nothing) judgments as to 
the truth or falsity of their 
 theories.[13]





Intuitively, viewing the learner as employing more stochastic and 
probabilistic inductive techniques enables one to see how the 
unlearning problem might have been overblown. What the argument 
claims, rightly, is that *negative data* near enough do not 
exist in the *pld*. However, what learners need in order to 
recover from overgeneralizations, is not negative data *per 
se*, but *negative evidence*, and arguably, the 
*pld* do contain significant amounts of that. For example:


1. *Failures of understanding or communication*: others'
failures to understand children's linguistic productions (evidenced
either by requests for repetition or by communicative failure) are
evidence to the learner that there is something wrong with the rule(s)
she was using to generate her utterance. This evidence is not decisive
(maybe Granny just couldn't hear her properly), but it is negative
evidence nonetheless.
2. *Non-occurrence of structural types as negative evidence*: 
Suppose that a child's grammar predicted that a certain string is 
part of the target language. Suppose further that that string never 
appears in the data, even when the context seems appropriate. 
Proponents of the unlearning problem say that non-occurrence cannot 
constitute negative evidence -- maybe Dad simply always chooses 
to say *The girl who is in the jumping castle is Kayley's 
daughter, isn't she?* rather than the auxiliary-fronted version, 
*Is the girl who is in the jumping castle Kayley's daughter?* 
If so, it would be a mistake for the child to conclude on the basis 
of this information that the latter string is ungrammatical.




But suppose that the child is predicting not strings of words, 
*simpliciter*, but rather strings of words *under a certain
syntactic description* (or, perhaps more plausibly, 
quasi-syntactic description -- the categories employed need not 
be the same as those employed in adult 
 grammars).[14]
 This would enable her to make much better use of non-occurrence as 
negative evidence. For non-occurring strings will divide into two 
broad kinds: those whose structures *have* been encountered 
before in the data, and those whose structures have *not* been
heard before. In the former case, the child has positive evidence 
that strings of that kind are grammatical, evidence that would enable
her to suppose that the non-occurrence of that particular string was 
just an accident. (E.g., she could reason that since she's heard 
*Is that mess that is on the floor in there yours?* many 
times, and since that string has the same basic structure as *Is 
that girl that's in the jumping castle Kayley's daughter?*, the 
latter string is probably OK even though Dad chose not to say it.)




In the case in which the relevant form has *never* been 
encountered before in the data, however, the child is better off: the
fact that she has never heard any utterance with the structure of 
\**Is that girl who in the jumping castle is Kayley's daughter*
or *\*Is that mess that that on the floor in there is yours?* 
is evidence that strings of that type are not sentences. Again, the 
evidence is not decisive, and the child should be prepared to revise 
her grammar should strings of that kind start appearing. Nonetheless,
the non-occurrence of a string, suitably interpreted in the light of 
other linguistic information, can constitute negative evidence and 
provide learners with reason to reject overgeneral grammars.
3. *Positive Evidence as Negative Evidence*. Relatedly, learners 
can also exploit positive evidence as to which strings occur in the 
*pld* as a source of negative evidence -- again in a 
tentative and revisable 
 way.[15]
 Suppose that the child's grammar generated two strings as appropriate
in a given kind of context, but that only one sort of string was ever
produced by those around her. The fact that only strings of the first
kind occur is in this case negative evidence -- defeasible, to 
be sure, but negative evidence nonetheless.




In fact, the use of positive evidence to disconfirm hypotheses is 
endemic to science. For instance, Millikan used positive evidence to 
disconfirm the theory that electrical charge is a quantity that 
varies continuously. In his famous 'Oil Drop' experiment,
he found that the amount of charge possessed by a charged oil drop 
was always a whole-number multiple of --(1.6 x 10-19)C. The 
finding that all observed charges were 'quantized' in 
this manner disconfirmed the competing 'continuous 
charges' hypothesis in the same way that positive evidence can 
disconfirm grammatical 
 hypotheses.[16]
4. *Feedback* The Argument from the 'Unlearning
Problem' also points to the lack of feedback provided to
children learning language. In a famous study often cited by
proponents of the argument, Brown and Hanlon 1970 (see also Brown,
1973 and Brown, Cazden, and Bellugi 1969) found no overt disapproval
by mothers of the syntactic errors of their children, and moreover
found that caregivers had no trouble understanding their charges'
ill-formed utterances. Only semantic errors were occasionally
corrected; grammatical mistakes went unremarked.




However, more recent findings have uncovered evidence indicating that
failures of understanding occur with some regularity, and that there 
is a wealth of feedback about correct usage in the language-learning 
environment. For example:


* Hirsh-Pasek, Trieman and Schneiderman (1984) studied interactions
between 2 year olds and their parents, and discovered that caregivers
repeated and corrected 20.8% of flawed sentences, whereas they only
repeated (without correction) 12.0% of well-formed utterances.
* Demetras, Post and Snow (1986) found that in general, only
well-formed sentences were repeated verbatim by parents, and that
ill-formed sentences were not repeated verbatim, but were rather
followed by clarification questions ("What?" --
indicating a lack of understanding) or expansions and/or recasts,
correcting the error.
* Bohannon and Stanowicz (1988) found that 34% of syntactic and 35%
of phonological errors received some form of differential feedback
(e.g., repetitions with corrections or explicit rejection of the
utterance); that more than 90% of parents' exact repetitions
follow well-formed sentences; and that more than 70% of recasts and
expansions follow ill-formed utterances.
* Chouinard and Clark's (2003) longitudinal study of five
children learning language found that parents reformulate erroneous
utterances more often than correct utterances, that they respond
equally often to all error types (phonological, lexical, syntactic,
semantic), and that they correct younger children, who make more
errors, more frequently.
* Perhaps most tellingly, Moerk (1991) performed a reanalysis of
Brown's "Eve" transcripts (among those on which the
1970 'no feedback claim was based) and found many instances in
which Eve's semantic and syntactic errors were explicitly
corrected, including: her use of noun labels; VPs (tense, modality,
auxiliaries); determiners and prepositions; word order (these last
sorts of error were rare, but were invariably corrected).
* Bohannon, MacWhinney and Snow (1990) review other results in this
vein, as well as responding to nativist criticisms of these findings
and their bearing on the unlearning problem.


##### 2.3.1 (b) Children Can and Do Learn from 'Noisy' Data and Exploit Statistical Regularities




Chomsky has recognized the existence of such 'indirect' 
negative data in the *pld*. However, he concluded that they 
were too few and ambiguous to be of aid to the language learner. The 
sorts of findings reported above seem to show that negative evidence 
is pervasive in the *pld.* But can children learn from these 
sorts of statistical regularities?




Standard 
 formulations[17]
 of the 'Unlearning Problem', assume that they cannot: the
view seems to be that learning can only take place under idealized 
conditions where the world supplies unambiguous evidence pro or con 
the language learner's grammatical theories. Given such a conception 
of the learner, none of the examples of feedback just discussed will 
seem relevant to the problem. For only a learner employing fairly 
sophisticated data-analysis techniques and a confirmation measure 
that is sensitive to small changes in probabilities would be able to 
exploit the sorts of regularities in the linguistic environment that 
we have just discussed. However, there is increasing evidence that 
children are in fact remarkably sensitive to subtle feedback, in both
linguistic and non-linguistic domains. For instance:


* Bohannon and Stanowicz (1988) found that children pay particular
attention to parental corrections of their mistakes: they imitate
25.6% of adult expansions (saying the same thing as the child, but
giving more detail) and recasts (repetitions of the child's
utterance, correcting errors), whereas they only imitate 3.6% of exact
or verbatim repetitions by parents of the child's utterance.
* Relatedly, Farrer (1990 1992) found that children were more
likely to repeat a given morpheme if it were part of an adult recast
of one of the child's own sentences, than if it were part of a a
non-repetitious adult utterance (e.g., a change of subject or a
continuation of the conversation). She also found that
children's repetition of adult utterances facilitated the
child's acquisition of various grammatical morphemes.
* Morgan and Travis (1989) and Morgan *et al*. (1995)
dispute the long-term efficacy of such corrective feedback; Bohannonn
*et al*. 1996 respond.
* However, in both longitudinal studies of children in natural
environments (Chouinard and Clark 2003) and in experimental studies
(Saxton *et al*. 1998, and Saxton 1997, Saxton, Backley and Galloway,
2003) the long-term efficacy of feedback has been demonstrated.




In addition, it is becoming increasingly clear that babies, children,
adults and many other mammals are highly sensitive not just to 
feedback, but to other non-obvious statistical regularities in their 
experience. For example:


* Saffran, Aslin and Newport (1996) found that 8 month old babies
were able to learn where the word boundaries in an artificial language
occurred after a mere 2 minutes' exposure to a stream of
artificial speech. The stream consisted of 3-syllable nonsense words
(*bidaku*, *padoti*, *golabu*) repeated
continuously for 2 minutes (*bidakupadotigolabubidakugolabi
...*etc.). The stream was constructed so that the
'transitional probability' of two sounds X#Y was equal to
1 when the sounds formed part of a word, and equal to 1/3 when the
sounds spanned a word boundary. In two minutes, the infants had
learned to discriminate the 'words' (like *bidaku)*
from the 'non-words' (e.g., *kupado*). See also
Chambers, Onishi and Fisher 2003.
* Other studies have expanded upon these results, indicating that
children and babies are sensitive to patterns in a wide range of
verbal cues, such as linguistic rhythm (Nazzi and Ramus 2003);
prosodic stress (Thiessen and Saffran 2003) and voicing and syllabic
structure (Saffran and Thiessen 2003).
* Moreover, there is increasingly persuasive evidence that
statistical or 'distributional' information may be used
not just for the extraction of word boundaries, but -- contrary
to an old argument of Chomsky's -- to limn higher levels of
syntactic structure as well -- see, e.g., Redington and Chater,
1998; Pena *et al*. 2002; Mintz 2002; Saffran 2002; Saffran and
Wilson 2003; Newport and Aslin 2004. Chater and Manning 2006 provide
a survey.)
* Finally, and forestalling any response along the lines that what
we are seeing here is just the nativist's 'Language Acquisition
Device' in action, a number of studies have shown that similar
mechanisms appear to be at work in learning in non-linguistic domains
(Saffran 2002, studied learning of non-linguistic sounds and shapes);
in adults (Pena *et al*. 2002); and in other animals, such as
cotton-top tamarin monkeys (Hauser 2001; Hauser, Weiss and Marcus,
2002).




Taken together, these kinds of results raise the possibility that 
some of the foundational learning mechanisms involved in language 
acquisition are not language specific. If it turns out that babies 
employ the sorts of distributional analysis studied by Saffran, 
Redington and Chater, Pena, and Mintz not only in learning artificial
languages, but also in learning natural languages, then that is 
evidence against linguistic nativism. For this type of learning is 
employed by humans and other animals in other contexts as well: 
whatever is involved in language learning -- be it innate or not
-- is not language-specific.


##### 2.3.1 (c) The Generality of the Argument




The previous objections to the Unlearning Problem Argument made the 
points, first, that negative evidence does exist in the *pld* 
(in the form of regularities both in others' language use and in how 
others react to children's own productions), and second, that 
children (and other animals) seem very good at exploiting this kind 
of information for the purposes of learning about their world. This 
would seem to be rather a good thing, given that there is reason to 
think that learners *must* be able to learn in domains where 
explicit negative data do not exist, and in the absence of 
specialized innate knowledge of those domains. For the unlearning 
problem is a problem for learning from experience quite generally. 
That is, there are many domains in which learners lack explicit 
evidence as to what things are *not*: trees are not cars, 
Irish stews are not curries, birds are not fish and MacDonald's is 
not a branch of the CIA. No-one ever told you any of these things, 
but it's crazy to think that you now know them because you possess 
analogs to the 'Language Acquisition Device' for each of 
these domains. Clearly, in at least some areas, people are able to 
learn an awful lot on the basis of largely positive data, and while 
this of course does nothing to show that language is one of those 
areas, it does indicate that the Unlearning problem argument by 
itself is no argument for linguistic nativism at all, let alone for 
the Chomskyan (UG-based) version of that position.


## 3. Other Research Bearing on the Innateness of Language: New Problems for the Nativist?




In this section, I will mention some other avenues of research that 
have been argued to have a bearing on the innateness of language. My 
goal is not to give an exhaustive survey of these matters, but rather
to provide the interested reader with a way into the relevant 
literatures. Still, I will try to give enough details so as to make a
case that current empirical findings, together with the flaws 
identified in SSSS1 and 2 in the positive arguments for 
linguistic nativism, tend to militate against that position.


### 3.1 Linguistic Universals




Chomsky and others (e.g., Chomsky 1988:46-7; Pinker 1994:237-8) 
have pointed to the existence of 'linguistic universals' 
as supporting the idea that language is the product of a distinct 
faculty of mind. Universals are features thought to be common to all 
natural languages, such as the existence of constraints on the 
movement of elements during a derivation or, less controversially, 
the existence of a syntactic distinction between nouns and verbs. But
not only is the existence of true universals a contested matter (see 
e.g., Maratsos 1989:111), it is unclear what the correct explanation
of them -- assuming they exist -- is would be.




One explanation is certainly the Chomskyan one that they are 
consequences of speakers' innate knowledge of UG. Another is that 
they derive from other, non-linguistically-specific features of 
cognition, such as memory or processing constraints (e.g., Berwick 
and Weinberg 1983 trace certain constraints on movement to 
limitations on parsing imposed by the structure of human memory). Yet
another is that they derive from universal demands of the 
communication situation (e.g., Sapir 1921, argued that the 
distinction between nouns and verbs arises from the fact that 
language is used to communicate propositions, hence needs a way to 
bring an object subject to mind and a way to say something about it).
Finally, as Putnam 1971 speculated, universals might be relics of an
ancestral Ur-language from which all other languages evolved. This 
last hypothesis has generally been rejected as lacking in empirical 
support. However, recent findings in genetics and historical 
linguistics are converging to suggest that all human populations 
evolved from a small group migrating from Africa in the fairly recent
past, and that all human languages have probably evolved from the 
language spoken by that group. (Cavalli-Sforza 1997.)




The Ur-language hypothesis is not, of course, inconsistent with 
linguistic nativism. However, if true, it does weaken any 
*argument* from the existence of universals to the innateness 
of linguistic knowledge. For if languages have a common ancestor, 
then it is possible to explain universals -- even ones that seem
strange from a functional point of view -- as being the result 
of our ancestors' having adopted a certain solution to a linguistic 
coordination problem. Like driving on the right side of the road, a 
solution once established may become entrenched, because the benefits
of everyone's conforming to the same rule outweigh the costs of 
changing to a different rule, and this may be so even if the new rule
were in some sense more 'reasonable.' Thus, even 
arbitrary or odd features of language can be explained historically, 
without positing either compelling functional considerations or 
inborn linguistic 
 constraints.[18]





If, by contrast, language emerged independently in a number of areas,
the existence of universals would be a strong argument for nativism, 
For in that case, it would be implausible to maintain that each 
ancestral group 'just happened' to select the same 
solutions to the various coordination problems they encountered. More
plausible would be the supposition that the different groups' choice 
of the rule was driven by something *internal to speakers*, 
such as, perhaps, an innate representation of UG. In short: if 
languages have a common ancestor, then common descent from originally
arbitrary linguistic conventions is a possible explanation of 
linguistic universals, including the 'odd' or 
'arbitrary' ones that don't seem to have any real 
functional significance. If they don't, then such universals 
seemingly could only be explained in terms of features internal to 
speakers.


### 3.2 Language Localization



> 
> ![Broca's and Wernicke's area diagram](broca-wernicke.png)
> 
> 
> Figure 3. Broca's area and Wernicke's area
> 
> 
> 




Beginning with the work of Broca and Wernicke in the 19th century, a 
popular view has been that language is localized to certain areas of 
the brain (see Fig. 3), almost always the left 
 hemisphere,[19]
 and that it is subject to characteristic patterns of breakdown, 
called 'aphasias.' (See Saffran 2000 for a survey of the
various aphasias.) For example, Broca's area is strongly implicated 
in speech production, and damage to this area can result in a 
characteristic inability ('Broca's aphasia' or 
'agrammatism') to produce fluent speech, especially 
complex grammatical structures and grammatical morphemes. The fact 
that syntax can apparently be selectively interfered with by lesions 
to Broca's area has been taken by some to indicate that grammatical 
knowledge is localized to that area, and this in turn has been taken 
to show support the view that there is a special biological inborn 
basis for that knowledge. (Lenneberg 1964, 1967 is the original 
proponent of this argument, which is echoed in more recent 
discussions, such as Pinker 1994:297-314.)




It is unclear, however, why this inference should seem compelling.
First, as Elman *et al*. 1996 argue, neural localization of
function can occur as a result of virtually any developmental
trajectory: the localization of some function bears not at all on its
innateness.




Secondly, it is now known that neural localization for language is 
very much a relative, rather than an all-or-nothing matter (Dronkers 
*et al*. 2000, Dick *et al*. 2001, Martin 2003). Not
only is language processing widely distributed over the brain (see
Fig. 4), but traditionally language-specific areas of cortex are
implicated in a variety of non-linguistic tasks as well. Broca's area,
for instance, 'lights up' on MEG scans
(magnetoencephalography, a method for measuring changes in the
magnetic properties of the brain due to electrical activity) when
subjects hear a discordant musical sequence in much the same way as it
does when they hear an ungrammatical utterance. (Maess *et
al*. 2001; a special issue of *Nature Neuroscience*, 6(7),
July 2003, explores the implications of this finding.)




Finally, recent studies of cortical plasticity have shown that even
the most plausible candidates for innate specification -- such as
the use of visual cortex for vision or the use of auditory cortex for
hearing -- exhibit high degrees of experience-dependent
plasticity. For example, in congenitally blind subjects, the areas of
the brain normally used for seeing are taken over for the processing
of Braille (Sadato *et al*. 1996; Hamilton and Pascual-Leone,
1998) and even in those with late-onset blindness, significant
'rewiring' of visual cortex for other perceptual tasks is
apparent (Kujala *et al*. 1997). Likewise, in the congenitally deaf,
auditory cortex is used for the processing of sign language (Nishimura
*et al*. 1999, von Melchner, Pallas and Sur 2000). (See Shimojo and
Shams 2001, for a review.)



> 
> ![pet scan images](PosnerRaichle.jpg)
> 
> 
> Figure 4. Pet scan showing brain regions involved in various language
> tasks. From Posner and Raichle (1997, 15). Used by permission of M. 
> Raichle.
> 
> 
> 




As Marcus (2004:40-45) points out in response to Elman *et
al*. 1996, the ability of the brain to 'rewire' itself
under exceptional circumstances is consistent with its having been
'prewired,' or set up, differently by the genes. However,
these sorts of data indicate that complex functions, such as are
involved in processing sign language, can be carried out in areas of
brain that are 'prewired' (if they are) to do something
quite different. This suggests that these abilities require little in
the way of task-specific pre-wiring, and are learned largely on the
basis of experience (together with whatever sort of 'prewiring' is
supplied for the cortex as a whole). That is, if sign language
processing tasks can be carried out by areas of cortex that are
presumably innately predisposed (if they are) to do auditory
processing, then the former competence must be being learned in the
absence of inborn constraints or knowledge that are specific to that
task. Of course, these are pathological cases, and it is unclear
whether the subjects in these experiments had any special training in
order that their brains were 'rewired' in these
ways. Nonetheless, examples like these provide an existence proof of
the brain's ability to acquire complex processing capacities --
indeed, processing capacities relevant to language -- in the
complete absence of inborn, domain-specific information. As such, they
raise the possibility that other aspects of language processing are
similarly acquired in the absence of task-specific constraints.




In sum, the neuroscientific evidence currently available provides no 
support for linguistic nativism. The suggestion that localization of 
function is indicative of a substantial degree of innate 
prespecification is no longer tenable: localization can arise in many
different ways. In addition, linguistic functions do not seem to be 
particularly localized: language use and understanding are complex 
tasks, involving many different brain areas -- areas that are in
at least some cases implicated also in other tasks. It is hard to see
how to reconcile these facts with the Chomskyan postulation of a 
monolithic 'language organ,' the development or 
'growth' of which is controlled largely by the genes. 
Finally, the fact that complex functions can be learned and carried 
out by areas of brain that are innately 'prewired' (if at
all) to do quite different sorts of processing indicates that such 
competences can be and are acquired without any inborn, task-specific
guidance. This is not, of course, to say that language is one of the 
competences that are acquired in this way. For all the current 
evidence shows, many areas of cortex in which language develops may 
indeed be 'prewired' for that task: linguistic nativism 
is still consistent with what is now known. It is, however, to 
suggest that although there may be other reasons to be a linguistic 
nativist, general considerations to do with brain organization or 
development as currently understood give no especial support to that 
position.


### 3.3 The Critical Period for Language Acquisition




Lenneberg (1964, 1967) also argued that although language acquisition
is remarkably robust, in the sense that all normal (and many 
abnormal) children do it, it can occur unproblematically only during 
a 'critical period' -- roughly, up to late childhood
or early puberty. On analogy with other supposedly innately specified
processes like imprinting or visual development, Lenneberg used the 
existence of a critical period as further evidence that language 
possesses a proprietary basis in biology.




In support of the critical period hypothesis about language, 
Lenneberg cited the facts (i) that retarded (e.g., Downs syndrome) 
children's language development stops around puberty; (ii) that 
whereas very young children are able to (re)learn language after 
aphasias produced by massive left-hemisphere trauma (including 
hemispherectomy), aphasias in older children and adults are typically
not reversible; and (iii) that so-called 'wild children,'
viz., those who grow up with no or little exposure to human language,
exhibit severely compromised language skills. (Lenneberg, 
1957:142-55; see Curtiss 1977 for the (in)famous case of Genie, a 
modern-day 'wild child' from suburban Los Angeles, who 
was unable to acquire any but the most rudimentary grammatical 
competence after a miserable and wordless childhood spent locked 
alone in a room, tied to her potty chair or bed.)




As further support for the critical period hypothesis, others have 
added the observation that although children are able to learn a 
second language rapidly and to native speaker fluency, adult learners
of second languages typically are not: the capacity to learn a second
language tapers off after puberty, no matter how much exposure to the
language one has. (Newport 1990). Thus, it was speculated, the 
innate knowledge base for language learning (e.g., knowledge of UG) 
becomes unavailable for normal acquisition at puberty, and adult 
learners must rely on less efficient learning methods. (Johnson and 
Newport 1989.)




As a preliminary to discussing these arguments (many of which are 
presented in more detailed in Stromswold 2000) it is worth 
distinguishing two notions that often get conflated under the name 
'critical period':



> 
> 
> *Critical Period*: a time during development which is 
> *literally* critical; the relevant competence either cannot 
> develop or will be permanently lost unless certain inputs are 
> received during that period.
> 
> 
> 
> *Sensitive Period*: a time during development in which a 
> competence is acquired 'normally,' or 
> 'easily,' or 'naturally.' The competence can 
> be acquired outside the sensitive period, but perhaps less easily and
> naturally, and or perhaps with less ultimate success.
> 
> 
> 




The classic example of a critical period is due to the Nobel 
prize-winning work of Hubel and Wiesel. By suturing shut one of a 
kitten's eyes at various stages of development and for various 
periods of time, Hubel and Wiesel (1970) showed that certain cortical
and thalamic areas supporting binocular vision (specifically, ocular 
dominance 
 columns[20]
 and cells in the lateral geniculate body) will not develop normally 
unless kittens receive patterned visual stimulation during the 4th to
12th weeks of life. They found that while the damage was sometimes 
reversible to some extent, depending on the exact duration and timing
of the occlusion, occlusion for the entire first three months of life
produced irreversible blindness in the deprived 
 eye.[21]





Language, however, is not like this. As we will see, there is little 
evidence for a *critical period* for language acquisition, 
although there is considerable evidence that there is a *sensitive
period* during which language is acquired more easily. The 
implications of this for claims about the innateness of language will
be addressed in SS3.3.4.


#### 3.3.1 Language recovery after trauma




Lenneberg cited the superior ability of children to (re)learn 
language after left brain injury in support of the critical period 
hypothesis. But while there clearly is a difference between the 
abilities of young children, on the one hand, and older children and 
adults, on the other, to recover from left brain insults, the contrast 
in recovery course and outcome is not as stark as is often supposed.




First, older children -- even those who have not succeeded in 
learning language previously -- can substantially recover from 
left hemisphere trauma occurring well after the supposed closure of 
the 'sensitive' or 'critical' period; in 
effect, they learn language from scratch as adolescents. 
Vargha-Khadem *et al*. 1997, for instance, report the case of Alex, 
who failed to speak at all during childhood and whose receptive 
language was at age 3-4 level at age 9. After his left cortex was 
removed at age 9, Alex suddenly began to learn language with gusto, 
and by age 15, his skills were those of an 8-10 year old.




Secondly, most adults suffering infarcts in the left hemisphere 
language areas do in fact recover at least some degree of language 
competence and many recover substantially normal competence, 
especially with treatment (Holland *et al*. 1996). This is thought to 
be due both to the regeneration of damaged speech areas and to 
compensatory development in other areas, particularly in the right 
hemisphere (Karbe *et al*. 1998). Similar processes seem to be at work
in young children with left hemisphere damage. Muller *et al*. 1999, 
for instance, document significant relearning of language, together 
with increased right-hemisphere involvement in language tasks, after 
left-hemisphere lesions in both children (<10) years) and adults 
(>20 years).




Finally, not even very young children are guaranteed to recover 
language after serious insults, whether to the left or right 
hemisphere. As Bates and Roe (2001) argue in their survey of the 
childhood aphasia literature, outcomes differ wildly from case to 
case, and the reported studies exhibit numerous methodological 
confounds (e.g., inability to localize the lesion or to know its 
cause, different measures of linguistic competence, different time 
frames for testing, statistical irregularities, and failure to 
control for other factors known to affect language such as seizure 
history) that cast doubt on the degree of empirical support possessed
by Lenneberg's claim in this instance.


#### 3.3.2 'Wild children'




It has long been recognized that interpretation of the 'wild
child' literature -- helpfully surveyed in Skuse 1993
-- is confounded by the fortunate rarity of these 'natural
experiments,' the generally poor reporting of them, and the
other environmental factors (abuse, malnutrition, neglect, etc.) that
often go along with extreme linguistic deprivation. However, in work
pioneered by Goldin Meadow and colleagues (e.g., Goldin Meadow and
Mylander 1983, 1990), a new population of individuals, who are
linguistically but not otherwise deprived, has begun to be
studied. Deaf but otherwise normal children of hearing parents who are
neither educated in sign language nor sent to special schools for the
deaf do not acquire language, although they usually develop their own
rudimentary signing systems, called 'homesign,' to use
with their families. Studies of what happens to such children after
they are exposed to natural languages (signed or verbal) at various
ages promise to offer new insights into the critical and sensitive
period hypotheses.




At this time, however, there are still very few case reports in the 
literature, and the data so far obtained in these studies are 
equivocal with respect to the sensitive and critical period 
hypotheses. Some adolescents do seem to be able to acquire language 
despite early linguistic deprivation, and others do not. It is 
unclear what the explanation of these different outcomes is, but one 
important factor appears to be whether the new language is a signed 
language (e.g., ASL) or a spoken language. Perhaps because their 
childhood perceptual deficits prevented normal auditory and 
articulatory development, deaf children whose hearing is restored 
later in life do not seem to be able to acquire much in the way of 
spoken language. (Grimshaw *et al*. 1998.)


#### 3.3.3 Second language acquisition in children and adults




The issue of second language acquisition ("SLA") has been
argued to bear on the innateness of language by supporting a critical
(or sensitive) period hypothesis. For instance, Johnson and Newport 
(1989) found that among immigrants arriving in the U.S. before 
puberty, English performance as adults was better the earlier in life
they arrived, but that there were no effects of arrival age on 
language performance for those arriving after puberty. The fact that 
the amount of exposure to the second language mattered for speakers 
if it occurred *before* puberty but not *after,* was 
taken to confirm the critical period hypothesis.




However, these results have failed to be replicated (Birdsong and
Molis 2001) and while it still has its supporters, the 'critical
period' hypothesis regarding second language acquisition is
increasingly being criticized (Hakuta, Bialystok and Wiley 2003;
Nikolov and Djugunovich 2006). Newer studies have argued, for
instance, that the degree of proficiency in a second language
correlates better with, such factors as the learner's level of
educational attainment in that language, her length of residence in
the new country,) and the grammatical similarities between the first
and second languages, and/or length of residence in the new
country. (Flege, Yeni-Komshian and Liu 1999; Bialystok,
1997)[22]




The fact that many adults and older children can learn both first and
second languages to a high degree of proficiency makes clear that 
unlike the kitten visual system studied by Hubel and Wiesel, the 
language acquisition system in humans is not subject to a critical 
period in the strict sense. This finding is consistent with the 
emerging view that the cortex remains highly plastic throughout life,
and that contrary to received wisdom, even old dogs can be quite good
at learning new tricks. (See Buonomano and Merzenich 1998; Cowen and
Gavazzi 1998; Quartz and Sejnowski 1997; and Stiles 2000.) It is 
also consistent with the idea, which seems more plausible 
than the critical period hypothesis, that there is a 
*sensitive* period for language acquisition -- a time, 
from roughly birth age 1 to age 6 or 7, in which language is acquired
most easily and naturally, and when a native-like outcome is 
virtually guaranteed. (Cf. Mayberry and Eichen 1991.) The 
implications of this conclusion for linguistic nativism are examined 
in the next section.


#### 3.3.4 Sensitive periods and innateness: phonological learning




What does the existence of a sensitive period for language mastery
tell us about the innateness of language? In this section, we will
look at a case, namely phonological learning, in which the existence
of a sensitive period has received much press, and in which the
inference from sensitivity to the existence of language-specific
innate information has been made explicitly (see Eimas 1975). One can
argue that even in this case, the inference to linguistic nativism is
weak.




Much rarer than mastery of second language morphology and syntax is 
attainment of a native-like accent, something that first language 
learners acquire automatically in 
 childhood.[23]
 A child's ability to perceive language-specific sounds begins in 
utero, as demonstrated, for instance, by newborns' preference for the
sounds of their mother's voice and their parents' language, and by 
their ability to discriminate prose passages that they have heard 
during the final trimester from novel passages. In the first few 
months of life, babies reliably discriminate many different natural 
language phonemes, whether or not they occur in what is soon to 
become their language. By ages 6 months to 1 year, however, this 
sensitivity to unheard phonemes largely disappears, and by age 1, 
children tend to make only the phonological distinctions made in the 
language(s) they hear around them. For example, Japanese children 
lose the ability to discriminate English /r/ and /l/ (Kuhl *et al*., 
1997b). As adults, people continue to be unable to perceive some 
phonetic contrasts not marked by their language, and many fail to 
learn how to produce even those second language sounds which they can

 distinguish.[24]
 For instance, many English speakers of French have great difficulty 
in producing the French /y/ (as in *tu*) and 
back-of-the-throat /r/.




Thus, in the case of phonological learning, there does seem to be an 
inborn predisposition to segment vocal sounds into language-relevant 
units, or 
 phonemes.[25]
 However, there is also evidence that learning plays a role in shaping
phonological knowledge -- and not just by 'pruning 
away' unwanted 'phonological representations,' as 
Eimas (1975) hypothesized, but also by shaping the precise boundaries
of adult phonemic categories. For example, caregivers reliably speak 
a special 'language' ("Motherese" or 
"Parentese") to young babies, raising pitch, shortening 
sentences, emphasizing stressed morphemes and word boundaries and 
-- most relevant here -- exaggerating the acoustical 
differences between certain crucial vowels (in English, /i/, /a/ and 
/u/) . This 'stretching' of the distance between vowels 
(demonstrated in Finnish and Russian as well as English by Kuhl et 
al. 1997a) facilitates the infant's representation of clearly 
distinguishable vowel prototypes. Kuhl 2000 argues that these 
prototypes subsequently function as 'magnets' around 
which subsequent linguistic experiences are organized, and form the 
set points of the language-specific phonological 'map' 
that emerges by the end of the first year.




If this is indeed how phonological learning works, it is clear that 
while experience clearly plays a role, the inborn contribution to 
that process is quite substantial. For discriminating phonemes 
-- however those discriminations might be shaped by subsequent 
experience -- is no simple matter. It involves what is called 
'categorical perception, that is, the segmenting of a signal 
that varies continuously along a number of physical dimensions (e.g.,
voice onset time and formant frequency) into discrete categories, so 
that signals within the category are counted as the same, even though
acoustically, they may differ from one another more than do two 
signals in different categories (see Fig. 5). (Harnad 1987 is a 
useful collection of work on categorical perception to the 
mid-1980s.)




But is this inborn contribution to phonological learning *language
specific*, that is, does it support the conclusion that (this 
aspect of) language is innate? And to this question, the answer 
appears to be 'No.' First, the 'chunking' of 
continuously varying stimuli into discrete categories is a feature 
not just of speech perception, but of human perception generally. For
instance, it has been demonstrated in the perception of 
non-linguistic sounds, like musical pitch, key and melody, and 
meaningless chirps and bleats (Pastore and Layer 1990). It has also 
been demonstrated in the processing of visual stimuli like faces 
(Beale and Keil 1995), facial expressions (Etcoff and Magee 1992; 
Kotsoni, de Haan and Johnson 2001); facial gender (Campanella, 
Chrysochoos and Bruyer 2001); and familiar physical objects (Newell 
and Bulthoff 2002). Secondly, it is known that other animals too 
perceive categorically. For instance, crickets segment consepecific 
songs in terms of frequency (Wyttenbach, May and Hoy 1996), swamp 
sparrows 'chunk' notes of differing durations (Nelson and
Marler 1989), and rhesus monkeys can recognize melodies when 
transposed by one or two octaves, but not by 1.5 or 2.5 octaves, 
indicating a grasp of musical key (Wright *et al*. 2000). Finally, 
other species respond categorically to human speech! Chinchillas 
(Kuhl and Miller 1975) and cotton-top tamarins (Ramus *et al*. 2000) 
make similar phonological distinctions to those made by human 
infants.




Together, as Kuhl 1994, 2000 argues, these findings cast doubt on 
the language-specificity of the inborn perceptual and categorization 
capacities that form the basis of human phonological learning. For 
given the fact that human (and animal) perception quite generally is 
categorical, it is arguable that languages have evolved so as to 
exploit the perceptual distinctions that humans are able to make, 
rather than humans' having evolved the abilities to make just the 
distinctions that are made in human languages, as a view like Eimas' 
would suggest. 



> 
> ![Categorical Perception Graph](cat-percep.png)
> 
> 
> Figure 5. Note that the pair of sounds circled in blue differ in F2 
> starting frequency less than those circled in red, yet the former are
> both reliably counted as instances of the sounds /b/ whereas the 
> latter are reliably classified as different sounds, /d/ and /g/. This
> pattern, together with the abrupt switch from one classification to 
> another (e.g. /b/ to /g/), is characteristic of categorical 
> perception.
> 
> 
> 




The same may be true in non-phonological domains too. The notion that
at least some of the capacities responsible for syntactic learning 
are non-language specific is suggested by analogous results about the
non-species specificity of recursive rule learning and generalization
-- an ability that Chomsky has recently suggested forms the core
of the human language faculty. (Hauser, Chomsky and Fitch 2002; see 
below, 3.4 for further discussion.) Other species, notably cotton top
tamarins, seem capable of learning simple recursive rules (Hauser, 
Weiss, and Marcus 2002). In addition, Hauser and McDermott 2003 
argue that musical and syntactic processing involve similar 
competences, which are again seen in other species. Together, these 
findings suggest that there are aspects of the human 'language 
faculty' that are neither task-specific nor species-specific. 
Instead, language learning and linguistic processing make use of 
abilities that predate language phylogenetically, and that are used 
in humans and in animals for other sorts of tasks. (See e.g., Hauser,
Weiss, and Marcus 2002 for an account of recent work on rule 
learning by cotton top tamarins; see Hauser and McDermott 2003 for 
the suggestion that aspects of musical and syntactic processing 
involve similar competences, which are again seen in other species.) 
Rather than viewing the human mind as being innately specialized for 
language language learning, it seems at least as reasonable to think 
of languages as being specialized so as to be learnable and usable by
the human mind; of this, more in SS3.4 below.


### 3.4 Language Evolution




This brings us to the question of language evolution: if knowledge of
language (say, of the principles of UG) really is inborn in the human
language faculty, how did such inborn knowledge evolve? For many 
years, Chomsky himself refused to speculate about this matter, 
stating that "[e]volutionary theory...has little to say, 
as of now, about questions of this nature" (1988:167). Other 
theorists have not been so reticent, and a large literature has grown
up in which the selective advantages of having a language are 
adumbrated. It's good for communicating with, for instance, when 
trying to figure out what conspecifics are up to (Pinker and Bloom, 
1990; Dunbar 1996). It's a mechanism of group cohesion, analogous to
primate grooming (Dunbar 1996). It's a non-genetic mechanism of 
phenotypical plasticity, allowing organisms to adapt to their 
environment in non-evolutionary time (Brandon and Hornstein 1986; 
Sterelny 2003). It's a mechanism by which we can bend others to our 
will (Dawkins and Krebs 1979; Catania 1990), or make social 
contracts (Skyrms 1996). Language makes us smarter, perhaps by being
internalized and functioning as a 'language of thought' 
(Bickerton 1995, 2000). And so on.




The ability to speak and understand a language no doubt provided and 
continues to provide us with many of these benefits. Consequently 
(and assuming that the costs were not too great -- as patently 
they weren't), one can be sure that whatever it is about human beings
that enables them to learn and use language would have been subjected
to strong positive selection pressure once it began to emerge in our 
species.




But none of this speaks directly to the issue of linguistic nativism.
The fact that Mother Nature would have favored individuals or groups 
possessing linguistic abilities tells us nothing about the 
*means* she chose to get the linguistic phenotype built. That 
is, it tells us nothing about the sorts of psychological mechanisms 
that were recruited to enable human beings to learn, and subsequently
use, a natural language.




Nativism is, of course, one possibility. Natural selection might have
built a specialized language faculty, containing inborn knowledge 
about language (e.g., knowledge of UG), which subsequently was 
selected for because it helped human children to acquire linguistic 
competence, and having linguistic competence enhanced our ancestors' 
fitness. A problem with this hypothesis, however, is that it is 
unclear how a language faculty containing innate representations of 
UG might have arisen in the human mind. One view is that the language
faculty was built up piecemeal by natural selection. This approach 
underlies Pinker and Bloom's (1990) and Jackendoff's (1999) proposals
as to the adaptive functions of various grammatical features and 
devices. Other nativists, however, reject the adaptationist 
framework. For instance, Berwick 1998, has argued that efforts to 
explain the piecemeal development of knowledge of linguistic 
universals in our species may be unnecessary in light of the new, 
Minimalist conception of syntax (see Chomsky 1995). On this view, 
all parametric constraints and rules of syntax are consequences of a 
fundamental syntactic process called Merge: once Merge was in place, 
Berwick argues, the rest of UG automatically followed. Chomsky, 
taking another tack, has suggested that language is a 
'spandrel,' a byproduct of other non-linguistically 
directed selective processes, such as "the increase in brain 
size and complexity" (1982:23). And finally Bickerton 1998, on 
yet another tack, posits a massive saltative episode in which large 
chunks of syntax emerged all at once, although this posit is 
implicitly withdrawn in Calvin and Bickerton 2000.




The literature on language evolution is too large to survey in this 
article (but see Botha 2003 for an excellent overview and critique).
Suffice it to note that as yet, no consensus has emerged as to how
 innate knowledge of UG might have evolved from 
whatever preadaptations existed in our ancestors. Of course, this is 
not in itself a problem for linguistic nativists: formulating and 
testing hypotheses about human cognitive evolution is a massively 
difficult enterprise, due largely to the difficulty of finding 
evidence bearing on one's hypothesis. (See Lewontin 1998 and Sterelny
2003:95-116.)




It's worth noting, however, that linguistic nativism is just one 
possibility for how Nature got language up and running. Just as it 
may be that a language faculty embodying knowledge of UG was somehow 
encoded in the human genome, it's also possible that that our ability
to learn a language is based on a congeries of pre-existing 
competences, none of which is (or was initially -- see below) 
specialized for language learning. Tomasello's theory of language 
acquisition, discussed above (SS2.2.1.b), invites this 
alternative evolutionary perspective. On his view, the fundamental 
skills with which linguistic competence is acquired are skills that 
originally served, and still continue to serve, quite different, 
non-linguistic functions. For example, he argues that children's 
early word and phrase learning rest in part on their ability to share
attention with others, to discern others' communicative intentions, 
and to imitate aspects of their behavior. There is reason to think 
that these abilities evolved independently of language, at least 
initially: imitation learning enabled the fast and high-fidelity 
transfer of learned skills between generations (see Tomasello 1999, 
2000) and the ability to form beliefs about the mental states of 
others ('mind-reading' or 'theory of mind') 
enabled highly intelligent animals, such as our hominid ancestors, to
negotiate a complex social environment made up of similarly 
intelligent conspecifics. (See, e.g., Sterelny 2003.) On this sort 
of view, the ability to learn language piggy-backed on other 
capacities, which originally evolved for other reasons and which 
continue to serve other functions in addition to their linguistic 
ones.




You might wonder, however, whether this latter kind of account really
differs substantively from that of a nativist. Assuming that she does
not reject adaptationism altogether, the nativist will presumably be 
committed to the idea that the innate language organ, or faculty 
embodying knowledge of UG, was derived from pre-existing structures 
that were either functionless or had non-linguistic functions. These 
structures subsequently acquired linguistic functions through being 
selected for that reason: they became adaptations for language. But 
so too would the various capacities postulated by Tomasello. As soon 
as they started being used for language learning, that's to say, they
would have been selected for that function (in addition to any other 
functions they might serve, and always assuming that linguistic 
abilities were on balance beneficial). Hence they too will over time 
become adaptations for language. On both Tomasello's and the 
nativist's view, in other words, the inborn structures responsible 
for language acquisition will have acquired the biological function 
of enabling language acquisition: they will be specialized for that 
purpose. Is Tomasello, then, a nativist?




No. First, even though the psychological abilities and mechanisms 
that Tomasello posits have been selected for linguistic functions, 
these abilities and mechanisms have continued to be used (and, 
plausibly, selected) for non-linguistic purposes, such as face 
recognition, theory of mind, non-linguistic perception, etc. So, 
whereas a central tenet of linguistic nativism is its insistence that
the structures responsible for language learning are 
*task-specific*, Tomasello sees those structures as being much
more general-purpose. In addition, and this is a second reason not to
count Tomasello as a nativist, the inborn structures he posits are 
not plausibly interpreted as containing any kind of language specific
information or representations. Yet a commitment to the role of 
inborn, language-specific information (such as knowledge of UG) is 
another hallmark of linguistic nativism.




Several theorists (e.g., Clark 1996, Tomasello 1999, and Sterelny, 
2003) have stressed that in addition to working on human linguistic 
abilities directly, via changes to the parts of the genome coding for
those abilities, natural selection can also bring about such changes 
indirectly, by making sure that our minds are embedded in certain 
kinds of environments. All sorts of animals create environments for 
themselves: this is called 'niche construction.' (The 
term is due to Odling-Smee, Laland and Feldman 1996.) Many animals 
also (or thereby) create environments for their offspring as well. 
And as Odling-Smee *et al*. 1996, Avital and Jablonka 2000, and 
Sterelny 2003 stress, animals' dispositions to modify the 
environments of both themselves and their offspring in certain ways 
are just as much potential objects of selection as are other of their
traits.




To see this, suppose that an organism O has a genetically encoded 
disposition N to build a special kind of nest; suppose further that 
being raised in this kind of nest causes O-type offspring to have 
characteristic C; and suppose finally, that Os with C enjoy greater 
reproductive success than those without. Then, assuming that there is
variation in N in the population, natural selection can operate so as
to increase the proportion of Os with N -- and hence also those 
with characteristic C -- in the population. Down the track, Os 
will have C not by virtue of acquiring a special, genetically-encoded
disposition-for-C. Rather, they will have C because their parents 
have the genetically-encoded disposition N, and Os whose parents have
N 'automatically' develop C.




This toy example illustrates a further route by which language might 
have evolved in human beings. In addition to creating inborn 
language-learning mechanisms in individuals, natural selection may 
also have created dispositions to construct particular kinds of 
linguistic learning environments *in their* *parents*. 
For example, as Clark (1996) and Sterelny (2003) both speculate, 
Mother Nature might have worked on our dispositions to use 
'Motherese' to our children, and/or on our tendency to 
talk about things that are current objects of the child's perceptual 
attention, in order to create learning environments conducive to the 
acquisition of language.




In principle, the existence of this sort of 'niche
construction' can be accepted by all parties to the nativism
controversy. That is, both Tomasello and Chomsky could agree that
dispositions to construct 'linguistic niches' --
environments in which languages are easy for human offspring to learn
-- may have been selected for in our species. Nevertheless, the
notion of niche construction militates against the nativist,
particularly when one takes into account the related notion of
'cumulative downstream niche construction.'




Cases of what Sterelny (2003: 149ff) calls 'cumulative 
downstream niche construction' occur when a generation of 
animals modifies an environment that has already been modified by 
earlier generations. A mountain thornbill's nest is an instance of 
downstream niche construction (since its offspring are affected by 
the thornbill's efforts). However, the construction is not 
cumulative, since the nest is built anew each year. By contrast, a 
rabbit warren extended and elaborated over several generations is an 
instance of cumulative construction: successive generations of 
offspring inherit an ever-more-complex niche and their other 
behaviors are tuned accordingly in ever-more-complex ways. Tomasello,
1999 and Sterelny 2003 stress that niche construction, including 
downstream niche construction, is not limited to the physical world: 
animals make changes to their social and epistemic worlds as well. 
For instance, chimpanzees live in groups (= construction of a social 
niche) and dogs mark their territory (= a change in their epistemic 
niche, relieving them of the necessity of remembering where the 
boundaries of their territory are). Humans, says Sterelny, echoing a 
theme of Tomasello 1999, are niche constructors "with a 
vengeance" (2003:149) and many of the changes they make to 
their physical, social and epistemic environments accumulate over 
many generations (think of a city, a democracy, modern science, a 
natural language). Such cumulative modifications allow for what 
Tomasello calls a "ratchet effect": a "cycle in 
which an improvement is made, becomes standard for the group, and 
then becomes a basis for further innovation." (Sterelny 2003: 
150-1)




The idea of cumulative niche construction has obvious application to 
the case of language. If parents shape the linguistic environment of 
their offspring, and if we all shape the linguistic environments of 
our conspecifics (merely by talking to them!) then the possibility of
a 'linguistic ratchet effect' is clearly open. Small 
changes made to the language of the group by one generation -- 
changes which perhaps make it easier to learn, or easier to 
understand or produce -- will be transmitted to later 
generations, who may in turn make further changes geared to 
increasing language learnability and ease of use. This scenario 
raises the possibility, already mentioned at the end of the last 
section, that language may have evolved so as to be learnable and 
usable by us, in addition to the converse scenario (stressed in much 
work on the evolution of language) that *we* had to change in 
many and complex ways in order to learn and use a language. Thus, we 
might speculate, languages' phonetic systems evolved so as to be 
congenial to our animal ears; their expressive resources (in 
particular, their vocabularies) evolved so as to fit our 
communicative needs; and perhaps, as Clark 1997 has suggested and as 
Tomasello 2003 implicitly takes for granted, natural language syntax
evolved so as to suit our pre-existing cognitive and processing 
capacities. To be sure, the languages we have coded in our heads look
complex and weird to linguists and psychologists and philosophers who
are trying to put together theories about them. But, if languages and
human minds have evolved in tandem, as surely they have, then 
languages may not look weird at all from the point of view of the 
brains that implement and use them.




All of these processes have likely played a role in the evolution of
our capacities to learn and use a natural language. Pre-existing
psychological, perceptual and motor capacities would have been
recruited for the task of language learning and use. These capacities
would have been honed and specialized further by natural selection for
the performance of linguistic tasks. The functions of some of them,
perhaps, would have become so specialized for language-related tasks
that they cease to perform any non-linguistic functions at all --
and to this extent, perhaps, linguistic nativism would be
vindicated. At the same time, however, language itself would have been
evolving so as the better to suit our cognitive and perceptual
capacities, and our communicative needs. Given the fact that many
different perceptual, motor and cognitive systems are implicated in
language use and learning, and given the co-evolution of our minds and
our languages, the truth about language evolution, when it emerges, is
unlikely to be a simple. For this reason, it is unlikely to
vindicate the nativist's notion that a specialized and monolithic
'language organ' or 'faculty' is at the root
of our linguistic capacities.




Before leaving the question of language evolution, it is necessary to
mention a recent paper by Hauser, Chomsky and Fitch 2002 on this 
topic. First, they distinguish (2002:1571) what they call the 
'faculty of language in the narrow sense,' or 
'FLN,' from the 'faculty of language in the broad 
sense,' or 'FLB.' The FLN is the "abstract 
linguistic computational system alone...which generates internal
representations and maps them into the sensory-motor interface by the
phonological system, and into the conceptual-intentional interface by
the (formal) semantic system." (*Ibid.)* The FLB 
includes the FLN plus all the other systems (motor systems, 
conceptual systems, perceptual systems, and learning skills) which 
contribute to language acquisition and use.




Next, Hauser *et al*. speculate that the only thing that's really 
special about the human FLB is the FLN. That is, with the exception 
only of the FLN, FLB comprises systems that are shared with (or only 
slight modifications of) systems in other animals. Consequently, 
there is no mystery (or no more mystery than usual) about how these 
language-related abilities evolved. FLN, on the other hand, is 
distinctive to humans and what is special about it is its power of 
*recursion*, that is, its ability to categorize linguistic 
objects into hierarchically organized classes, and (on the behavioral
side) for the generation of infinitely many sentences out of finitely
many words. According to Hauser *et al*., the only real evolutionary 
mystery about language is how this capacity for recursion evolved 
-- and this question, argue Hauser *et al*, is eminently 
addressable by normal biological methods (e.g., comparative studies 
to determine possible precursor mechanisms, etc.).




However, there are two difficulties with this scenario. First, there 
is evidence that the power of recursion posited by Hauser *et al*. as 
being distinctive of the human FLN is in fact not distinctive to 
humans, because it is not species specific. (See Esser, *et al*. 1997
and McGonigle, Chalmers and Dickinson, 2003.) Second, 
recursiveness is not language specific either, but is a feature of 
other domains of human cognition and endeavor as well. Our conceptual
space, for instance, appears to be hierarchically ordered (poodles 
are a kind of dog, which are a kind of quadruped, which are a kind of
animal, etc.). Similarly, the planning and execution of 
non-linguistic actions seems often to involve the sequencing and 
combining of smaller behavioral units into larger wholes. Recursion 
might well be an important part of the human language faculty, but 
it's apparently not specific either to us or to that faculty. Or, to 
put the point more bluntly: if it's Chomsky's view that recursiveness
is the pivotal feature of the language faculty, and if recursiveness 
is a feature of human cognition and action more generally, then it's 
not clear that Chomsky remains a linguistic 
 nativist.[26]



### 3.5 Pidgins and Creoles




It has been argued (by, e.g., Bickerton 1981, and Pinker, 
1994:32-9) that the process by which a pidgin turns into a creole 
provides direct evidence of the operation of an innate language 
faculty. Pidgins are rudimentary communication systems that are 
developed when people speaking different languages come together 
(often in a commercial setting or when one people has conquered and 
is exploiting another) and need to communicate about practical 
matters. Creoles arise when pidgins are elaborated both syntactically
and semantically, and take on the characteristics of *bona 
fide* natural languages.




Bickerton and, following him, Pinker, argue that creolization occurs 
when children take a pidgin as the input to their first language 
learning, and urge that the added complexity of the creole reflects 
the operation of the child's inborn language faculty. Moreover, they 
argue, since creole languages all tend to be elaborated in the same 
ways, and since they all respect the constraints of UG, the 
phenomenon of creolization also supports the idea that the inborn 
contribution to language acquisition is not just some general drive 
for an effective system of communication, but rather knowledge of 
linguistic universals.




There are two problems with this 'language bioprogram 
hypothesis,' as it is known in the creolization literature. The
first concerns the claim (e.g., Bickerton 1981:43-70) that even 
creoles that developed in quite different areas of the world, and in 
complete isolation from one another, bear "uncanny 
resemblances" (Pinker 1994:25) to each other, not just in 
respecting the constraints of UG, but -- even more surprisingly 
-- in using fundamentally the same means to elaborate their root
pidgins (e.g., in using the same syntactic devices to mark tense, 
aspect and modality). The stronger claim made by Bickerton -- 
that Creoles use the same devices for the same grammatical purposes 
-- is simply not true. For example, as Myhill (1991) argues, 
Jamaican Creole, Louisiana Creole, Mauritian Creole and Guyanese 
Creole mark tense, aspect and modality in ways that are quite 
different from those that Bickerton (1981) proposed as universal. 
(See, however, Mufwene 1999 for a case that confirms Bickerton's 
predictions.) The weaker claim -- that creoles respect the 
constraints imposed by UG -- has not, so far as I know, been 
contested. So we will assume, in what follows, that creoles, like 
other NLs, respect UG. The important question for our purposes is: 
how does this come about?




The bioprogram hypothesis claims that creolization occurs as a result
of the action of the language faculty: children who learn language 
from degraded (e.g., pidgin) inputs are compelled by their innate 
knowledge of grammar to produce a fully-fledged natural language (the
creole) as output. As an example of how children add UG-constrained 
structure to languages learned from degraded inputs, Pinker cites the
case of Simon, a deaf child studied by Newport and her colleagues, 
who learned American Sign Language (ASL) from parents who themselves 
were not exposed to ASL until their late teens. Although they used 
ASL as their primary language, Simon's parents were "in many 
ways...like pidgin speakers," says Pinker (1994:38). For 
instance, they used inflectional markers in an inconsistent way and 
often failed to respect the structure-dependence of the rules 
governing topicalization in that 
 language.[27]
 But "astoundingly," says Pinker, "though Simon saw 
no ASL but his parents' defective version, his own signing was far 
better ASL then theirs...Simon must somehow have shut out his 
parents' ungrammatical 'noise.' He must have latched on 
to the inflections that his parents used inconsistently, and 
interpreted them as mandatory." (1994:39) Pinker views this as 
a case of "creolization by a single living child" 
(*ibid.*) and explains Simon's conformity to ASL grammar in 
terms of the operation of his innate language faculty during the 
acquisition period.




In a recent overview of the Simon data from the last 10 or so years, 
however, Newport 2001, stresses a number of facts that Pinker's 
presentation obscures or downplays. First, Simon's performance was 
not that of a native signer, although he did develop "his own 
version of ASL whose structure was more like that of other natural 
languages [than that of his parents' ASL]" (Newport 2001:168).
For instance, Simon's morphology stabilized at a level that was 
"not as complex as native ASL" and he didn't acquire 
standard classifier morphemes if they were not used by his parents 
(*ibid.*). Secondly, Simon's success in learning a given rule 
seemed to vary with how well or badly his parents signed. For 
instance, Simon's parents used the correct inflectional morphology 
60-75% of the time for a large class of verbs of motion, and in this 
case, Simon's own use of such morphology was 90% correct. However, 
some members of the class of classifier morphemes were correctly used
by the parents only 40% of the time, and in this case, although 
Simon's performance was better than his parents', it was not at 
native signer level.




Newport argues that Simon appears to be 'cleaning up' his
parents' language, that is, "bas[ing] his learning heavily on 
his input, but reorganiz[ing] this input to form a cleaner, more 
rule-governed system than the one to which he was exposed." 
(2001:168) She agrees that this result could be due to constraints 
imposed by an innate language faculty, but argues that it is also 
consistent with the existence of some more generalized propensity in 
children to generate systematic rules from noisy inputs, rightly 
pointing out that the latter hypothesis cannot be ruled out in 
advance of empirical test. (In this context, she notes (p.170) some 
preliminary studies suggesting that inferring systematic rules from 
messy data may indeed be a more general feature of learning in young 
children (though, interestingly, not in adults), for they can be seen
to exhibit this tendency in non-linguistic pattern-learning contexts 
too.) Newport concludes that "the contrasts between Simon and 
his parents are in certain ways less extreme, and more 
reorganizational, than might be suggested by the Language Bioprogram 
Hypothesis...[H]e does not appear to be creating an entirely new
language from his own innate specifications; rather, he appears to be
following the predominant tendencies of his input, but he sharpens 
them, extends them, and forces them to be internally 
consistent." (2001:173).




If Newport *et al*. are right, the case of Simon does not seem to give 
much support to the nativist hypothesis. Moreover, the argument from 
creolization suffers a number of additional flaws. First, the 
Bickerton-Pinker view, which assigns a dominant role to child 
language learners in the creation of creoles, is but one of three 
competing hypotheses currently being explored in the creolization 
literature. According to the 'superstratist' hypothesis, 
creolization occurs not when children acquire language from pidgins, 
but when successive waves of adult speakers try to learn the language
of the dominant culture as a second language. (Chaudenson 1992, for 
instance, defends this view about the origins of French creoles.) On 
this view, the additional devices seen in creoles are corruptions of 
devices seen in the dominant language. According to the 
'substratist' hypothesis, creoles are again created by 
second language learners, rather than children, only the source of 
added structure is the first language of the learner. (Lumsden 1999 
argues that numerous traces of a variety of African languages in 
Haitian creole support this hypothesis.) One need not take a stand on
which of these views is correct in order to see that these competing 
explanations of creolization undermine Bickerton and Pinker's 
'bioprogram' hypothesis. If creoles arise out of the 
attempts of adult learners to learn (and subsequently pass on to 
their children) another, non-native language, then what one might 
call 'contamination of the stimulus,' rather than the 
influence of an inborn UG in the learner, is what accounts for the 
UG-respecting ways in which creoles are elaborated.




However, there is a case of creolization in which these other 
hypotheses apparently fail to gain purchase, as Pinker (1994:37ff.) 
emphasizes. This is the case of the development of Idioma de Signos 
Nicaraguense (ISN, Nicaraguan Sign Language), a brand-new 
natural sign language which first emerged around 30 years ago in 
schools for the deaf in and around Managua. These schools were first 
set up in the 1970s, and ISN evolved from the hodge-podge of homesign
systems used by students who entered the schools at that time. ISN is
an interesting test case of the bioprogram hypothesis for two 
reasons. First, homesign systems are idiosyncratic and possess little
syntactic structure: the natural-languagelike syntax of ISN could 
therefore not derive from substrate influence. And Spanish, the only 
potential candidate for superstrate influence was allegedly 
inaccessible to signers because of its auditory modality. Pinker 
claims that ISN provides another example of creolization and the 
workings of the innate language faculty: it is 
"created...in one leap when the younger children were 
exposed to the pidgin singing of the older children." 
(1994:36-7)




In their discussion of the development of ISN, however, Kegl, Senghas
and Coppola (1999) show that things are not quite this 
straightforward. ISN did not develop 'in one leap,' from 
the very rudimentary homesigns or 'Mimicas' spoken by 
individual deaf students. Instead, its evolution was more gradual and
was preceded by the creation of what Kegl *et al*. call "Lenguage
de Signos Nicaraguense" (LSN), a kind of "pidgin or 
jargon" (181) that "developed from the point when these 
homesigners came together in the schools and began to share their 
homesigns with each other, quickly leading to more and more shared 
signs and grammatical devices" (180). In addition, the signers 
had access to Spanish language dictionaries, and their language was 
also influenced by the signing of Spanish-speaking, non-deaf teachers
at the schools -- signing which likely incorporated such 
grammatical devices of the teachers' language as were transferable to
a non-vocal medium. (K. Stromswold, private communication.)




While Kegl *et al*. endorse the language bioprogram hypothesis that ISN
emerged 'in one leap,' in the minds of children exposed 
to degraded Mimica or LSN inputs, their data are equally consistent 
with the idea that ISN developed more gradually by means of 
successive elaborations and innovations among a community of 
highly-motivated (because language-starved) young users. Indeed, as 
Kegl *et al*. themselves describe the history (p.187), this is 
precisely what happened. First, a group of signers, each with his or 
her own idiosyncratic form of Mimicas, entered the schools. Members 
of this group gained in expressive power as their individual Mimicas 
were enriched by borrowings from others' homesign systems. Then, a 
new cohort of Mimicas signers entered the schools. Their sign systems
benefitted both from exposure to the Mimicas of their peers and from 
exposure to the richer system developed by the earlier group. Through
a process of successive elaborations in this manner, LSN developed 
and then, by a similar series of steps, ISN developed. At present, 
all three sign systems are still being used in Nicaragua, presumably 
reflecting the different ages at which people are exposed to language
and the kinds of inputs (ISN or LSN vs. signed and written Spanish or
lipreading in regular schools) they receive. In addition, ISN and to 
a lesser extent LSN are still constantly changing -- as one 
would expect if ISN were a community-wide work in progress, not the 
finished product of an individual child's mind,


### 3.6 Developmental Language Disorders and the Search for 'Language Genes'




Dissociations of language disorders acquired in adulthood (e.g., 
Broca's and Wernicke's aphasia) may tell us something about how 
language is organized in the mature brain, but cannot tell us much 
about how language is acquired or the role of innate knowledge in 
that process -- a fact that nativists about language generally 
acknowledge. By contrast, language dissociations arising during 
childhood are sometimes held to bear strongly on the question of 
whether language is innate. Pinker (1994:297-314) articulates this 
latter line of thought, arguing that there is a double dissociation 
between 'general intelligence' and language in two 
developmental disorders called Williams Syndrome (WS) and Specific 
Language Impairment (SLI). People with WS have IQs well below the 
normal range (50-60), yet are able to speak fluently and engagingly 
about many topics. Those with SLI, by contrast, have normal 
([?]90) non-verbal intelligence but speak effortfully and slowly,
frequently making errors in their production and comprehension of 
sentences and words. Pinker argues that there is a double 
dissociation here, and that it supports the view that there is a 
special 'language acquisition device' that is separable 
from any general learning abilities children might possess. In 
addition, following Gopnik 1990a,b, and Gopnik and Crago 1991, he 
urges that the fact that the dissociation appears to concern aspects 
of syntax in particular indicates that the language faculty in 
question is the grammar faculty. Finally, and again following Gopnik,
he argues that since SLI appears to run in families and, in at least 
one case, displays a Mendelian inheritance pattern, what we have here
is evidence not just of a 'grammar faculty,' but of a 
'grammar gene.'


#### 3.6.1 Williams Syndrome




WS is a rare genetic disorder with a complex phenotype. Physically, 
WS individuals display dismorphic facial features, abnormal growth 
patterns, gastrointestinal problems, early puberty, neurological 
abnormalities (including hypotonia, hyperreflexia, hyperacuisis and 
cerebellar dysfunction), defective vision and eye development, bad 
teeth, connective tissue abnormalities, and heart problems. 
Psychologically, in addition to their low non-verbal IQ and 
comparatively spared language abilities, they display relatively good
audiovisual memory but very impaired visual-spatial abilities, 
leading to difficulties in daily life (e.g., getting dressed). They 
have outgoing personalities and are highly sociable to the point of 
overfriendliness, but also display numerous behavioral and emotional 
problems (especially hyperactivity and difficulty concentrating in 
childhood, and anxiety in later life). (Morris and Mervis 2000; 
Mervis *et al*. 2000.)




As to their language, there is currently a debate in the literature
with regard to its normalcy. According to one point of view, the
linguistic competence of WS individuals is remarkably normal,
especially in comparison with that of similarly retarded individuals,
such as those with Downs syndrome (Pinker 1994, 1997; Clahsen and
Almazan 1998; Bello *et al*. 2004; Bellugi *et
al*. 1998). While rather unusual in their choice of words (e.g.,
producing *chihuahua, ibis* and *condor* in addition to
more usual animal words in a word fluency test) and despite
an excessive use of cliches and social stock-phrases, their
ability to use language, especially in conversational contexts, is
more or less intact. For example, they may appear relatively normal in
social interactions, and their processing of conditional questions and
ability to repeat sentences with complex syntax is closer to that of
normal controls than to matched Downs syndrome controls
(Bellugi *et al*. 2000: 13, 15).




According to another school of thought, however, the language 
abilities of WS subjects might be more normal than those of Downs 
syndrome individuals, and might look remarkable in contrast to their 
own marked disabilities in other areas, but nonetheless display a 
number of abnormal characteristics across a variety of measures when 
investigated further. WS language shows "massively 
delayed" early acquisition, especially of vocabulary (Bellugi 
*et al*. 2000:11) and grammatical morphemes (Caprirci *et
al*. 1996); overregularization of regular plural and past tense
endings as well defective competence with regard to irregular nouns
and verbs (Clahsen and Almazan 2001); "inordinate difficulty
with morphosyntax" (Morris and Mervis 2000: 467; see also
Volterra *et al*. 1996; Karmiloff-Smith *et al*. 1997;
Levy and Hermon 2003); and impaired mastery of relative clause
constructions (Grant *et al*., 2002), embedded sentences, and
(in French) grammatical gender assignment (Karmiloff-Smith *et
al*. 1997). Indeed, Bellugi *et al*., 2000, found that WS
children's performance on a sentence-repetition task was
indistinguishable from that of matched controls diagnosed with
Specific Language Impariment, or SLI (see below, SS3.6.2).
Findings such as these lead experts such as Annette Karmilloff-Smith
to urge "dethroning the myth" of WS' "intact"
syntactic abilities (Karmiloff-Smith *et al*. 2003) and move
Ursula Bellugi -- formerly a proponent of the 'spared
language' viewpoint -- to caution that "because their
language abilities are often at a level that is higher than their
overall cognitive abilities, individuals with WMS might be perceived
to be more capable than they really are." (Bellugi *et
al*. 1999.)




In contrast to its cognitive profile, which is, as we have seen, a 
subject of debate, the genetic basis of WS is known. It results from 
a [?]1.5 Mb deletion encompassing the elastin gene ELN at 
chromosome 7q11.23; most cases appear to be due to new mutations. ELN
is crucial in synthesizing elastin, a protein which holds cells 
together in the elastic fibers found in connective tissues throughout
the body and in especially high concentrations in cartilege, 
ligaments and arterial walls. Failure to synthesize this protein 
disrupts development in numerous ways, from the first trimester 
onwards, and gives rise through processes that are not well 
understood to the raft of symptoms associated with the syndrome. 
(Morris and Mervis 2000; Mervis *et al*. 2000.)


#### 3.6.2 Specific Language Impairment




In contrast with Williams syndrome, in which one sees comparatively 
spared language in the face of mild to moderate mental retardation 
and numerous physical defects, specific language impairment 
('SLI') is diagnosed when (i) non-verbal intelligence as 
measured by standard IQ tests is normal; (ii) verbal IQ is well below
normal; and (iii) obvious causes of language impairment (e.g., 
deafness, frank neurological damage) can be ruled out. As one might 
expect given these diagnostic criteria, a diagnosis of SLI embraces a
highly heterogeneous collection of language-related deficits, not all
of which co-occur in every case of language impairment. (Bishop, 
1994; Bishop *et al*,. 2000.) These include:


* productive and receptive phonological deficits (e.g., difficulty
producing clusters of consonants, as in *spectacle,* and
failure to show categorical perception of phonemes differentiated by
place of articulation (/ba/ vs. /ga/) and voicing (/ba/ vs. /pa/);
* morphological deficits (e.g., generation of past tenses or plurals
by using affixes);
* productive and receptive syntactic deficits (e.g., analyzing
'reversible' passives (*Katie kissed Jacob*
vs. *Jacob was kissed by Katie*), complex dative constructions
(e.g., *Katie gave Jacob the book*) and anaphora (e.g.,
*Katie said that Sarah scratched her* vs. *Katie said that
Sarah scratched herself)*.




As a consequence of this heterogeneity, SLI, researchers have 
introduced a number of subtypes of the disorder, including such 
things as 'Verbal auditory agnosia,' 
'Lexical-syntactic deficit syndrome' and 
'Phonological programming syndrome' (Bishop 1994). Also 
as a consequence, and in part because studies do not always 
distinguish between different subtypes, the etiology of SLI in 
general is not well understood (O'Brien *et al*. 2003), although 
recent research suggests at least two distinct genetic loci are 
involved in at least some subtypes of the disorder (Bishop 2006). 
Some posit an underlying defect in the 'grammar module.' 
For instance, Rice and Wexler (1996) attribute SLI individuals' 
morphological deficits to a missing UG principle, namely, the 
principle of inflection, and Van der Laly and Stollwerk 1997, 
attribute some SLI children's difficulty with anaphora to their 
failure to acquire Binding Theory. Others see non-linguistic defects,
such as auditory, memory or processing deficits as the root problem. 
For instance, Tallal 1980, 1985 argue that many SLI cases result 
from deficits in the processing of rapid auditory stimuli, giving 
rise to a failure to learn to distinguish phonemes correctly, which 
in turn leads to a failure to acquire other aspects of grammar. 
Others, such as and Norbury, Bishop and Briscoe 2002 argue that such 
children's limited processing capacities are the culprit.




While the varied symptomatology of SLI suggests that no unified 
theory of its etiology might be forthcoming, the cause of the 
disorder is comparatively well understood in the case of one subtype,
involving a severe disruption of morphosyntax (i.e., the rules 
governing the formation of words from smaller semantic units, or 
morphemes). This subtype, seen in about half the members of a large, 
three-generation English family, the KE's, and in another, unrelated 
individual, has been traced to a specific genetic mutation, the 
function of which is actively under investigation.




The KE family has received much press since the early 1990s, when 
Gopnik 1990a,b and Gopnik and Crago 1991 (see also Gopnik 1997) 
proposed that their morphosyntactic deficits were caused by a 
mutation in a single dominant gene normally responsible for the 
encoding of grammatical features, such as function words and the 
inflections used to mark number, tense, aspect, etc. According to 
Gopnik, the affected KE's are 'feature blind' as a 
consequence of this mutation. And according to Pinker (1994), their 
pedigree (Fig. 6) and specifically morphosyntactic deficits 
constitutes "suggestive evidence for grammar genes ... 
genes whose effects seem most specific to the development of the 
circuits underlying parts of grammar" (Pinker 1994:325).



> 
> ![KE Diagram](KE.jpg)
> 
> 
> Figure 6. The KE family pedigree  
>  
>  (*Image used by permission of Simon E. Fisher*)
>  
> 
> 
> 




Other intensive studies of the KE family, by Vargha-Khadem and
colleagues (e.g., Vargha-Khadem *et al* 1995, 1998;
Watkins *et al*., 2002) have vigorously disputed the hypothesis
that the root cause of the KE's language disorder is a syntactic
deficit. Instead, they argue, the KE phenotype is much broader than
Gopnik's account suggests, and their 'feature blindness'
is merely one among the many effects of an underlying articulatory
problem. As characterized by Vargha-Khadem's team, the affected KE's
speech is effortful, "sometimes agrammatical and often
unintelligible" (Watkins *et al*. 2002:453), and shows
impairments not just in morphosyntax (e.g., regular plural and past
tense endings) but also in the formation of irregular past tenses
(where correct usage is lexically determined, rather than
rule-governed) and in sentence-level syntax, particularly word order.
Comprehension, too, is impaired at the level of syntax as well as
words, and as is their reading of both words and non-words. These
results indicate that the KE's problems go beyond morphosyntax, and
the fact that affected KE's have significantly lower non-verbal IQs
(by 18-19 points; Vargha-Khadem *et al*. 1995) than unaffected
family members indicates that their deficits may be further reaching
 still.[28]
 Finally, affected KE's have trouble sequencing and executing
non-language-related face, mouth and tongue movements and show
abnormal activation not just of speech but also of motor areas on fMRI
scans (Liegeois, *et al*. 2003); this deficiency in
'orofacial praxis' supports Vargha-Khadem's hypothesis
that the root problem for the KE's is articulatory.




As Gopnik noted, the pattern of inheritance in the KE family suggests
that a single, dominant gene is responsible for the disorder. (See
fig. 6) In the early 1990's, Fisher and colleagues began working to
isolate the gene. First, it was localized to a region on chromosome
7q31 containing about 100 genes (Fisher *et al*. 1997, 1998;
O'Brien *et al*. 2003). Later, it was identified (Lai *et
al*. 2001; Fisher et al. 2003) as the gene FOXP2, which encodes a
regulatory protein or 'transcription factor' (i.e., a
protein that helps to regulate the rate of transcription of other
genes in the genome -- in the case of FOXP2, the protein acts to
inhibit transcription of the downstream gene(s)). In affected family
members, a single base-pair substitution in the gene coding for this
regulatory protein leads to the insertion of the amino acid arginine
(instead of the normal histamine) in an area of the protein (viz., the
'forkhead binding domain') that is critical for its
ability to modulate the transcription of the downstream DNA. As a
consequence, FOXP2 cannot perform its normal regulatory role in
affected KE family members.




The failure of FOXP2 to perform its normal role in turn leads to
abnormal brain development in affected KE individuals. Studies of
other animals and humans (e.g., Lai *et al*. 2003;
Takahashi *et al*., 2003; Ferland *et al*. 2003;
Teramitsu *et al*. 2004) show that FOXP2 is normally highly
expressed in both development and adulthood in two distinct brain
circuits, One is a corticostriatal circuit, in which inputs from the
prefrontal and premotor cortex are modulated by the basal ganglia and
the thalamus, and then sent back to prefrontal and premotor cotical
areas; the other is an olivocerebellar circuit, in which sensory input
is sent via the spinal cord for processing in the medulla, cerebellum
and thalamus before being handed on to prefrontal cortex. (See
fig. 7.) The basal ganglia are known to be involved in the sequencing
and reward-based learning of motor behaviors (Graybiel 1995, 1998),
and the cerebellar circuit, while less well understood, is thought to
be a proprioceptive circuit involved in motor regulation and
coordination (Lieberman 2002). FOXP2 is expressed in homologues of
these areas in other species (e.g., canaries, zebra finches, rats) and
in all species studied, these areas are involved in motor sequencing
and coordination (Sharff and White 2004).



![Figure 7](foxp2.png)




Figure 7. Two circuits in which FOXP2 is expressed. (Based on figures
by Diana Weedman Molavi, The Washington University School of Medicine

 Neuroscience Tutorial).
 




So, what appears to be the case is that affected KE family members' 
language difficulties result from a mutation in the FOXP2 gene, which
results in abnormal development of the striatal, cerebellar and 
cortical areas necessary for the sequencing and coordination of 
speech-related movements of the mouth, tongue and possibly larynx; 
MRI scans of affected family members showing reduced gray matter 
density in these areas support this hypothesis, as do fMRI scans 
showing abnormal striatal and cortical activation during receptive 
and active language processing (Belton *et al*. 2003; Liegeois, et 
al. 2003.)




Vargha-Khadem speculates (cf. Watkins *et al*. 2002:463) that those of
the KE's deficits that do not appear to be motor related (e.g., their
comprehension and reading problems, their difficulties with word 
order and syntax) are a result of impaired learning that itself 
results from their motor deficits. For instance, impaired 
articulation could lead to impoverished phonological representations,
which would then impair the acquisition of morphological and 
morphosyntactic knowledge, which would then constitute a poor basis 
for further syntactic learning. Impaired representation at all of 
these levels would then express itself in receptive language and 
reading, as well as in the realm of spoken language. Another possible
explanation of the KE's non-articulatory deficits, which is not 
necessarily in competition with the previous one, derives from the 
fact that the basal ganglia are also known to be implicated in 
working memory (Bosnan 2004) and reward-based learning (e.g., 
classical conditioning) that is mediated by dopaminergic circuits 
that interact with basilar structures (Lieberman 2002). If 
reward-based learning and working memory are impaired in the KE's, 
then this could explain not only their higher-level syntactic 
deficits, but also their overall lower IQ (Lieberman 2002).




Neither of these explanations of the KE's seems especially congenial 
to the linguistic nativist. For both tacitly assume that language 
learning, including syntactic learning, is not (or not entirely) 
subserved by special-purpose mechanisms. Rather, it is mediated by 
more general motor circuitry (according to the Vargha-Khadem 
hypothesis) or reward-based learning and working memory abilities 
(according to Lieberman) that are also involved in other learning 
tasks.




On the other hand, however, there is evidence that FOXP2 is
particularly implicated in vocal learning and expression. First, it is
highly expressed in songbirds that modify their innate vocal
repertoires: in canaries it is expressed seasonally, when adult birds
modify their songs (Teramitsu *et al*. 2004) and in zebra
finches, it is expressed more at the time when young birds learn their
songs (Haessler *et al*. 2004). In addition, there is evidence
that the variant of the FOXP2 gene that is present in humans has
undergone strong positive selection in the hominid line (Enard *et
al* 2002; Zhang *et al*. 2002). The protein produced by
human FOXP2 differs in just three out of its 715 constituent amino
acids from that of the mouse, and a recent analysis (Zhang *et
al*. 2003) indicates that two of these differences are unique to
the hominid lineage. According to Enard *et al* 2002, the fact
that these two differences are fixed in the human genome, whereas no
fixed substitutions occurred in the lineage of our closest relatives,
the chimpanzees, suggests that those changes were strongly selected
for in our lineage; Enard *et al*. put the date of fixation of
these changes in the human population at around 200,000 years
ago. This date accords well with at least some estimates of the
emergence of modern human language, suggesting that the vocal
capacities underwritten by FOXP2 -- and impaired in those lacking
the gene -- are after all critical to language competence.


#### 3.6.3 The grammar module and the genetics of language




At this point, two questions arise. First, is there a double 
dissociation between language capacities and general cognitive 
capacities to be found in a comparison of Williams syndrome and SLI? 
Second, what does our current knowledge of the role of FOXP2 in 
language development tell us about linguistic nativism?




As to the first question, there seems to be no double dissociation. 
First of all, WS individuals' language, while startling in contrast 
with their level of mental retardation, is not normal; indeed, as we 
have seen, it is indistinguishable on some tests from that of 
language impaired individuals. In addition, as Thomas and 
Karmiloff-Smith 2002, caution, it is not at all clear that one can 
assume, in the case of a pervasive developmental disorder like 
Williams syndrome, that apparently 'intact' competences 
are a result of normal development of the underlying neurological and
psychological structures. That is, given the known capacity of the 
brain to compensate for deficits in one area by cobbling together a 
solution in another, one cannot assume that there is a 
'language module' in WS patients which develops more or 
less normally despite other cognitive systems' being massively 
disrupted. Thomas and Karmiloff-Smith argue that the numerous 
discrepancies between WS language development and that of normal 
children suggests that this 'residual normality' 
assumption is misguided in this case, thus undermining the claim that
what is spared in WS is 'the language (or grammar) 
module.'




Moving to the other side of the dissociation, since it is hard to say
exactly what about language is disrupted in cases of SLI, it is
difficult to determine whether this disruption is specific to
language, let alone grammar. While researchers like Van der Lely and
Christian 2000, and van der Lely and Ullman 2001 argue that there is
a purely grammatical form of the deficit, which does support the
hypothesis of a grammar module, this is controversial, as we have seen
above. Certainly consideration of the KE's does not support such a
hypothesis. Their root deficit appears to concern orofacial praxis,
rather than language specifically; and in addition, their
'general intelligence,' as measured by tests of non-verbal
intelligence, while "normal," nonetheless appears to have
been affected by their neurological and/or linguistic abnormalities
-- witness their scores 18-19 points lower than those of their
relatives. It is, in other words, unclear that there is any
dissociation of language and general intelligence in this case at
all. One can conclude that as things stand now, SLI seems to be so
heterogeneous a disorder as to defy neat characterization, and that
consideration of this disorder does not support the view that there is
a language or grammar module that functions independently of other
cognitive processes.




The second question asked above was: what can be learned about the 
innate basis of language from a consideration of the KE's and FOXP2. 
In a recent article, Marcus and Fisher (2003) argue that the kinds of
results discussed above offer valuable insights into the ways that 
language is implemented in the brain and controlled (to the extent 
that it is) by the genes. However, they refrain -- rightly in my
view -- from drawing morals to the effect that FOXP2 is a 
"gene for language" or even "for 
articulation." The effects of FOXP2 are wider than this (it is 
expressed in the developing heart and lungs, in addition to the brain
-- REF) and the functions of the neural circuits in which it is 
active are as yet too poorly understood to do more than gesture at 
the ways in which FOXP2 is involved in constructing the human 
linguistic phenotype.




All the topics covered in SS3 deserve books of their own. My aim
here has been to sketch the ways in which modern understanding of the
mind reveals the inadequacy and implausibility of the claim that
humans have innate representations of UG that are responsible for
their acquisition of language. There are likely many, many processes
implicated in the attainment of linguistic competence, that many of
them are likely specialized by natural selection for linguistic tasks,
but that many of them also retain their other, and older,
functions. The linguistic nativist's theory views our acquisition of
grammatical competence as a *simple* matter -- one that
can be described at one level of explanation, and in terms of a single
kind of process. This is very unlikely to be the case. Multiple
systems and multiple processes are at work in the acquisition of
linguistic knowledge, and our understanding of language acquisition,
when it comes, is likely to involve theories of many kinds and at many
different levels, and to resemble the theory of the Chomskyan nativist
in few or no
 respects.[29]