## 1. Quine's life and work




|  |  |
| --- | --- |
| 1908  | Born, Akron, Ohio, on June 25th. |
| 1926-30  | Attended Oberlin College, Ohio; B.A, major in Mathematics with
honors reading in mathematical philosophy. |
| 1930-32  | Attended Harvard University; Ph.D. in Philosophy, dissertation
on Whitehead and Russell's *Principia Mathematica*. |
| 1932-33  | Held a Sheldon Traveling Fellowship and visited (most notably)
Vienna, Warsaw, and Prague (where Carnap was then teaching). |
| 1933-36  | A Junior Fellow in Harvard's newly-formed Society of
Fellows; worked chiefly on logic and set theory. |
| 1934  | Published *A System of Logistic*, a revised version of
his dissertation. |
| 1936-78  | Held teaching positions at Harvard, first as Faculty Instructor,
then as Associate Professor (1941) and then as Professor (1948). |
| 1940  | Published *Mathematical Logic*. |
| 1942-45  | U.S. Navy, working chiefly in Naval intelligence. |
| 1953  | Published *From a Logical Point of View*. |
| 1960  | Published *Word and Object*. |
| 1963  | Published *Set Theory and its Logic*. |
| 1966  | Published *Ways of Paradox*. |
| 1969  | Published *Ontological Relativity and Other Essays*. |
| 1974  | Published *The Roots of Reference*. |
| 1981  | Published *Theories and Things*. |
| 1990  | Published *Pursuit of Truth*. |
| 1995  | Published *From Stimulus to Science*. |
| 2000  | Died, Boston, Massachusetts, December 25th. |



(Note: for the sake of brevity, we have listed only Quine's most
notable books, including collections of essays.)


## 2. Quine's Naturalism and its Implications


### 2.1 Introduction



Quine's philosophical thought is remarkably consistent over the
course of his long working life. There are developments, of course,
but outright changes of mind are relatively rare and mostly on
relatively minor points. We can, for the most part, treat him as
having a single philosophical orientation, to which what he calls
"naturalism" is fundamental. This is not to say that his
naturalism is self-conscious and explicit from the start; it is,
rather, something that he became clearer about over the years. (For
the development of Quine's naturalism, see Verhaegh, 2018; for
the very early Quine, see Sinclair 2022.)



The term "naturalism" has been understood in various ways;
we need to see what Quine's naturalism comes to. At one point,
he describes naturalism as "the recognition that it is within
science itself, and not in some prior philosophy, that reality is to
be identified and described" (1981, 21). Two points are
important to note about the idea of "science" here. First,
it is less restrictive than it may seem. Quine certainly takes the
natural sciences, especially physics, as paradigmatic. As he says
himself, however, he uses the word "science" broadly; he
explicitly includes psychology, economics, sociology, and history (see
1995, 49). Second, Quine does not see scientific knowledge as
different in kind from our ordinary knowledge; he sees it, rather, as
the result of attempts to improve our ordinary knowledge of the world:
"Science is not a substitute for common sense but an extension
of it." (1957, 229). The scientist, he says, "is
indistinguishable from the common man in his sense of evidence, except
that the scientist is more careful." (1957, 233). We might add
that the scientist is more narrowly focused on issues of truth and
objectivity and, in the hope of contributing to these goals, clearer
and more systematic.



Many philosophers would no doubt accept that the methods and
techniques of science are the best way to find out about the world.
(With or without the points just noted about the word
"science".) The distinctiveness of Quine's
naturalism begins to emerge if we ask what justifies this naturalistic
claim: what reason do we have to believe that the methods and
techniques of science are the best way to find out about the world?
Quine would insist that this claim too must be based on natural
science. (If this is circular, he simply accepts the circularity.)
This is the revolutionary step: naturalism self-applied. There is no
foundation for Quine's naturalism: it is not based on anything
else.



The point here is that Quine denies that there is a distinctively
philosophical standpoint, which might, for example, allow
philosophical reflection to prescribe standards to science as a whole.
He holds that all of our attempts at knowledge are subject to those
standards of evidence and justification which are most explicitly
displayed, and most successfully implemented, in the natural sciences.
This applies to philosophy as well as to other branches of knowledge.
The epistemologist, therefore, reflects on science from within
science; there is no theory of knowledge distinct from science.
"Epistemology", Quine says, "...is contained in
natural science, as a chapter of psychology" (1969, 83). (For an
alternative view of the relation of philosophy to science, based on
discussion of the history of science, see Friedman, 1997.)



In Quine's view, philosophers can, therefore, do no better than
to adopt the standpoint of the best available knowledge, i.e. science,
in some suitably broad sense. We adopt what he calls "the
fundamental conceptual scheme of science and common sense"
(1960, 276). Philosophers are thus to be constrained by scientific
standards. In (1974) he puts it this way: "In our account of how
science might be acquired we do not try to justify science by some
prior and firmer philosophy, but neither are we to maintain less than
scientific standards. Evidence must regularly be sought in external
objects, out where observers can jointly observe it...."
(1974, 34f.)


### 2.2 Negative Aspects



The view sketched above has both positive and negative aspects. The
latter are better-known, and Quine is often thought of as a negative
philosopher, primarily concerned to criticize others. He casts doubt
on terms which many philosophers take for granted. He does not dismiss
such terms as meaningless, but simply as not meriting a place in
serious science, or in the objective account of the world at which
science aims. A well-known and important example is his criticism of
the idea of meaning, in the sense of the meaning of a particular
sentence or statement. Quine says: "Meaning... is a worthy
object of philosophical and scientific clarification and analysis,
and... it is ill-suited for use as an instrument of philosophical
and scientific clarification and analysis." (1981, 185). The
term is insufficiently clear, and putative explanations which employ
it are in fact unexplanatory; by engendering the illusion of
explanation they tend to impede the progress of science. So
philosophers should not rely on the term. He makes similar remarks
about "thought", "belief",
"experience", "necessity", and other terms
which many philosophers assume are legitimate and available for
philosophical use without themselves requiring explanation and
justification in other terms. (For an illustration of Quine's
attitude towards the term "meaning" as used by one such
philosopher, see his reply to Pagin in Orenstein and Kokato,
420f.)



This criticism of the scientific and philosophical use of certain
ordinary terms goes along with rejection of philosophical questions
which make essential use of those terms. For example, many
philosophers hold that there are important philosophical problems
concerning knowledge: Do we really know anything at all? What exactly
are the conditions on knowledge? (This latter question has seemed
especially pressing since Gettier, 1963.) Quine, by contrast, finds
the word "knowledge" vague, and consequently rejects it
for serious use, saying that the word is ''useful and
unobjectionable in the vernacular where we acquiesce in vagueness, but
unsuited to technical use because of lacking a precise
boundary'' (1984, 295). Accordingly, many such questions
formulated using the term may simply be dismissed, even if it remains
eminently useful for making rough sorts of claim, when we say as above
that scientific knowledge is not different in kind from our ordinary
knowledge.


### 2.3 Positive Aspects (1): Knowledge



As we have just seen, Quine's views issue in very general
criticism of much philosophy and indeed of the assumption that the
term "knowledge" marks a clear subject of inquiry. It is,
nevertheless, a mistake to think of him as primarily a critical or
negative thinker: his criticisms rely on his positive doctrine, which
in turn generates further questions. As for whether those are
genuinely *philosophical* questions, it is implicit in what has
already been said that he would not acknowledge such a category as the
'genuinely *philosophical*' if that is meant to
imply questions which are different in kind from those of science. But
certainly he accepts that some questions are sufficiently general,
abstract, and remote from observation, that they may be classified as
philosophical. At times he assimilates the questions with which he is
concerned to those which have traditionally occupied philosophers.
Epistemology--the theory of knowledge--is a clear example,
although Quine's approach to that subject is quite different
from that of many philosophers.



In some places, Quine approaches epistemology through the problem of
scepticism about the external world. But he has no room for the kind
of scepticism which asks the following kind of question: even if our
alleged knowledge, our science, is completely successful in its
predictions, how do we know that it tells us the way the world really
is? (See Alston, 1993.) Thus Quine says:



> 
> Our scientific theory can go wrong, and precisely in the familiar way:
> through failure of predicted observation. But what if... we have
> achieved a theory that is conformable to every possible observation,
> past and future? In what sense could the world then be said to deviate
> from what the theory claims? *Clearly in none*.... (1981,
> 22; emphasis added)
> 



This dismissal of one kind of scepticism is an example of
Quine's naturalism, and indicates how he understands that
idea.



There is, however, a way of understanding the sceptical question which
Quine takes seriously. Philosophers have been concerned with the gap
between what is given in experience and the knowledge that we take
ourselves to have. Quine invokes gestalt psychology and argues that
the simple sensory ideas which Berkeley and Hume had claimed were
given by the senses are not in fact given, that we see things in
three-dimensions, for example, instead of having to infer the third.
He does not, however, conclude that there is no problem at all here.
Rather, he says, "the problem was real but wrongly viewed"
(1974, 2). Epistemology, as he sees it, is here "confronting a
challenge to natural science that arises from within natural
science." (*loc. cit.*). What is the challenge? It starts
with what Quine takes to be "a finding of natural science
itself... that our information about the world comes only through
impacts on our sensory receptors" (1990a, 19). The sceptical
challenge is then: "How... could one hope to find out about
that external world from such meager traces? In short, if our science
were true, how could we know it?" (1974, 2).



Scepticism, understood in this fashion, is a challenge to
Quine's form of naturalism. It questions whether our knowledge
can be accounted for in terms which are, by Quine's standards,
purely naturalistic. Quine's response is thus to sketch an
austerely naturalistic account of how our knowledge, and the cognitive
language in which that knowledge is embodied, arises, or might arise.
This project, as he sees it, is essential to the defence of his
naturalistic world-view. (Section 4. will go into more detail about
the project.)



When Quine asks: "How... could one hope to find out about
that external world from such meager traces?" this is not a
rhetorical question. It is, rather, a serious question, to be answered
by deploying the full resources of our knowledge; it is a scientific
question. Quine recognizes that the question, thus construed, is not
exactly what earlier epistemologists had in mind, but argues that the
change is justified: "A far cry, this, from the old
epistemology. Yet it is no gratuitous change of subject matter, but an
enlightened persistence rather in the original epistemological
problem." (1974, 3).


### 2.4 Positive Aspects (2): the Nature of the World



The defence and articulation of Quine's naturalism requires
Quinean epistemology, an analogue of traditional epistemology but
carried out as a scientific enterprise. It also requires that he set
out, in outline, what is to be included in a naturalistic account of
the world; in other words, it requires an account of the world, a
least in broad outline. Among other things, this account constrains
his epistemology, since that is to be a naturalistic account of
knowledge.



In what follows, we shall sometimes speak of Quine's account of
the world as his "metaphysics", but it is metaphysics
naturalized: it is not carried out *a priori*, or by reflection
on the nature of Being *qua* Being, or anything of that
sort. (Quine himself does not much use the word
"metaphysics". He puts forward views on metaphysical
topics--such as ontology, time, and abstract objects--but
within the confines of his naturalism.)



Quine approaches his naturalistic analogue of metaphysics through the
idea of regimented theory. Regimented theory is our overall science,
the sum total of our best and most objective knowledge about the
world, reformulated in the clearest and simplest form. Quine sees this
kind of reformulating as of a piece with ordinary scientific
endeavours, but carried further than working scientists are likely to
have reason to do. He discusses the distorting effect which language
is likely to have on our view of the world and comments:



> 
> To some degree...the scientist can enhance objectivity and
> diminish the interference of language, by his very choice of language.
> And we [meaning we philosophers, we scientists at the abstract and
> philosophical end of the spectrum], concerned to distill the essence
> of scientific discourse, can profitably purify the language of science
> beyond what might reasonably be urged upon the practicing scientist.
> (1957, 235)
> 



Regimented theory is, of course, an idealization. It is not a complete
and finished object, available for us to examine. Quine's
reflections on it might be considered as something like a
thought-experiment: if we were to set about assembling our total
theory of the world and recasting it in the best form, what would it
look like? Since the enterprise is not in fact going to be carried out
all the way we are not going to get a detailed answer. But on some
important general issues, Quine holds, we can get answers. In
particular, he argues that the framework of regimented theory is
first-order logic with identity (and so that theory is extensional);
that the variables of this theory range only over physical objects and
sets; and that the predicates of the theory, the only non-logical
vocabulary, are physicalistic, in his somewhat complicated sense. (See
section 5, below.) Although this is not traditional *a priori*
metaphysics, we should not underestimate the ambition of the project.
He says of his regimented theory that "all traits of reality
worthy of the name can be set down in an idiom of this austere form if
in any idiom" (1960, 228) and speaks of "limning the true
and ultimate structure of reality" (1960, 221). The claim that
the variables of regimented theory range only over physical objects
and sets is, as far as he is concerned, the claim that only physical
objects and sets really exist.


## 3. The Analytic-Synthetic Distinction and the Argument Against Logical Empiricism



The philosophers who most influenced Quine were the Logical
Empiricists (also known as Logical Positivists), especially Rudolf
Carnap. The distinction between analytic truths and synthetic truths
plays a crucial role in their philosophy. Analytic truths might be
characterized as those true solely in virtue of the meanings of the
words they contain, or of the rules of the language, or something of
the sort. Synthetic truths, by contrast, state matters of
extra-linguistic fact, and are known by experience. The Logical
Empiricists accounted for truths which do not seem to be answerable to
experience, most obviously the truths of logic and mathematics, by
saying that they are analytic. This position was very widely held by
the 1940s. Quine, however, famously casts doubt on analytic-synthetic
distinction, and rejects the use made of it by the Logical Empiricists
and other philosophers from the 1930s on. (Notable among the others is
C. I. Lewis, first a teacher and then a colleague of Quine; his
influence on Quine has perhaps been underestimated. See Baldwin 2013,
Ben-Menahem 2016, and Sinclair 2016.)



The issues here are complex, and the argument takes many twists and
turns. The aim of this section is to give an account of Quine's
mature view, and of the strongest arguments that he has for it.


### 3.1 Carnap's Principle of Tolerance and Quine's Objections



Carnap holds that the role of philosophy is to analyze and clarify the
language of science, and to formulate and recommend alternative
languages. After 1932, he holds that there are languages which differ
in expressive power, not merely as notational variants. The difference
between intuitionistic logic and classical logic is an important
example here, as is the difference between the language of Newtonian
mechanics and the language of relativistic mechanics. (Earlier, he
says, he had 'overlooked the fact that there is a multiplicity
of possible languages', Carnap 1934, 245; cf. also 322 of the
same work.) Within a given language, there may be only one correct
theory on a given subject. But the choice of a language is in that
respect unlike the choice of a theory. In deciding which theory is
correct, we will appeal to observations but also to the rules of the
language; no such appeal is possible when we are choosing a language,
for in this case it is the rules themselves that we are choosing. So
Carnap holds that there is no one *correct* language. This idea
has become known as the Principle of Tolerance; from the 1930s on, it
is fundamental to Carnap's view of what philosophy is and how it
differs from science. (That there is such a difference is a point
which Carnap never questions.) Because there is no one correct
language, it is no part of the philosopher's job to prescribe
this or that language, merely to analyze, to clarify, and to suggest
alternatives.



The Principle of Tolerance requires the analytic-synthetic
distinction. It requires that we can, in all cases, distinguish
between theoretical changes which involve a change of meaning, and
hence, strictly speaking, a change of language, and those which do
not. The former kind of change involves analytic sentences, and is a
matter for Tolerance; the latter involves only synthetic sentences,
and Tolerance does not apply. The use of the Principle of Tolerance
thus presupposes a clear distinction between the analytic sentences of
the language and its synthetic sentences.



At least as Quine sees the matter, the use of the Principle of
Tolerance puts analytic sentences on an entirely different
epistemological footing from synthetic sentences. Synthetic sentences
are answerable to evidence; analytic sentences are a matter of the
choice of language, which does not require theoretical justification.
Quine, however, rejects the idea that there is such an epistemological
difference. Even if we can distinguish the analytic sentences from the
synthetic sentences, we may still have reasons to reject an analytic
sentence. And those reasons may be of the same kind that lead us to
reject synthetic sentences. This point is hard to see if one focuses
on examples such as "All bachelors are unmarried". The
matter is otherwise if one considers examples such as "Force
equals mass times acceleration". (See Putnam, 1962.) A change of
mind about an analytic sentence would be a change in the language.
Still, we might have reasons to make such a change, reasons that are
of the same sort that lead us to make revisions to synthetic
sentences. In that case, we have no more reason to apply Tolerance in
the one kind of case than in the other.



This is the view that Quine argues for. On the one hand, he emphasizes
the point (which Carnap largely accepts) that choice of language is
not theoretically neutral: some choices will make for a better theory
than others. On the other hand, he argues that 'pragmatic'
factors, such as simplicity, which Carnap had accepted as playing a
role in choice of language, also play a role in the choice of a theory
within a language. Hence, he claims, the two sorts of choice are on
the same epistemological footing, and the Principle of Tolerance is
unjustified.



Quine's argument for this position relies on *holism*.
This is the claim that most of our sentences do not have implications
for experience when they are taken one-by-one, each in isolation from
the others. What has experiential implication is, in most cases, not
an individual sentence but a larger chunk of theory. Holism is not a
very controversial doctrine. (Carnap accepts it; see Carnap, 1934,
318.) Quine claims that holism shows that most of our sentences are
not justified by the relation of the individual sentence, considered
in isolation, to experience. Almost always, what matters is the
relation to experience of some larger chunk of theory (in principle,
although perhaps never in practice, of the theory as a whole). This
means that in principle the correctness of a given claim is almost
never settled simply by looking at the empirical evidence for that
claim alone. Other factors will play a role, in particular the way in
which accepting the given claim would contribute to the efficacy and
simplicity of the theory as a whole. But these are precisely the
'pragmatic factors' which Carnap thought played a role in
the choice of language. In arguing that such factors play a role
throughout our knowledge, Quine accepts 'a more thorough
pragmatism' (1951, 46) which puts Carnap's external
changes on the same epistemological footing as his internal changes.
(Quine's early account of these matters is extremely sketchy.
For elaboration, see Quine 1991 and 1996; for criticism of the sketchy
account, see Sober 2000.)


### 3.2 Quine's Alternative



If logic, mathematics, and other putatively *a priori* parts of
our knowledge, are not to be explained by analyticity, how are they to
be accounted for? Holism, which is central to Quine's argument
against Carnap, also provides him with an alternative position. It
seems as if logic and mathematics have a special status because they
are independent of experience. They appear to be necessary and not
susceptible of refutation by what future experience brings; they
appear to be *a priori* because we know them independent of
experience. Carnap sought to explain these appearances by appealing to
the idea that accepting an analytic sentence of a given language goes
with speaking that language, and to the Principle of Tolerance. Since
choice of language is not justified by experience, the truth of the
analytic sentences of a given language is not answerable to
experience.



How is Quine to explain the apparent necessity and *a priori*
status of some truths without appeal to the Principle of Tolerance?
Quine's holism is the view that almost none of our knowledge is
*directly* answerable to experience. (The exceptions are what
he calls 'observation sentences'; see 4.2, below.) In
almost all cases the relation is indirect: a given sentence is only
answerable to experience if a body of theory is presupposed. (When we
say that a given observation confirms or refutes a given theoretical
claim, we are tacitly presupposing other theoretical knowledge.) This
is most easily seen if we consider a highly theoretical sentence, but
in Quine's view it holds, of almost all our sentences. The
reason to accept a sentence is its contribution to the success of
theory as a whole as an efficient and simple method of dealing with
and predicting experience; in principle, this means the success of our
theory as a whole, the whole body of sentences that we accept, in
dealing with experience as a whole.



For many of our sentences, this strong statement of holism holds only
in principle. In practice, we may have a good idea what experiences
would lead us to change our minds about a given sentence, and what
further changes in theory would follow. Elementary arithmetic (to take
that as an example) is different because it is involved in almost
every part of systematic knowledge. (In Quine's well-known
metaphor, it stands near the centre of the 'web of
belief'.) Abandoning it would mean abandoning our whole system
of knowledge, and replacing it with an alternative which we have not
even begun to envisage. Nothing in principle rules out the possibility
that the course of experience will be such that our present system of
knowledge becomes wholly useless, and that in constructing a new one
we find that arithmetic is of no use. But this is a purely abstract
possibility, certainly not something we can imagine in any detail. So
the idea that we might reject arithmetic is likewise unimaginable;
hence the truths of arithmetic appear to be necessary.



For similar reasons, arithmetic appears to be *a priori*. No
particular experience confirms '2 + 2 = 4'. (Quine is not
advancing what Frege derided as a 'gingerbread and pebble'
account of arithmetic (Frege 1884, vii), in which the sentence is
justified by our observations of cookies or stones.) Arithmetic is
independent of any particular experience, or any easily specifiable
portion of experience; hence it appears as *a priori*. On
Quine's account, it rests on our experience as a whole, and the
fact that the theory which best accounts for that experience makes
essential use of arithmetic.


### 3.3 Meaning and Quinean Analyticity



As we have just seen, even sentences which we cannot imagine rejecting
might, in principle, be rejected. As Quine says: 'no statement
is immune to revision' (1951, 43; see Ebbs 2017, Ch. 8). This
claim of Quine's has attracted a good deal of attention, and is
sometimes thought to be shocking or even paradoxical. In the context
of his debate with Carnap, however, it is not, by itself, at all
surprising. For Carnap too, any sentence can be revised; he would
insist, however, that in the case of some sentences, the analytic
ones, a revision involves a change of language, and thus of the
meaning of the words used in the sentence. So the idea of meaning, and
sameness of meaning, occupies a crucial role in the debate over
analyticity.



Quine's initial arguments against the analytic-synthetic
distinction seek to cast doubt on the idea that there is a notion of
meaning which is clear enough to use in defining a notion of
analyticity. He explores various proposals and finds them wanting.
(See especially Quine 1951.) Here too a crucial role is played by
holism. One apparently clear conception of meaning is that the meaning
of a sentence is given by the experiences which would confirm it;
holism, however, implies that the idea of confirmation does not apply
to individual sentences, considered in isolation from the theories of
which they are parts. (For criticism see Fodor and Lepore 1992; for a
counter to Fodor and Lepore see Heal 1994; for later Quine on holism
see his 1991.)



Quine's scepticism about the idea of meaning is much criticized.
We will mention two criticisms. First, what standards of clarity is he
employing, when he says that the notion of analyticity is
insufficiently clear? The answer, not explicit in Quine (1951), is
that the standards are those indicated by our discussion in the
previous section; Quine is asking for an explanation which is
acceptable by his naturalistic standards (see Lugg 2012). Such an
explanation would not presuppose an idea of meaning, and would use
such ideas as definition or convention only in ways which are
justified by the literal sense of those terms. Second, some responses
to Quine's position here argue that it has obviously absurd
consequences, such as that meaningful discourse would be impossible or
that we could not understand our language. (See, for example, Grice
and Strawson, 1956.) But Quine's scepticism about
*meanings* does not lead to any scepticism about
*meaningfulness*. If we think of meaningfulness as a matter of
*having a meaning* then we may think that our words cannot be
meaningful unless there are meanings. But such a way of thinking is,
Quine claims, quite misleading. In Quine 1953, he offers a rough and
ready behavioural account of meaningfulness; it is clear from the way
the account proceeds that the success of something along those lines
would be of no help at all in defining synonymy or analyticity.



We said above that Quine seeks 'to cast doubt' on the idea
of meaning, and on the use of that idea to explain the distinction
between those changes of doctrine which involve a change of meaning
and those which do not, and thus also to explain analyticity. One
might read Quine 1951 and get the impression that he is not merely
casting doubt but wholly rejecting these ideas. In later works,
however, he himself suggests a definition of analyticity. A sentence
is analytic for a given native speaker 'if he learned the truth
of the sentence by learning to use one or more of its words'
(Quine 1991, 270; see also Quine 1974, 78-80). It is analytic
without qualification if it is analytic for all native speakers. By
this criterion, some obvious truths, such as 'Bachelors are
unmarried', will presumably count as analytic. If we think of
the set of analytic sentences as closed under logical consequence, as
Quine suggests, then, he says, all first-order logical truths
'would then perhaps qualify as analytic' (Quine 1991,
270). Along with this, he comes to accept that certain revisions of
belief do involve a change of meaning, presumably in a sufficiently
clear sense of meaning (Quine 1991, 270).



Now it might seem as if Quine completely withdraws his earlier
criticism of the analytic-synthetic distinction and thus, presumably,
of Logical Empiricism as a whole. But in fact this is not so. One
consideration here is the scope of Quinean analyticity. The idea will
perhaps (as Quine says) include first-order logic, but it will not
include mathematics; on this count alone, it is clear that it will not
do what Carnap requires of the idea of analyticity. An even more
important consideration is that Quine's version of the
analytic-synthetic distinction is not an epistemological distinction.
Some changes of doctrine involve changes of meaning, others do not. In
Quine's view, however, this does not mean that the two sorts of
change must have different epistemological bases. To the contrary: as
we saw in 3.1, Quine rejects the Principle of Tolerance and, with it,
the idea that a change of language takes place on a different kind of
epistemological basis from a change of theory within a language. His
acceptance of a limited conception of analyticity does not change this
picture. As he says: "I recognize the notion of analyticity in
its obvious and useful but *epistemologically insignificant*
applications" (1991, 271; emphasis added).



On the interpretation advanced here, Quine's rejection of the
Principle of Tolerance is the deepest aspect of his disagreement with
Carnap. Quine sees all our cognitive endeavours, whether they involve
formulating a new language or making a small-scale theoretical change,
as having the same very general aim of enabling us to deal with the
world better; all such endeavours have the same very general kind of
justification, namely, as contributing to that end. In this picture,
there is no basis for Carnap's insistence that philosophy is in
principle different from science. Philosophy, as Quine sees it, has no
special vantage point, no special method, no special access to truth.
Here we have the crucial idea of Quine's naturalism, discussed
in the previous section.


## 4. Quinean Epistemology


### 4.1 The Epistemological Project



As we saw in section 2, Quine takes the fundamental epistemological
problem to be that of showing how we come to have knowledge of the
world. He seeks an account which is naturalistic in his austere sense,
and thus starts with the idea that we know about the world only from
impacts of various forms of energy on our sensory nerves (see 2.3,
above). How do we get from such impacts to something recognizable as
knowledge of the world? In the words of the title of Quine's
last monograph: how do we get from stimulus to science?



This question is central for Quine's scientific naturalism in
general. An answer would show that that world-view can accommodate an
account of human knowledge. If no answer is available, that world-view
is cast in doubt. For these purposes it is perhaps enough if Quine can
sketch an account, compatible with his naturalistic view, of how we
*might* acquire the knowledge which we take ourselves to have,
whether or not it is correct in detail. (See Quine 1990c, 291.)



Quine treats knowledge as embodied in language. Apart from other
considerations, language-use is observable and thus subject to
scientific inquiry. Quine's concern with how we might acquire
knowledge thus takes the form of a concern with how we might acquire
cognitive language. But his interest here is in epistemology, rather
than in language for its own sake: "I am interested in the flow
of evidence from the triggering of the senses to the pronouncements of
science.... It is these epistemological concerns, and not my
incidental interest in linguistics, that motivate my
speculations." (1990b, 3).



Much of Quine's work in epistemology is thus a discussion of how
a child might acquire cognitive language. This genetic project may
seem to be a long way from the traditional concerns of epistemology.
Quine claims, however, that the project in fact affords us the best
obtainable insight into the nature of the evidence for our theories,
and into the relation between theory and evidence: "the
evidential relation is virtually enacted, it would seem, in the
learning." (1975b, 74-75).


### 4.2 Observation Sentences



Central to Quine's naturalistic account of knowledge is the idea
that all our knowledge is in some way based upon stimulations of our
sensory nerves. For much of our knowledge, the relation is quite
indirect. (This is one way of expressing holism; see 3.1, above.) Most
sentences are not accepted because of a direct relation between the
given sentence and stimulations of nerve endings; the connection goes
via other sentences, and may be quite indirect and remote. But then
there must presumably be some sentences which are directly related to
stimulations. This is the role that observation sentences play in
Quine's thought. Acts of uttering such sentences, or of
assenting to them when they are uttered by others, are shared
responses to stimulation. (We shall enter some qualifications at the
end of this sub-section.)



Observation sentences are the starting point for our acquisition of
knowledge, the child's entry into cognitive language. They are
also the sentences which are evidentially basic. What fits them to
play both roles is that they are (largely) independent of other parts
of our language. Hence they can (largely) be mastered by a child
otherwise without linguistic competence, and known without
presupposing other parts of our theory. (The reason for the
qualification will become apparent at the end of this
sub-section.)



Many philosophers are content to take for granted the idea of an
evidentially basic sentence. Quine, however, cannot take that
attitude; he needs to show how we get "from stimulus to
science". The first step is to show that we can give a purely
naturalistic account of how some linguistic utterances can be directly
tied to the occurrence of stimulations of the sensory nerves---an
account of observation sentences, more or less. Quine expends enormous
labour on this point.



Quine considers acts of assenting to sentences (or dissenting; but we
shall mostly leave that as understood). He focuses, in particular, on
our *dispositions* to assent to sentences. (We will briefly
consider the idea of a disposition in the next section.) To be an
observation sentence, a sentence must fulfill two criteria, one
individualistic and one social. The individualistic criterion is that
a sentence is an observation sentence for a given person if he or she
is disposed to assent to it when, and only when, he or she is
undergoing appropriate sensory stimulations, regardless of her
internal state (e.g. the ancillary information which he or she
possesses). "It's warm in here" presumably satisfies
this criterion; my willingness to assent to it perhaps depends only on
which of my sensory nerves are stimulated at the given moment.
"There's milk in the refrigerator" presumably does
not; unless I am actually looking into the refrigerator at the time,
my willingness to assent to it depends not on what I am experiencing
at the time but on my internal state, what I remember. The social
criterion is that the individualistic criterion should hold across the
linguistic community as a whole. To specify this more precisely is
tricky, and we shall postpone the matter for a few paragraphs.



Even the individualistic criterion raises considerable complications
and difficulties. We speak of a disposition to assent (or dissent) in
response to a pattern of stimulation but this is not quite accurate.
Such a pattern, a complete list of which sensory nerves are firing,
and in which order, will hardly ever repeat itself. So what we need
is, rather, the idea of a correlation of a response with a
*type* of stimulation
 pattern.[1]
 But the relevant idea of a type here is complicated. The physical
resemblance of two stimulation patterns, what Quine calls
*receptual* *similarity*, is not enough to make them
constitute events of the same type, in the relevant sense; two such
patterns may resemble each other very closely yet lead to quite
different responses. (Two occasions on which I am driving a car may be
almost identical in terms of my stimulation patterns, except that on
one occasion I see a red light and on the other I see a green light.
As far as my response goes, that small difference outweighs all the
similarities.) What is wanted is a more complex notion which Quine
calls *perceptual similarity*. Very roughly, two stimulation
patterns count as similar (for an animal, at a time) if they tend to
lead to the same
 response.[2]



With the account of perceptual similarity in place, we can say what it
is for a sentence to be observational for me: if I am disposed to
assent to it on one occasion on which I have a certain neural intake,
then I will also be disposed to assent to it on any other occasion on
which I have neural intake which is (sufficiently) perceptually
similar for me at that time.



It is worth emphasizing the fact that the definition of the key notion
of perceptual similarity is behavioural. It avoids any idea of
experience, of awareness, of what strikes the person (or other animal)
as more similar to what. It is simply a matter of responses, and thus
of behaviour. (Assent is also treated as behavior, as sound-making
propensities; see 1975c pp. 87-88). This is in accord with
Quine's insistence on what he takes to be scientific standards
of clarity and rigour. One consequence of it is that the notion cannot
be invoked to *explain* behaviour. Quine is under no illusions
on this score. (See 1975c, 87, where the point is explicit.) The
behavioural account does not *explain* our understanding of
observation sentences; explanation, if possible at all, comes at the
neuro-physiological level. What the behavioural account does is to
make clear exactly what behaviour constitutes that understanding and,
hence, what the neuro-physiological account would have to explain. (It
also shows that there is indeed something to be explained.)



So far we have only an account of what it is for a sentence to be an
observation sentence for a particular person. But our language is
shared, as it must be if it is to enable us to communicate with one
another. So we need to generalize the criterion across the linguistic
community. One might at first think that the social criterion would
be: if one person is disposed to assent to the sentence on any
occasion on which he or she has a certain neural intake, then any
other person having the same neural intake will also be disposed to
assent to it. Quine gives essentially this account in (1960). As he
quickly comes to see, however, it is not tenable, for it assumes that
we can make sense of the idea of "same neural intake"
between different people. But different people have different sensory
nerves (and there is no reason to suppose that one person's
sensory nerves are homologous to those of others; see Quine 1969,
chapter 6).



Quine returned to this problem on and off over the next thirty-five
years. His eventual solution is that a sentence only counts as an
observation sentence if an occasion which leads to my having neural
intake which disposes me to assent to it also leads to your having
neural intake which disposes you to assent to it. Here there is no
cross-person identification of neural intake or cross-person standards
of perceptual similarity. On this account, however, there can only be
observation sentences if our standards of perceptual similarity line
up in the right way. Two occasions which produce in me neural intakes
which are perceptually similar by my standards must also (often
enough) produce in you neural intakes which are perceptually similar
by your standards. Quine is happy enough with this assumption of
mutual attunement and suggests that it can be explained along
evolutionary lines (see 1996, 160f., and for the whole story, Kemp
2022, 805-810).



We have been explaining the idea of our having shared responses to
stimulation. For the most part, Quine assumes that assent to an
observation sentence simply is such a response. This assumption,
however, cannot be quite correct. It may look for all the world as if
there were a rabbit in front of me, even though there is not. If I
have no reason to be suspicious I will be disposed to assent to
"Rabbit?"; if I know about the deception, however, I will
not be. So my disposition to assent does not, after all, depend solely
on my sensory stimulations at the time. It depends also on my internal
state, whether I know that in this case the rabbit-like appearance is
misleading. The difficulty arises because "There's a
rabbit" is corrigible, a feature which, on most accounts, it
shares with just about every sentence other than those about the
speaker's current experience. If a sentence is corrigible then
there will be circumstances in which it is false, even though those
circumstances produce stimulation patterns which would generally lead
observers to assent to it. But then some observers may know that the
circumstances are of this deceptive kind and not be disposed to
assent, while others have no such knowledge and are disposed to
assent. The moral of this is that assent, even to observation
sentences, is not a mere response to stimulation; the
responder's internal state (having ancillary knowledge, or not)
may also play a role.



Quine does not seem to have fully appreciated this point, though some
of his later discussions come close to doing so (see, in particular,
Quine 1996). It is not fatal to his general account; it complicates
the story rather than requiring a radical change. There may be no
sentences--at least none that satisfy the social criterion for
observationality--which can be wholly mastered simply by
acquiring appropriate dispositions to assent and dissent in response
to current stimulations. For some sentences, however, acquiring such
dispositions comes close to mastering their use, because those
sentences are *almost always* true in those cases where
observers receive sensory stimulations which dispose them to assent.
(Clearly this will be a matter of degree.) So the acquisition of the
relevant dispositions, and partial mastery of the sentence, can be
used as a basis on which the child can learn more of the language, and
more about the world. This further learning in turn allows the child
to modify her or his original disposition to assent and dissent merely
in response to current stimulation.


### 4.3 More Complex Forms of Cognitive Language



Quine's treatment of more sophisticated parts of language is
notably sketchier and more speculative than his detailed discussion of
observation sentences. In part this may be because he holds that it is
most important to understand the very first step into cognitive
language, how such language is possible at all. It may also be that
the difficulty of getting a satisfactory account of observation
sentences impeded him.



Beyond these points, however, there is, from a Quinean perspective, a
limit to how detailed an account we should expect to have of the
acquisition of sophisticated cognitive language. Mastery of an
observation sentence corresponds (more or less) to a relatively
straightforward disposition: to assent when receiving a stimulation
pattern within a certain range. For most sentences, however, this is
not the case. What disposition must one have acquired in order to
count as understanding a sentence such as "The economy is in
recession"? No doubt the disposition to assent in response to
evidence is required, but what counts as evidence is almost
unmanageably diffuse. In such a case, the links between sensory
stimulation (such as that induced by the sight of words in a
newspaper) and assent are "multifarious [and] not easily
reconstructed even in conjecture" (1960, 11). A relatively
clear-cut account, of the sort that Quine gives of observation
sentences, is simply not available.



So Quine does not offer any sort of detailed account of the
acquisition cognitive language beyond the observation sentences. (For
comparison of Quine's approach here with the very different
approach of Chomsky, see Smith 2014.) Instead, he considers stages on
the way, forms of language which one might suppose could be easily
acquired by a child who has mastered observation sentences and which
might provide steps leading to yet more advanced language.



One such step, which is emphasized in Quine's later work, is the
mastery of what he calls observation categoricals (1981 p. 28) These
are sentences of the form "Whenever X [happens], Y
[happens]", where the schematic letters are to be replaced by
observation sentences. (E.g. "Whenever there's smoke,
there's fire.") It is plausible to suppose that a child
who has learnt the observation sentences can come by a mastery of the
relevant observation categorical. Observation sentences are what Quine
calls occasion sentences, true on some occasions and false on others,
whereas observation categoricals are eternal sentences, true or false
once for all. Quine suggests that we can think of observation
categoricals as a plausible first step towards a general mastery of
eternal sentences, which make up our serious theoretical
knowledge.



Another step of the same kind is what Quine calls eternal
predications, subject-predicate sentences true or false once for all,
such as "Fido is a dog". Assuming the child has learnt
each term as an observation sentence, the sight of the dog will
dispose him to assent to each. Quine speculates that the sound of the
word "Fido" may have something of the same effect as the
sight of the beast, inclining our learner to assent to
"Dog" and thus to "Fido is a dog". It is
notable that there is a sort of use-mention confusion operating here,
if Quine's suggestion is correct. Language is learnt by
confusion and "short leaps of analogy" rather than by
"continuous derivation" (1975b, 77f.); indeed a holistic
language cannot be learnt without such leaps.



A further advance, in Quine's view, takes place when the child
comes to use similar sentences but with two general terms, such as
"Dogs are animals". Such a sentence, Quine remarks is
''really a universal categorical, 'Every a is
a b'.'' (1974, 66). This kind of sentence, can
be represented using pronouns ("If something is a dog then it is
an animal") or, more or less equivalently, using the logical
device of quantifiers and variables. Such sentences have a particular
importance for Quine in connection with the idea of reference. Merely
to be able to use a name, to be able to name Fido upon seeing him, for
example, is not yet to refer; one might simply be using the term as a
response to the sight of the dog, hence as an observation sentence.
Reference, as Quine sees the matter, requires the capacity to
reidentify the object over time and changing circumstances: if a dog
is barking then it--that very same dog--is hungry; hence the
importance of pronouns.


### 4.4 Other aspects of epistemology



Quine also has things to say on more familiar epistemological themes.
In some cases he indicates how they can be integrated into his
approach; thus he suggests that we can (albeit unrealistically)
schematize the testing of a scientific theory by thinking of ourselves
as deriving observation categoricals which can then be directly tested
against observation sentences. In other cases he is content to adopt
more or less unchanged the account given by earlier authors, as in his
list of the virtues of a theory (see 1990a, 20). Our account above has
stressed the most novel parts of his epistemology.



One issue left unaddressed above is the question whether Quine's
naturalized version of epistemology is normative. Some commentators
have claimed that it is not, and that this is a serious defect (see
Kim, 1988). Others claim that naturalized epistemology is normative
(see Gregory, 2008). Quine himself has weighed in, saying that critics
'are wrong in protesting that the normative element...goes
by the board' (Quine 1990a, 19). He cites the 'finding of
natural science...that our information about the world comes only
through impacts on our sensory receptors' (Quine 1990a, 19) as
being normative, 'warning us against telepaths and
soothsayers' (Quine 1990a, 19). More generally, naturalized
epistemology is concerned with 'the whole strategy of rational
conjecture in the framing of scientific hypotheses' (Quine
1990a, 20).



Naturalized epistemology is thus certainly normative in this sense: it
tells us that in drawing up scientific theories we *should*
rely on the evidence of the senses rather than on soothsayers; that we
*should* aim at simple theories, and so on. In telling us these
things, however, it relies on what we already know: it deploys some
parts of our science to guide attempts in other areas. It does not
take a normative attitude towards science as a whole, criticizing or
justifying it by wholly external, non-scientific standards. That would
require a wholly extra-scientific position, an idea which Quine
derogates as 'First Philosophy' (e.g. Quine 1981, 67). The
rejection of any such idea is one way of phrasing the naturalism he
advocates.


## 5. Metaphysics Naturalized



Quine takes seriously the idea that "it is within science
itself, and not in some prior philosophy, that reality is to be
identified and described" (1981, 21). It follows from this idea,
as he construes it, that our best scientific theory of the world tells
us as much as we know about reality. (Our best theory at given time
tells us as much as we know at that time; no doubt our views will
progress.) So setting out the broad outlines of that theory is the
Quinean version or analogue of metaphysics, though he does not much
use the word. This subject interacts with that of the last section:
Quine's account of the world both lays down the constraints
within which an account of knowledge must proceed, and is, in outline,
the knowledge that must be accounted for.


### 5.1 Method: Regimented Theory



How does Quine think we should establish the sort of claims that we
are calling "metaphysical"? Some points are familiar from
our discussion in section 2. First, we do not resort to any special
kind of philosophical insight. Second, what matters is ordinary
knowledge as refined and improved upon: science. Third, we rely upon
the idea of regimented theory, science formulated in a language that
is clarified and simplified "beyond what might reasonably be
urged upon the practicing scientist" (1957, 235; see 2.4,
above). We rely upon ordinary usage where no better is to hand, but
accept changes that are improvements (see 1960, 3). A further point is
that in striving for the clarity and simplicity of our theory we must
consider the whole theory; local gains may be offset by global losses.
It is thus to overall regimented theory that we look when we are
"limning the true and ultimate structure of reality"
(1960, 221).



What is Quine's justification for relying on the idea of
regimented theory, rather than on our ordinary conceptual scheme? (Cf.
Strawson, 1959, Introduction.) One part of the answer is that just as
science is in the same line of business as ordinary knowledge, but
does it better, so regimented language is in the same business as
ordinary language, but does it better. Regimentation, that is to say,
is not the imposition of a wholly foreign language; it is the adoption
of a language that maximizes scientific virtues already partially
present in ordinary speech--logical structure, reference, the
ready amenability to algorithmic methods. But another part of the
answer is the idea that "our ordinary conceptual scheme"
does not pick out anything definite enough to answer metaphysical
questions. Thus Quine says: "...a fenced ontology is just
not implicit in ordinary language.... Ontological concern is not
a correction of a lay thought and practice; it is foreign to the lay
culture, though an outgrowth of it." (1981, 9).



Regimentation, in Quine's view, involves paraphrase into logical
notation. Such paraphrase greatly clarifies and simplifies our theory.
Inferences which are a matter of logic will be revealed as such; where
additional assumptions are required it will be explicit just what is
needed. The logic which Quine takes as the structure of regimented
theory is classical (bivalent) first-order logic with identity.
Bivalence is justified on the grounds of simplicity. It is not that we
have some independent insight into the nature of the world which shows
us that every sentence of regimented theory is either true or false.
It is, rather, that the simplicity that we gain from making this
assumption, justifies our using a bivalent language; the metaphysical
claim follows along. (This reversal of direction should remind us of
Carnap. The difference is that Quine does not accept the Principle of
Tolerance; see section 3, above.)



Quine's choice of first-order logic, rather than second-order
logic, has been more controversial than his adoption of bivalence. One
reason he gives for the decision is that every formalization of
second-order logic (unlike first-order logic) is incomplete, relative
to the standard semantics. A further reason is that one purpose of the
canonical framework is to enable us to assess the ontology of a
theory. From this point of view it is an advantage that first-order
logic has no ontological presuppositions of its own. (By adopting that
logic we do commit ourselves to there being some object or other, but
not to the existence of any particular entity.) Here again there is a
clear contrast with second-order logic, which does have ontological
presuppositions. Exactly what those presuppositions are is unclear,
and has been debated; for Quine, this unclarity is a further reason to
avoid the subject entirely.



Paraphrasing a theory into classical logic imposes extensionality on
it: a predicate may be replaced by a co-extensive predicate without
change of truth-value of the containing sentence; likewise an embedded
sentence by a sentence of the same
 truth-value.[3]
 Extensionality imposes quite severe restrictions. It requires, for
example, that attributions of belief, and other propositional
attitudes, be regimented into a form quite different from that which
they may appear to have. (For this reason, the commitment to
extensionality is quite controversial; see Follesdal 1986 and
Kaplan 1968, 1986.) So one might suppose that Quine accepts
extensionality reluctantly, as the price to be paid for the advantages
of the use of logic in regimenting theory. Such is not his attitude,
however. To the contrary, he thinks of the clarity that extensionality
brings as a great advantage, and of theories that lack it as not fully
comprehensible: "I find extensionality necessary, indeed, though
not sufficient, for my full understanding of a theory." (1995,
90f.)


### 5.2 Metaphysical Claims



Quine's regimented theory, then, is the sum total of our
knowledge, the best that we have, reformulated so as to fit into the
framework of first-order logic. The extra-logical vocabulary consists
only of predicates. All metaphysical questions can thus be boiled down
to two: What objects do the variables range over? and: What sorts of
primitive predicates are to be admitted?



To the first of these questions Quine offers a straightforward answer:
his ontology consists of physical objects and sets. We will say a
little more about each. He counts as a physical object the matter
occupying any portion of space-time, however scattered the portion and
however miscellaneous the occupants; such an object need not be what
he calls a "body", such as a person or a tree or a
building (see 1981, 13). He briefly entertains the idea that we could
manage without postulating matter at all, simply using sets of
space-time points, where these are understood as sets of quadruples of
real numbers, relative to some co-ordinate system--that is, an
ontology of abstract objects only. He seems to see no knock-down
argument against this but abandons it, perhaps because the gain is too
small to justify the magnitude of the departure from our ordinary
views. That he is willing to consider such a view, and take it
seriously, shows something about his general attitude.



Besides physical objects, Quine's ontology includes sets. Our
ordinary (unregimented) scientific theories require mathematical
entities (numbers, functions, and so on). Set-theory enables us to
define all those mathematical entities, and many non-mathematical
entities, in clear and economical fashion; hence regimented theory
admits sets. Quine is often said to put forward an
"indispensability argument" (sometimes known as "the
Quine-Putnam indispensability argument") for the existence of
mathematical entities. (And thus, it might be said, for Platonism,
though that is not a term that Quine favors.) The argument has been
well summed-up like this: "the indispensability of mathematics
to empirical science gives us good reason to believe in the existence
of mathematical entities" (Quine 1976, 1991; see also the
introduction to the entry on
 indispensability arguments in the philosophy of mathematics).
 Taken very narrowly, it is correct to say that Quine endorses this
argument. Our ordinary theories employ mathematical entities, and so
regimented theory must give us some way of achieving the same effect;
admitting sets into our ontology is Quine's preferred method.
But ascribing that argument to Quine may be misleading if doing so is
taken to imply that he holds that there is some special problem about
the ontological status of sets, or mathematical entities, or abstract
objects in general, and that he employs the indispensability argument
to solve that problem. For the mature Quine, there is no more of a
problem with realism about abstract entities than there is with
realism about concrete objects; indeed the distinction between the
abstract and the concrete plays no significant role in his mature
thought (see 1960, 233). All questions of existence and reality
are to be settled in the same way: entities exist if and only if the
quantifiers of regimented theory range over them. 



Quine does not accept the existence of any abstract objects apart from
sets. His ontology thus excludes other alleged abstracta, such as
properties, propositions (as distinct from sentences), and merely
possible entities. The chief reason for his denial of the existence of
such alleged entities is that he finds their identity-criteria
unclear; he holds, quite generally, that we should not postulate
entities without having clear identity-criteria for them. (This is the
view that he sums up in the slogan "no entity without
identity"; see (1969, 23) and elsewhere.) Doing so would
threaten the clarity and definiteness which the notion of identity
brings to theory; local gains from postulating, say, propositions are
not worth this global loss. (For a contrary view about properties, see
Armstrong 1980.)



Regimented theory also has no place for mental entities, most
obviously minds, if those are taken to be distinct from physical
entities. The qualification is important. Many mental entities can be
admitted as special cases of physical objects. Thus my act of thinking
about Fermat's Last Theorem at a particular time can simply be
identified with my body during that period of time (see 1995, 87f.).
The things that we might want to say about my act of thinking (that it
was inspired, or stupid, or what have you) can simply be reconstrued
as predicates true or false of physical objects. This is the view
sometimes known as anomalous monism or as token-token identity theory,
as distinct from type-type identity theory (see 1960, SS54, and
Davidson 1980). I may think of Fermat's Last Theorem at
many times, over the years, and on each occasion that act is
identified with the physical state that I am in at the time.
Token-token identity theory does not claim that these physical states
have anything in particular in common, still less that all acts of
thinking about the theorem, including those of other people, have
something in common. There is no claim that each act of thinking about
the theorem can be identified with, e.g. a repeatable pattern of the
firing of brain cells (hence the monism is 'anomalous').
It is enough for Quine's purposes that each particular act of
thinking can be identified with a physical object. This ontological
physicalism might seem almost trivial; Quine speaks of it as
"[e]ffortless monism ... form without substance"
(1995, 85). The view does, however, exclude disembodied minds and
mental entities; Quine thinks that is no loss. Note that the view can
be construed either as eliminating mental entities or simply as
identifying them with physical objects. Quine prefers the latter
phrasing but thinks there is no real difference here; cf. 1960,
265.



On the issue of the admissibility of predicates, Quine's
physicalism is more complicated. (This is in keeping with his general
idea that we can think of the predicates, rather than the ontology, as
"where the metaphysical action is"; 1976, 504). The
requirement here is that the difference between a predicate's
being true of a given object and its being false of it should, in all
cases, be a physical difference: "nothing happens in the world,
not the flutter of an eyelid, not the flicker of a thought, without
some redistribution of microphysical states.... physics can
settle for nothing less" (1981, 98). If a predicate such as
"...is thinking about Fermat's Last Theorem"
picks out genuine events in the world then there is a physical
difference between its being true of a person and its not being true
of them: a fact of the matter.



A difficulty in making sense of this is that the idea of a
*physical* fact is not definitively specifiable. To tie the
idea too closely to current physics would rule out fundamental changes
in that subject; to leave it floating free might seem to allow
anything at all to qualify. But clearly Quine does not mean just any
subject that someone might call by the name "Physics". He
has in mind a subject continuous with our physics, alike or superior
in its coherence and in its explanatory power. (In particular, it
would not have "an irreducibly psychological annex":
1986a, 403f.). If phenomena occurred which could not be explained by
any theory of that kind, then Quine's physicalism would go by
the board.



The most controversial application of this view is to mental
phenomena. Within that realm, Quine focuses on attributions of
propositional attitudes, statements that so-and-so believes that
such-and-such, or hopes that, or fears that, etc. (One reason for this
focus may be that his interest is primarily in human knowledge;
another that some other mental states, such as pain, can perhaps be
accounted for by identifying them with certain types of
neurophysiological events.)



Propositional attitudes also raise a different kind of issue.
Attributions of such attitudes violate extensionality. If Mary is the
Dean, still Tom's believing that the Dean sings well is not the
same as his believing that Mary sings well, since her accession to the
Deanship may be unknown to him. Quine escapes this sort of problem by
taking an attribution of belief to express a relation between the
believer and a *sentence*, understood to be, in the usual case,
in the language of the ascriber (not the language of the believer,
where the languages differ).



It is worth noting the idea of another sense of belief-ascription
which would not be vulnerable even *prima facie* problems of
extensionality: so-called *de re* belief, as distinct from
*de dicto* belief. In the 1950s Quine argued that there must be
such a sense. In the late 1960s, however, he abandoned the idea, for
lack of clear standards of when it is correct to ascribe a *de
re* belief to someone. (See Quine 1956 for a statement of the
distinction, and Quine 1973 for retraction.) Other philosophers,
however, continue to hold the idea. (See, for example, Kaplan 1968,
Kripke 1979.)



Construing attributions of belief as statements of attitudes towards
sentences gives them a syntax and an ontology that Quine can accept.
That does not, however, show that the idiom "*A* believes
that *p*" satisfies his physicalistic criterion, i.e.
that all statements of this form correspond to (physical) facts. The
matter is complicated. Quine certainly accepts that most uses of this
idiom are factual. The relevant facts are neurophysiological states of
the person concerned, and those states are causally connected with
actions which the person performs, or would perform under certain
circumstances, and which we would count as manifestations of the
belief, or lack of belief. (Assenting or dissenting when asked is one
such action, but only one among a myriad.) In cases where we have
evidence for or against the ascription of a belief to someone, the
evidence consists in behaviour and there are presumably
neurophysiological states which explain the behaviour. Those states
are not in practice specifiable in neurophysiological terms.
Nevertheless, the person's being in those states is the physical
fact in which the truth of the ascription consists. Even where there
is no behaviour of the relevant kind, there may still be dispositions
to behave in those ways under certain unrealized circumstances. The
dispositions are the physical states in which the truth of the
ascription consists. So in most cases where we ascribe belief, there
is a fact of the matter which makes the ascription true or false.
(More on dispositions a few paragraphs hence.)



The belief idiom, however, also lends itself to use in other cases,
where there is no fact of the matter. These are not merely cases in
which we have no evidence. They are cases in which no behavioural
tests which we might have carried out would have supplied evidence,
cases in which there simply is nothing in the subject's
neurophysiology, and hence nothing in their actual or potential
behaviour, which would decide the matter. Quine puts the point like
this: "Some beliefs, perhaps belief in the essential nobility of
man qua man, are... not readily distinguishable from mere lip
service, and in such cases there is no fact of the matter.... But
most attributions or confessions of belief do make sense.... The
states of belief, where real, are... states of nerves."
(1986a, 429)



Quine explicitly acknowledges that we could not in practice manage
without idioms of propositional attitude, and that most uses of such
idioms are entirely unobjectionable. But such idioms allow the
formation of sentences which do not correspond to facts of the matter.
For that reason, Quine excludes them from regimented theory; they are
not be used when we are concerned with "limning the true and
ultimate structure of reality" (1960, 221). (Some philosophers
might insist: 'Either you accept the concept of belief or you
don't'. Quine would not agree; see 1986e for closely
related remarks about the idea of knowing who someone is.)



A somewhat similar point can be made about subjunctive or
counterfactual conditionals. Some are factual, but the general
counterfactual idiom allows for the formation of sentences which are
not factual. Like propositional attitudes, counterfactual conditionals
have an important role in our practical lives. They are also closely
connected with dispositions which, as we have seen, play a central
role in Quine's account of language and how it is learnt. The
connection is easily seen: to call an object fragile is to say that it
*would* break if it *were* dropped onto a hard surface
from a significant height.



Quine does not accept the general counterfactual idiom, "if
*X* were to happen then *Y* would happen", as part
of regimented theory. As in the case of belief, the unrestricted use
of this idiom allows us to form sentences whose truth-conditions are,
at best, unclear. A famous example is the pair, presumably alluding to
the Korean war of the early 1950s: "If Caesar were in charge he
would use the atom bomb"; "If Caesar were in charge he
would use catapults" (see Quine 1960, 222); they seem equally
plausible but they cannot both be true (for a response, see Lewis
1973). In such cases, we have no reason to think that some (physical)
fact is being claimed. Many dispositions, however, are perfectly
acceptable by Quinean standards. To call the glass fragile is to
attribute to it a structure which would lead its breaking under
certain circumstances; the structure is a physical state, even if we
cannot in practice specify it in physical terms.



Quine claims that the dispositions he relies on in his account of
language are like the case of fragility rather than the case of
Caesar. The disposition to assent to an observation sentence when
receiving certain stimulations is a physical state of the person
concerned; in particular, presumably, of his or her brain. The claim
that a given person has such a disposition is thus a claim about the
state of a physical object. It is, moreover, a claim that we can test,
at least under favourable conditions. There is no reason to exclude it
from regimented theory.



Another idiom which Quine famously excludes from regimented theory is
that of modality, statements that such-and-such *must* be the
case, or *cannot* be the case, and so on. Such idioms have been
the subject of much discussion on the part of Quine and (especially)
his critics; the discussion here will be very brief. Technically,
there are similarities with the case of belief. There is *prima
facie* violation of extensionality which can, however, be avoided
by taking necessity to apply to sentences; some philosophers have
claimed that there is a *de re* sense of necessity which does
not lead to even *prima facie* violations of extensionality.
Quine allows that modal terms have a legitimate ordinary language use
('possible' is sometimes used to mean something like: we
can't rule it out; see 1966, ch. 10). But his attitude towards
the philosophical use of the idea of modality, dividing truths into
the necessary and the possible, is far less sympathetic than his
attitude towards belief; he is particularly unsympathetic towards the
idea of *de re* necessity, which he sees as requiring
"Aristotelian essentialism" (Quine 1953, 155).



What frames these critical points about necessity is that Quine holds
that regimented theory, the best and most objective statement of our
knowledge, simply has no need for that notion. The benefit of
including such idioms in regimented theory is not worth the cost in
unclarity that it would bring.


### 5.3 Truth



Truth, in Quine's view, is immanent, as opposed to transcendent.
In accord with his fundamental naturalism, he sees judgments of truth
as made from within our theory of the world. For this reason, he
sympathizes with what is sometimes called disquotational theory of
truth: to say that a sentence is true is, in effect, to assert the
sentence. Two qualifications must be made. First, the disquotational
view is not a *definition* of "is true". It enables
us to eliminate the predicate from contexts in which it is applied to
a finite number of specific sentences, but not from contexts where it
is applied to infinitely many. Contexts of the latter kind are of
particular importance to logical theory. We say, for example, that a
conjunction is true just in case both conjuncts are true; here
"is true" cannot be eliminated. (Unless, indeed, we ascend
to a metalanguage and give a definition of truth for the object
language that we are concerned with, following Tarski 1933.) Second,
calling an eternal sentence true is in one way unlike asserting it. If
we subsequently change our verdict on it we say that we used to
believe it but now we don't. We do not, however, say that it
used to be true but now it isn't; rather we say that it was
never true. Quine, however, sees this as simply a point of usage, with
no particular philosophical implications.


## 6. Underdetermination of Theory by Evidence; Indeterminacy of Translation



In this section we take up two ideas much discussed by commentators.
Neither is essential to Quine's overall philosophy, although in
each case, but especially in the case of indeterminacy, the opposite
claim has been made. (See Ebbs, 1997; for a defense of the position
taken here, see Hylton, 2007.)


### 6.1 Underdetermination



The basic idea of underdetermination is that two or more rival
theories might have all the same observational consequences, and thus
be empirically equivalent. Theory would thus be underdetermined by
observation. This might be held to call realism into question (as in
van Frassen 1980). Quine finds underdetermination harder to make sense
of than might appear and, in any case, does not see a threat to
realism.



In Quine's idealized schematization of the relation between
theory and evidence, evidence for theory consists of observation
categoricals. (These latter can, in turn, be tested by observing or
contriving situations in which relevant observation sentences are
true.) The case which most obviously poses a potential threat to
realism is that of a final global theory, a perfected and completed
version of our own. What if there are two or more such theories,
equally simple, each of which implies *all* true observation
categoricals? (Note that the theory will not be implied *by*
all the true observation categoricals; apart from other
considerations, some sentences of the theory will essentially contain
terms which do not occur in observation categoricals.)



Quine is often thought to accept underdetermination. But in fact he
holds that there is considerable difficulty in making non-trivial
sense of the doctrine. He identifies theories with sets of sentences,
not with sets of sentence-meanings (propositions). So we can quite
trivially obtain an empirically equivalent alternative to any theory:
simply spell one of the theoretical terms differently at every
occurrence. Strictly speaking, the result is a different set of
sentences which implies all the same observation categoricals (1975a,
319). The difference from the original theory, however, is merely
orthographic; this possibility is clearly not of any philosophical
significance.



A closely related point can be made in terms of translation.
Translation of observation categoricals is quite unproblematic in
principle. So we can count two theories as empirically equivalent not
merely if they imply the same observation categoricals but also if
they imply intertranslatable observation categoricals. So classical
physics as formulated in English (say) would, by this criterion, count
as empirically equivalent to classical physics as formulated in
German, yet the two formulations are, strictly speaking, different
theories. Quite generally, any theory is empirically equivalent to its
translation into any other language. But this fact is also not of any
great philosophical significance, and certainly poses no threat to
realism.



In order to threaten realism, a version of underdetermination would
thus have to assert that our postulated complete global theory of the
world has empirically equivalent alternatives and that no translation
from one theory to the other is possible. Since the predicates of the
theory are its only non-logical vocabulary, this is equivalent to
saying that we cannot obtain one from the other by reconstruing the
predicates of the theory. Quine comments: "This, for me, is an
open question." (1975a, 327). Much of his subsequent discussion
of underdetermination takes place in terms of the weaker idea that our
theory might have empirically equivalent alternatives and that
"*we would see* no way of reconciling [them] by
reconstrual of predicates" (*loc. cit,* emphasis added;
cf. also 1990a, 97).



If some version of underdetermination were true, how should we
respond? This is an issue on which Quine has not merely changed his
mind but vacillated, going back and forth between what he calls the
"sectarian" and the "ecumenical" responses.
The sectarian response is to say that we should not let the existence
of the alternative in any way affect our attitude towards our own
theory: we should continue to take it seriously, as uniquely telling
us the truth about the world. (We are assuming that the two theories
possess all theoretical virtues to equal degree; clearly Quine would
say that if one theory were superior in some way then we would have
reason to adopt it.) The ecumenical response, by contrast, counts both
theories as true. In almost his last word on the subject he suggests
that there may be little at stake since the "fantasy of
irresolubly rival systems of the world" takes us "out
beyond where linguistic usage has been crystallized by use"
(1990a, 100f).



Quine can afford to vacillate because, in his view, nothing very much
turns on the issue. In particular, he never holds that
underdetermination, in any version, would threaten realism; at no time
does he suggest that it casts doubt on the truth of our theory. That
is not what is in question between the sectarian and the ecumenical
positions; all that is in question is whether the alternative theory
should *also* be counted as true. Nor is this surprising. The
terms in which underdetermination is stated, such as observation
categoricals, are part of our theory, as would be the demonstration
that another theory was empirically equivalent. The point here is the
naturalism which we have emphasized throughout. Nothing in our
epistemology pronounces on the status of theory from an independent
standpoint; to the contrary: it presupposes the truth of our theory.
This central idea is not cast in doubt by underdetermination. (See
Severo 2008; for criticism, see Moore 2015 and for a rejoinder to
Moore see Kemp 2016.)


### 6.2 Indeterminacy of Translation



The general claim of the indeterminacy of translation is that there
might be different ways of translating a language which are equally
correct but which are not mere stylistic variants. The claim includes
what one might think of as the limiting case of translation, that in
which a given language is 'translated' into itself.



Some philosophers hold that the idea of indeterminacy is absurd, or
that it amounts to an extreme form of scepticism about whether we ever
understand one another, or whether correct translation is possible at
all. (See for example Searle, 1987; for a reply, see Follesdal,
1990.) It is not hard to see how such opinions arise. One picture of
communication is like this: you have an idea, a determinate meaning,
in your mind and convey it to me by your utterance. To those who have
that picture, indeterminacy threatens the whole idea of communication,
for it suggests that the conveying is always vulnerable to drastic
failure. In the case of translation, the analogous view is that
synonymy, or sameness of meaning, is the criterion of correct
translation; in that case, indeterminacy may appear as a denial that
translation is possible at all.



Such views, however, take for granted a view of communication, or of
translation, which is very far from Quine's. For Quine, the
criterion of successful communication, whether or not it involves
translation, is fluent interaction, verbal and nonverbal:
"Success in communication is judged by smoothness of
conversation, by frequent predictability of verbal and nonverbal
reactions, and by coherence and plausibility of native
testimony." (1990a, 43) This is a third person or external view
of language and communication, as required by Quine's
naturalism. From this point of view, talk of synonymy and of ideas in
the mind is simply a theoretical gloss which is (at best) in need of
justification. Quine doubts that the gloss is justifiable; scepticism
about the theorizing, however, is not scepticism about the data.
Smooth communication certainly occurs, sometimes in cases where
different languages are involved. Quine says nothing that casts doubt
on the idea that successful translation (by his criterion) is
possible; his claim, indeed, is that it may be possible in more than
one way.



At this point we need to distinguish two kinds of indeterminacy. Quine
introduces the general idea of indeterminacy, in Chapter Two of
(1960), without explicitly distinguishing the two, but subsequently
comes to treat them quite differently. The first is *indeterminacy
of reference*: some sentences can be translated in more than one
way, and the various versions differ in the reference that they
attribute to parts of the sentence, but not in the overall net import
that they attribute to the sentence as a whole. (Quine uses the terms
"ontological relativity" and "inscrutability of
reference", as well as "indeterminacy of reference".
Some philosophers have sought to distinguish these doctrines, but in
later work Quine makes it clear that he uses the terms simply as
different names for the same thing. See Ricketts 2011, Roth, 1986, and
Quine 1986d.) To use an example which has become famous, a given
sentence might be translated as "There's a rabbit"
or as "Rabbithood is manifesting itself there" or as
"There are undetached rabbit parts", or in other ways
limited only by one's ingenuity. All that is needed is what
Quine calls a proxy function, which maps each object onto another
object and each predicate onto one which is true of a given
proxy-object if and only if the original predicate is true of the
original object. For terms referring to physical objects, he suggests,
we can take the proxy-function to map each object onto its space-time
complement. The change to the translation of singular terms and the
change to the translation of predicates cancel out, leaving the
overall significance of the sentence unchanged. The claim of
indeterminacy of reference is not in any way a claim about what goes
on in the language-user's mind (*pace* Wright 1997).
(Note that it will not help to ask the person we are translating
whether she means to refer to the family dog or to its space-time
complement: her answer is subject to the same indeterminacy.)



Indeterminacy of reference is akin to a view of theoretical entities
put forward by Ramsey: that there is no more to such an entity than
the role that it plays in the structure of the relevant theory (see
Ramsey, 1931). For Quine, however, the point holds for all objects,
since he "see[s] all objects as theoretical.... Even our
most primordial objects, bodies, are already theoretical" (1981,
20). Quine holds, moreover, that considerations akin to those of the
previous paragraph amount to a "trivial proof" of
indeterminacy of reference (1986c, 728).



The second kind of indeterminacy, which Quine sometimes refers to as
*holophrastic indeterminacy*, is another matter. Here the claim
is that there is more than one correct method of translating sentences
where the two translations of a given sentence differ not merely in
the meanings attributed to the sub-sentential parts of speech but also
in the net import of the whole sentence. (Hence the two translations
would express different propositions, in the abstract sense, or
different Fregean *Gedanke*; Quine claims that undermining
these ideas was part of his motivation in developing the doctrine; see
1990d.) This claim involves the whole language, so there are no
examples, except perhaps of an exceedingly artificial kind. There is
also nothing resembling a proof; in some late works, indeed, Quine
refers to it as a "conjecture" (1986c, 728). At some
earlier points, he seems to think that sufficiently clear-headed
reflection on what goes into translation will suffice to make the idea
at least plausible. All that can be required of a method of
translation is that it enables us to get along with the speakers of
the other language: why should there *not* be more than one way
to do it?



Arguments have been offered for holophrastic indeterminacy based on
the idea of underdetermination of theory by evidence (by Quine himself
in his 1970) . Perhaps there is determinate translation of observation
sentences, and thus of observation categoricals. Still, if each two
distinct theories is compatible with all observational truths, surely
we could plausibly attribute either theory to the speaker of the other
language. The weakness of this kind of argument is that translation
must presumably preserve more than links between sentences and
stimulations, as captured by observation sentences; it must also
preserve links among sentences, links which make it more or less
likely that a person who accepts a given sentence will also accept
another. Could there be methods of translation which preserved both
kinds of links but nevertheless yielded different results?
Quine's term "conjecture" seems apt.



Given the interpretation advanced in section 3, above, indeterminacy
is not crucial for Quine's rejection of the sort of use that
Carnap makes of the idea of analyticity. He has other arguments on
that score, as we saw. More generally, on the interpretation advanced
here, indeterminacy is not a crucial part of Quine's overall
view. His coming to speak of it as conjectural, while not questioning
other parts of his philosophy, suggests that he would accept this. If
we were sure that translation is determinate, we could perhaps use the
idea to define a notion of synonymy. (Agnosticism here favours the
contrary position.) And, as Quine has indicated, we could then define
the meaning of an expression as the set of synonymous expressions.
Such a notion of meaning might make some difference. It might, for
example, provide a criterion of identity which enabled us to accept
beliefs as entities. It would not, however, play the most important
roles in which philosophers have cast the idea of meaning. In
particular, it would not play a role in the explanation of how we
understand our language, or of how communication between persons takes
place.


## 7. Quine's place in the history of philosophy



In the 1930s and 1940s, many scientifically-oriented philosophers
tended to assume some form of Logical Empiricism. One important aspect
of Quine's influence on the course of philosophy is that he
called that view or nexus of views into question (see section 3,
above). Some of his criticisms are detailed and technical. His target,
however, was not a technical detail but the fundamental idea of
Logical Empiricism, that there is a distinction between analytic
truths and synthetic truths which can account for *a priori*
truth. After Quine's work of the early 1950s, philosophers, even
those who did not accept his detailed arguments could no longer take
it for granted that some form of Logical Empiricism is correct. This
was a very major change among scientifically-oriented
philosophers.



Quine's rejection of Logical Empiricism leads him to two
(connected) views which have been extremely influential. First, he
rejects the idea of a distinction between philosophy on the one hand
and empirical science on the other hand. To the contrary: he sees
philosophy as essentially in the same line of work as science, but
mostly concerned with more theoretical and abstract questions. This is
an integral part of his naturalism. Second, his criticism of Carnap,
and of the Principle of Tolerance in particular, opens the way for
something that might be called metaphysics: for very general
reflections on the nature of the world, based on the best scientific
knowledge that we have and on claims about how that knowledge might be
organized so as to maximize its objectivity and clarity.



Both of these Quinean views, his naturalism and his acceptance of
something like metaphysics, correspond to very important developments
within analytic philosophy over the past half-century. His influence
has surely played a significant role here. (In the case of
metaphysics, in particular, it is notable that two leading figures,
Saul Kripke and David Lewis, were students of Quine's.) For the
most part, however, those Quinean doctrines have led to work to which
Quine himself would be strongly opposed.



In the case of naturalism, many philosophers have welcomed the idea
that they are free to use concepts and results drawn from empirical
science. Fewer have accepted that philosophy should also be
constrained by scientific standards of clarity, of evidence, and of
explanatoriness. The result is that while views which claim to accept
naturalism are common, those which accept Quine's standards of
what counts as reputable naturalistic philosophy are not.



The case of metaphysics is similar but perhaps more extreme. Quine
accepts that the philosopher is in a position to make very general
claims about the world (that there are sets but not properties, for
example). In his hands, such claims are answerable to the idea of a
total system of our scientific knowledge, regimented so as to maximize
clarity and systematicity. Many philosophers have welcomed the freedom
to speculate about the nature of the world but have not accepted
Quine's constraints on the process. The result is a flourishing
of metaphysics, often based on ordinary (unregimented) language or on
the alleged deliverances of 'intuition'; much of this work
would be anathema to Quine. (See Rosen 2014.)



On the one hand, then, Quine's work has been extremely
influential and has done much to shape the course of philosophy in the
second-half of the twentieth century and into the twenty-first. On the
other hand, much of the work directly or indirectly influenced by
Quine is of a sort that he would have thought quite misguided.