## 1. Introduction



In the philosophy of mind, *externalism* is the view that what
is going on inside an individual's body does not always, on its
own, fix what is going on inside that individual's mind. The
*mind*, in this sense, simply denotes the totality of mental
occurrences undergone by an individual at any given time. The
*body*, in this sense, delineates the biological boundaries of
the individual which, in creatures such as us, coincide with the
individual's skin and, of course, includes the brain,
traditionally taken as the crucial determinant of an
individual's mental life. Thus, externalism is the view that an
individual's bodily (including neural) events, states,
processes, etc. do not always, on their own, determine the mental,
states, processes had or undergone by that individual. The qualifier
*not always* permits there to be cases--perhaps
many--in which mental occurrences are fixed by bodily
occurrences. Externalism, generically at least, is merely committed to
the claim that this does not *always* happen. The qualifier
*on its own* is intended to convey that even if an
individual's bodily occurrences do not *completely*
determine which mental occurrences are had or undergone by that
individual, the former will at least *partially* determine the
latter and, indeed, can play an important role in such determination.




Externalism appears in two major forms. *Content externalism*
is externalism about mental *content*--the content of
mental states. It claims that the contents of at least some mental
states are not solely determined by occurrences falling within the
biological boundaries of that individual that has them. Since mental
states that have content are typically individuated by that content,
this entails that which mental states an individual has is not
completely determined by occurrences falling within the biological
boundaries of that individual. *Vehicle externalism*, more commonly known as the thesis of the *extended mind*, is externalism about the *vehicles* of mental content. According to the thesis of extended mind, the vehicles of mental content--roughly, the physical or computational bearers of this content--are not always determined or exhausted by things occurring inside the
biological boundaries of the individual. Content externalism and extended mind are logically independent views, and it is not uncommon to find adherents of one view denying the other. These two forms of externalism diverge sharply not simply because they are externalism about different things--contents and vehicles,
respectively--but also because they have different
conceptions of this failure of determination. If mental contents are not determined solely by what is occurring inside the biological boundaries of an individual, this is quite different from the way in which the vehicles of content are not determined solely by what is occurring inside these boundaries. In other words, each form of
externalism differs not only in what it claims to be external, but
also in what it means by "external".


## 2. Historical Antecedents



Externalism--whether of content or vehicle--is often viewed
as a peculiar eruption of late twentieth-century analytic philosophy.
This, however, is historically myopic. Cognate views with fairly clear
externalist credentials have been advanced and defended much earlier
than this, and in some of the defining works of twentieth-century
philosophy (see Rowlands 2003: Chapters 3&4). Wittgenstein (1953)
argued that meaning something by a sign does not consist in an inner
state or process. Rather, the possibility of such meaning depends
essentially on the existence of a *custom* or *practice*
of using a sign in given way, and the *mastery of a
technique*--i.e., the ability to adjust one's use of
the sign to bring in into accordance with this custom. According to
the dominant--*community*--interpretation of the
notion of a custom, this entails that the possibility of meaning
something by a sign is dependent on the existence of a practice
external to the individual meaner, and that what this individual means
by a sign on any given occasion depends, at least in part, on this
external practice. As we shall see, this social version of content
externalism was later developed, powerfully, by Burge (1979,
1986).



There are earlier views that are, at least, closely aligned with
externalism. Sartre (1943 [1957]) argued that consciousness--his
term for intentional mental acts in general--is *nothing*
in the sense that it exists only as a pure directedness towards the
world, and is essentially dependent for its existence on the objects
to which it is directed. As a consequence, Sartre claimed,
consciousness has "no content". What he meant by this that
what we, today, would call the contents of intentional acts are
always, necessarily, outside those acts--transcendent items in
the world rather than immanent things inside consciousness. Content
externalism seems to be a trivial implication of this. If it were
possible to transplant a consciousness from one world to
another--a staple, as we shall see, of later externalist
literature, but which may or may not make sense on Sartre's
view--the contents of this consciousness would necessarily
change. The reason this may not qualify as externalism in the standard
sense, however, is that Sartre also defended a revisionist conception
of the body. The *body-as-lived*, Sartre argued, is not
identical with the *body-as-object*--the way the body is
conceived of in the formulation of externalism. Rather, the
body-as-lived is revealing activity whose boundaries in no way
coincide with those of the body-as-object. Thus, rather than being a
straightforward form of externalism, Sartre's view may better be
regarded as an abandoning the categories in terms of which the ideas
of externalism--and its oppositional counterpart,
internalism--are formulated. The same is true of Heidegger (1927
[1962]), to whom Sartre's discussion of the body was heavily
indebted. Heidegger urges us to think of human
reality--*dasein*, the characteristic type of being
possessed by humans--not as a biological organism but, rather, as
a network of natural and social practices. Humans minds, to the extent
they have any place in this scheme, would certainly not reside in
human bodies. However--and this is why it does not qualify as
externalism in the usual sense--neither do bodies. (But see
Wheeler 2005, for a defense of extended mind grounded in
Heidegger's work.)



Whether or not they can ultimately be characterized as externalist,
the views of Wittgenstein, Sartre and Heidegger play an important role
in contextualizing the later development of externalism. Like
externalism, they all occupy a position that can be labeled
*anti-Cartesian*. They are all opposed to the idea that the
mental processes had by an individual are always, and completely,
determined by what is going on inside that individual's body (or
they expand the idea of the body in non-Cartesian ways, as in the case
of Sartre and Heidegger). This type of view is not peculiar to
philosophy. In psychology, expressions of the idea can be found in the
work of the Soviet psychologists, most notably Vygotsky (1934 [1962]), and Luria and Vygotsky (1930 [1992]) and later in James Gibson's (1966, 1979) development of an *ecological psychology* (see also Donald 1991 for a more recent development in this tradition). The roots of this anti-Cartesianism are not only
broad but deep, predating Heidegger, and indeed the twentieth century.
Gallagher (2018) argues that versions of this can be found in American
pragmatism. It may be that the ultimate roots of this sort of anti-Cartesianism lie in Hegel (Crisafi & Gallagher 2010; Boldyrev
& Herrmann-Pillath 2013). Whether or not this is correct,
externalism--in either form--is best regarded as less an unprecedented eruption, and more as a recent expression of this
historical tradition of anti-Cartesian thought.


## 3. Content Externalism



Many mental states or acts (some think *all* mental states or
acts) are intentional in that they are about something or other. You
do not simply think; you think *something*. You do not merely
believe or desire; you believe or desire something. This something
that you think, believe, desire or, for that matter, hope, fear,
expect, anticipate, and so on, is the *content* of the
thinking, believing, desiring, hoping, fearing, expecting and
anticipating. *Content externalism*--sometimes known as
*semantic externalism*, since content is sometimes known as
semantic content--is externalism about the content of mental
states or acts.



Content externalism is typically understood as a claim of
*dependent possession* which is, in turn, grounded in a more
basic claim of *individuation dependence*. The idea of
dependent possession is straightforward: whether or not an individual
can entertain the content that *p* (for example, by having a
belief, thought, desire or other propositional attitude with this
content) depends on the nature of that individual's environment
(and facts about its relation to that environment). It is not possible
for an individual to entertain this content unless the environment
contains the requisite objects, properties, facts, events etc. of a
certain sort (McGinn 1989). Content externalism is the claim that, at
least in some cases, though not necessarily all, the possession of a
mental state with a given content is environmentally dependent in this
sense.



This claim of dependent possession is derivative upon a further claim:
*individuation dependence*. The general idea of individuation
dependence is that the identity of an entity, as an entity of a
particular kind *s*, depends upon things (objects, properties,
facts, etc.) distinct from it. A planet is individuation dependent on
a star around which it orbits in the sense that without this star, and
resulting orbit, it would not be a planet but some other kind of
celestial object. The identity of a particular celestial body
*as* a planet is dependent on the star and orbit, items
distinct from the planet itself. The planet is, in this sense,
individuation dependent on the star (Macdonald 1990). A particular
skin disturbance correctly classified as sunburn is individuation
dependent on solar radiation in the sense that it can be sunburn only
if it produced by solar radiation (Davidson 1987). Thus, the
*identity* of a skin disturbance as an instance of sunburn
depends on its standing in an appropriate relation to ultraviolet
radiation, and it cannot be an instance of sunburn unless it stands in
this relation. Sunburn is, in this sense, individuation dependent on
solar radiation



Content externalism is the thesis that at least some mental content
is, similarly, individuation dependent on the nature of the
environment, understood as a collection of circumstances that reside
outside the biological boundaries of the individual. The identity of
given content *p* is dependent on circumstances that lie outside
the biological boundaries of the (objects, properties, facts, events,
etc.) of the individual who entertains this content.


### 3.1 Arguments for Content Externalism



Content externalism is most commonly associated with two vivid thought
experiments, presented in the 1970s; the first by Hilary Putnam
(1975), and the second by Tyler Burge (1979).


#### Putnam's Twin Earth Thought Experiment



Imagine a planet, a *twin earth*. There are a few things you
should know about this planet. First, it duplicates earth in almost
every respect. On twin earth, at this very moment, a twin version of
you is reading a twin version of this *Stanford Encyclopedia*
entry, which has been written by a twin version of me. The twin
version of you is your exact, molecule-for-molecule, duplicate.
Second, the only difference between earth and twin earth is this: on
twin earth, the substance that sits in oceans, flows in rivers, and
comes out of faucets is not water. It is not water, because it is not
made up of two parts of hydrogen to one part of oxygen. In fact, it is
not made of hydrogen and oxygen at all but, rather, some other
elements entirely absent on our earth. Nevertheless, third, this
substance looks, tastes, and feels exactly like water does to people
on our earth, and is used in the same way. Finally, this thought
experiment is set in 1750 (and, a corresponding twin 1750), before
people had any idea of the underlying molecular structure of
substances such as water.



Suppose you say, or write, the sentence, "Water is wet".
Your twin produces a sentence with the same phonetic or syntactic
form: "Water is wet". Do the two sentence-tokens have the
same meaning? Putnam's answer is that they do not. This answer
will be found inviting by anyone who thinks of meaning as a matter of
*reference*, or *truth-makers,* or
*truth-conditions*, or, in short, anyone who thinks that the
meaning of a term or sentence is, at least in part, a matter of its
relation to some kind of worldly correlate. The *reference* of
the syntactic/phonetic form "water" differs between you
and your twin. When you utter the sentence, you are making a report
about water--a substance composed of hydrogen and oxygen. But
your twin's corresponding report is about the substance on twin
earth. For purposes of identification, we can call this substance
*twater*, but the twin earthlings, of course, call it no such
thing. They speak twin-English, and so refer to this substance with
the syntactic/phonetic form "water". Moreover, your
utterance and your twin's utterance are both true, but different
facts *make them true*. Your utterance is made true by a fact
about water, whereas your twin's utterance is made true by a
fact about twater. The *truth-conditions* of the utterances
also differ. For your utterance to be true, water must be wet. For
your twin's utterances to be true, twater must be wet. Thus,
from the perspective of theories that think of meaning in terms of
these kinds of worldly correlates--reference, truth-makers,
truth-conditions--there are good reasons for endorsing
Putnam's conclusion.



As McGinn (1977), and Burge (1979), have pointed out, this claim can
be extended to the content of propositional attitudes. In ascribing a
propositional attitude--such as a thought, belief,
desire--to a person, we use a "that"-construction,
followed by an embedded sentence. The sentence is commonly thought to
express the content of the propositional attitude: that is, the
meaning of the sentence is identical with the content of the
propositional attitude. Therefore, if the sentences expressed by you
and your twin have different meanings, it is difficult to avoid the
conclusion that the contents of your thoughts, beliefs and desires
also vary. However, beliefs, and other propositional attitudes are
individuated by their contents. The belief that grass is green is a
different belief from the belief that snow is white because their
contents are different. Therefore, if the contents of the beliefs had
by you and your twin are different, then so too are your beliefs.



Despite its seemingly outlandish nature, this twin earth thought
experiment is just a way of making graphic a simple point. You and
your twin are, as a matter of stipulation, molecule-for-molecule
duplicates. Thus, everything situated inside your head (and biological
boundaries more generally) is, by stipulation, qualitatively (if not
numerically) identical. Nevertheless, your beliefs (and other
propositional attitudes) differ. The principle that emerges is, then,
this: if you fix what is going inside the head (and biological
boundaries more generally) of an individual and vary his or her
environment, some of that individual's mental states will vary
with variations in the environment even though everything in his or
her head remains the same. Therefore, what occurs inside the head is,
in this sense, not sufficient to determine or fix everything that
occurs in the mind.



Despite some initially over-exuberant formulations of Putnam
(1975)--of the "Cut the pie any way you like, meaning just
ain't in the head", variety--the correct conclusion
of this thought experiment does not concern the *location* of
(some) mental states but, rather, a claim about their
*individuation*. External individuation does not entail
external location. Sunburn, as Davidson (1987) pointed out, is
externally individuated: individuation dependent on factors that lie
outside the skin. Nevertheless, it is still located on the skin. That
some mental states are individuation dependent on circumstances that
exist outside the skin of an individual does not entail that those
mental states are located outside the individual's skin.


#### Burge's "Arthritis" Thought Experiment



Imagine a person, let us call him Larry, who has a number of beliefs
about arthritis. He believes that he has arthritis, that he has had it
for years, that arthritis can be very painful, and that it's
better to have arthritis than pancreatic cancer, and so on. He also
believes he has arthritis in his thigh. This belief, according to
Burge, is (a) an arthritis-belief and (b) false. It is false because
arthritis is an affliction of the joints only. But why is it an
arthritis-belief--a belief about arthritis? Burge's answer
is that Larry inhabits a linguistic community made up of people who
use the term "arthritis" in a certain way, and Larry would
allow himself to be corrected by expert members of that community.
Thus, when a doctor tells him, "No, that's not arthritis
you have. Arthritis is an affliction of the joints". Larry would
be inclined to accept this, and revise his belief accordingly.



Now we imagine Larry in a counterfactual situation. Counterfactual
Larry is type-identical with Larry in point of functional profile,
behavioral dispositions, and experiential history (all
individualistically specified--that is, specified in such a way
that does not presume the existence of anything outside Larry). The
counterfactuality of the situation pertains only to Larry's
linguistic community. In this counterfactual situation, the phonetic
or syntactic form "arthritis"--as used by physicians,
lexicographers, and competent laypersons--applies not only to an
affliction of the joints but also to various other rheumatoid
ailments. That is, in the counterfactual situation, the correct use of
the term "arthritis" encompasses Larry's actual
misuse. In this counterfactual situation, Burge argues, Larry
possesses a true belief about what is going on in his thigh but,
crucially, it is *not* an arthritis-belief. Rather, he has
beliefs about a distinct condition--*tharthritis*, an
amalgam of arthritis and rheumatism, as we might regard it.



If this is correct, Larry's beliefs vary between actual and
counterfactual situations. Larry, however, is identical in both
situations. The only difference lies in the differing natures of his
linguistic communities--specifically, the differing uses of the
word-form, "arthritis". As in Putnam's
thought-experiment, the difference in meaning again stems from a
difference in extension of a term, resulting in different
truth-conditions, truth-makers, and the like. But in Putnam's
case, the differences stem from differences in the natural
environment. In Burge's thought experiment, these differences
stem from differences in linguistic practice. As in the Putnam case,
the argument can easily be extended to the contents of propositional
attitudes, and Burge, unlike Putnam, explicitly endorses this
extension.


### 3.2 Responses to Content Externalism



Responses to content externalism divide into several kinds. The first
type of response simply regards externalism as insufficiently
supported by the kinds of arguments developed by Putnam and Burge,
either because their conclusions are non sequiturs or because the
arguments are deficient in some other way. In this vein, Boghossian
(1997), for example, devises the case of "Dry Earth", a
planet whose inhabitants (who are our intrinsic duplicates) are under
the *illusion* that there is a clear, colorless liquid flowing
out of the faucets and filling the lakes and oceans. According to
Boghossian, externalists are committed to implausible claims
concerning the content of Dry Earthlings' thoughts about this
illusory liquid. (Segal [2000] endorses a variation on this argument
from Dry Earth; see Korman [2006] and Pryor [2007] for externalist
replies.). Crane (1991) argues that in Burge's example, there is
no reason for thinking that Jane has different concepts in the two
situations, as her dispositions remain exactly the same. Crane thinks
that in both situations, Jane lacks the concept of arthritis, but
possesses the concept of tharthritis. Burge was, therefore, mistaken
in attributing to Jane in the actual world the belief that she has
arthritis in her thigh. Georgalis (1999) takes a similar view, as does
Wikforss (2001).



A second type of response objects to these externalist arguments on
broadly methodological grounds that concern the use of thought
experiments, and intuitions more generally, in determining whether
content is wide or narrow. Cummins (1991) argues that empirical
research is needed to find out about the nature of belief, not thought
experiments. Chomsky (1995) holds a similar view. The reliance of
Putnam's and Burge's arguments on intuitions is anathema
to many in the experimental philosophy movement who regard them as
culturally-relative and shifting and, therefore, not philosophically
significant (see, for example, Mallon et al. 2009).



A third type of response questions the legitimacy of the
internalism-externalism debate. Gertler (2012), for example, has
argued that there is no understanding of the distinction between
internal and external properties, and related distinctions such as
that between intrinsic and extrinsic properties, that will correctly
categorize the views we take to be clearly externalist or internalist.
If Gertler is correct, perhaps the most common way of understanding
internalism, as the doctrine that content supervenes on the intrinsic
properties of an individual, is unworkable. She therefore maintains
that there is no genuine dispute at issue in the
internalism-externalism debate, and recommends that philosophers drop
the issue in favor of more well-defined questions. There is, more
generally, an interesting question concerning how to understand the
crucial distinction between a creature's external properties and
those that are intrinsic or internal. Many contributors to the debate
over externalism take internal properties to be *physical*
properties of a creature that do not depend for their instantiation on
any property instantiated outside the boundary of the creature's
body and brain. A difficulty with this understanding of the
distinction, pointed out by Farkas (2003), is that it appears to rule
out the possibility of antiphysicalist internalists. This is ironic,
given that Descartes is often held up as a paradigmatic example of an
internalist about mental content. Williamson (2000) suggests that
internalism can be understood as the doctrine that mental content
supervenes on environmentally-independent phenomenal states, and
Farkas (2003, 2008) makes a similar proposal.


### 3.3 Narrow Content



A fourth response to the arguments for content externalism involves
accepting the force of those arguments but limiting their
significance. According to this type of response, externalism is true
of only one type of content, or of content understood in one
particular way. The kind of content susceptible to Putnam/Burge-style
considerations is *wide* or *broad* content. But there
is, some have argued, another type of content--*narrow*
content--that is immune to these kinds of arguments. In the years
immediately following the publication of Putnam (1975), it was common
to think of narrow content as *phenomenal* content (see, e.g.,
Fodor 1981, 1982; McGinn 1982). The motivation for this is the idea
that even if the contents of you and your twin's beliefs vary,
there is still something that you and your twin have in common. You
both believe, for example, that the colorless, odorless, transparent,
potable etc. liquid in front of you is wet. This strategy faces at
least two problems. First, it conflicts with Burge's claim that
his type of counterfactual earth argument applies to all concepts
known by observational means, a category which includes properties
such as being colorless, being odorless, etc. Second, even if the
first objection can be avoided, it is not clear that we can purge
these phenomenal specifications of content of all concepts immune to
twin earth style considerations (for example, the concept of liquid as
employed in the above specification) whilst retaining sufficient
resources to adequately specify the content of the belief.



Fodor (1987) adopts a different strategy. He agrees that physically
identical individuals have different wide contents when embedded in
different contexts. However, Fodor suggests that their beliefs still
have the same narrow contents, which are functions from contexts to
wide contents. You and your twin share this: a something (it is
impossible to specify what this is) which when plugged in to the
earthly context yields the (broad) content that water is wet, but when
plugged into the twin-earthly context yields the (broad) content that
twater is wet (a content expressed by the twin-earthly "Water is
wet", of course). This strategy has been objected to by
Stalnaker (1989) and Block (1991) on the grounds that narrow content,
as conceived by Fodor, is not, in fact, content at all. If narrow
contents, as Fodor argues, map contexts of thinking onto
truth-conditions, they do not themselves have truth-conditions and
therefore fail to qualify as contents in any recognizable sense.
According to Stalnaker (1989), narrow content is, therefore, nothing
more than *syntax* (understood as functional or computational
role).



There are two more recent developments in semantic theory that can
been used to identify and defend a concept of narrow content. One of
these is *two-dimensional semantics* and its application to the
contents of propositional attitudes (Lewis 1981, Jackson 2007, and
Chalmers 2012). Chalmers, for example, argues that a generalized 2D
semantic framework can be used to isolate an a priori aspect of
meaning that will be shared by you and your twin. You and your twin,
on this view, always have a priori access to the truth-conditions of
your own thoughts or sentences. If correct, this entails that there is
a type or component of content that is not vulnerable to twin earth
manipulation and so might qualify as narrow.



The second development derives from the *phenomenal intentionality
theory*. Advocates of the idea of phenomenal intentionality seek
to ground the intentionality of mental states in phenomenal
consciousness, the subjective, experiential features of those states.
According to this view, phenomenal intentionality is basic, with any
other forms of intentionality derivative upon this basic form (Horgan
& Tienson 2002, Loar 2003, Kriegel 2013). According to many
articulations of the phenomenal intentionality theory (e.g., Siewert
1998; Kriegel 2007, 2011; and Farkas 2008), the content of your
thought and that of your twin is the same and that content is narrow.
These attempts to construct a viable notion of narrow content have
been systematically criticized by Yli-Vakkuri and Hawthorne (2018). If
they are correct, there is no form of content that can be easily
cordoned off from the world, and a thoroughgoing form of content
externalism must, therefore, be true. (See entry on
 narrow mental content
 for more detailed discussion).


## 4. The Significance of Content Externalism



The significance of content externalism is potentially far-reaching
though often unclear and disputed.



*Idealism*. Content externalism is sometimes portrayed as a
thesis whose truth precludes idealism in at least some of its major
forms (see Rowlands 2003, for example). However, it is not clear that
this is really the case. For example, even a Berkeleian idealist could
accept Putnam's twin earth arguments if thus inclined. All that
is required for Putnam's argument to work is a distinction
between the way water and twater appear and their underlying
structures. This is something the Berkeleian idealist can, it seems,
accommodate. For example, the Berkeleian idealist can explain the
differences in underlying structure between water and twater in terms
of the difference in the ideas that God would flash into your mind and
that of your twin post 1750, when you both get down to the business of
investigating (what you think of as) the underlying structure of the
substance in your oceans and rivers. Content externalism requires a
reality that exists independently of the thinking subject or subjects
that feature in the thought experiment. But it does not appear to
require that this reality be non-mental. Some forms of content
externalism require this, supposition for example Sartre (1943
[1957]). But not all forms appear to do so. The relation between
content externalism and idealism, in its various forms, is, therefore,
not a straightforward one.



*Content Externalism and Self-Knowledge*. Externalism is
importantly connected with issues surrounding our introspective
knowledge of our own mental states. Such knowledge appears to be *a
priori*, or at least privileged, in that it is acquired without
relying on empirical evidence or observations. On the face of it,
externalism threatens the existence of such privileged knowledge. If
the contents of our thoughts are determined in part by our relations
to the environment, then one might think that external observations
are needed in order to know what we think. But self-knowledge does not
come about through empirical investigations. So either, contrary to
appearance, we do not really know the contents of our own thoughts or,
if we do, externalism is false. (See the entry on
 externalism and self-knowledge
 for further discussion).



*Externalism and Mind-Body Theories.* Externalism has important
consequences for a number of different mind-body theories. Burge
(1979) believes that externalism refutes individualistic theories of
intentional mental states. These are theories that define or explain
what it is for a person to have an intentional mental state purely in
terms of intrinsic facts about that person without reference to the
environment. Examples of such theories include the identity theory,
and
 functionalism (see entry)
 in its traditional guise. McGinn (1989) and Burge (1986, 1993) both
argue that externalism refutes the token-identity theory (and hence
the type-identity theory as well). This is contested by Davidson
(1987), Macdonald (1990) Gibbons (1993), and Frances (2007). With
regard to functionalism, one way to deal with externalism is to adopt
a divide-and-conquer strategy. One might restrict functionalism to
providing an account of what it is to be a particular kind of mental
state (e.g., a belief) individualistically, while adopting an
externalist theory of content (Fodor 1987). Alternatively, one might
adopt a "long arm" functionalism that specifies functional
roles in such a way that they incorporate worldly items and properties
(Block 1990). On such a view, the functional role of your belief that
water is wet would be different from the functional role of your
twin's belief that twater is wet, on the grounds that the
functional role of your belief involves you perceiving and doing
things with water whereas that of your twin involves her perceiving
and doing things with twater.



Though externalism may (or may not) be incompatible with these
internalist forms of physicalism, this should not be taken to imply
that externalism is itself an antiphysicalist doctrine, for one might
hold that although mental contents do not supervene on narrow physical
properties, they do supervene on wide physical properties. There is no
obvious reason for physicalism about the mind to require a
creature's mental properties to supervene on its narrow physical
properties. (For discussion of the requirements on physicalism, see
the entry on
 physicalism.)



*Mental Causation*. Another debate that arises out of
externalism concerns the legitimacy of wide contents in causal
explanations. Most philosophers agree with Davidson (1980) that
beliefs and desires play an important role in the causal explanation
of actions. However, it is not clear how this can be reconciled with
externalism. The problem comes up because it has been suggested that
causal explanations of behavior should appeal only to the intrinsic
properties of our bodies, properties that describe what is happening
here and now within us (Stich 1983). But externalism says that mental
contents are determined by causal, social or historical factors,
factors which extend spatially and temporally beyond the body. This
seems to imply that wide mental contents cannot be causally relevant
because of their relational nature.



There are two main strategies to show that wide mental contents can
legitimately enter into causal explanations. The first strategy is to
argue that the causal efficacy of a mental state with wide content
derives from the causal efficacy of a corresponding internal state. To
use a non-mental example, we often say that a mosquito bite causes
swelling, even though being a mosquito bite is a relational property.
However, one worry with this approach is why it doesn't show
that wide contents are not causally relevant after all, because it is
the internal component (the skin itching, swollen skin disturbance)
that is doing all the causal work. A different way to defend the
explanatory relevance of wide content is to identify its distinctive
explanatory role without them being parasitic upon the causal efficacy
of intrinsic properties. For example, according to Dretske (1988),
when my intention to drink water causes me to raise my glass, the
behavior that is the object of the causal explanation is not a single
event, but a complex process where an internal state causes some
bodily movement. Dretske argues that the wide content of my intention
plays a causal role because it provides a structural explanation of
how the internal brain state comes to be recruited to cause the bodily
movement. Williamson (2000) offers a different account of the
explanatory role of wide contents. He thinks they provide us with a
better understanding of the connection between the mental states of an
agent and his actions in the non-immediate future, because our actions
typically involve complex interactions with the environment. (For
further discussion, see the entry on
 mental causation).


## 5. Extended Mind



The expression *extended mind* was coined by Clark and Chalmers (1998), but essentially the same view has gone by a variety of names,
including "active externalism", "extended cognition" (both Clark and Chalmers 1998), "vehicle externalism" (Hurley 1998), "environmentalism" (Rowlands 1999),
and "cognitive integration" (Menary 2007). While this variegation in nomenclature is unimportant in itself, it is important
to (a) to distinguish extended mind from other views with which it might be confused, and (b) capture the significant internal variegation in views that might be classified as versions of extended mind. First, however, the general idea needs to be delineated (see Menary 2010 for a collection of thematic papers, both pro and con).



Mental content is not free-floating. Wherever there is mental content
there is something that has it--a *vehicle* of content.
Mental *states* (belief, desires, hopes, and fears, etc.) are
natural candidates for vehicles of content. So too are mental
*acts* (believing, desiring, hoping, fearing, etc.). As a
rough, initial approximation, *extended mind* is the view
that not all mental states or acts are exclusively located inside the
person who believes, desires, hopes, fears, and so on. Rather, some
mental states or acts are, in part, *constituted* by factors
(e.g., structures, processes) that are located outside the biological
boundaries of the individuals that have them. Thus, extended mind differs from content externalism not merely in being about mental vehicles rather than mental contents, but also in being committed to a claim of external location rather than simply external
individuation. If extended mind is true, some vehicles of
content are not, entirely, located inside the biological boundaries of
individuals that have them. Rather, they are, partly, constituted by,
or are composed of, factors that lie outside those boundaries. 



The distinction between states and acts is, in the context of this
form of externalism, a significant one, and the general idea of
extended mind can be developed in two quite different ways
depending on whether we think of the vehicles of content as states or
as acts. Thinking of the vehicles of content as states leads to a
*state-oriented* version of extended mind. Thinking of
these vehicles as acts leads to a *process-oriented*
alternative.


### 5.1 State-Oriented Extended Mind



Clark and Chalmers (1998) provide a canonical argument for
state-oriented extended mind. Otto is in the early stages of
Alzheimer's, and to facilitate his engagement with the world he
writes down what he suspects will be useful information in a notebook.
Reading in a newspaper that there is a particular exhibition going on
at the *Museum of Modern Art*, Otto looks in his notebook, and
finds the sentence, "The Museum of Modern Art is on
53rd Street", and, desiring to see the exhibition,
duly sets off to 53rd Street. Clark and Chalmers argue, or
are commonly taken to argue, that the sentence should be regarded as
one of Otto's beliefs. Their argument is predicated on a
*functionalist* conception of beliefs as individuated by their
functional roles. The sentence plays a functional role in Otto's
psychological economy that is, if not precisely identical, similar
enough to the functional role of a belief in the psychology of an
unimpaired subject for the sentence to qualify as a belief. If this is
correct, it means that at least one of Otto's beliefs lies in
the notebook rather than in his head. As usually understood, this view
qualifies as a form of state-oriented extended mind to the
extent that it identifies a mental state (a belief) with an external
structure (a sentence).


### 5.2 Objections to State-Oriented Extended Mind



The identification of a belief with a sentence has proved
controversial. One objection takes the form of an alleged *reductio
ad absurdum*: the identification of a belief with a sentence leads
to *cognitive bloat* (see Ludwig 2015). If the sentences in
Otto's notebook can qualify as his beliefs, why not the
sentences in an encyclopedia or the sentences found on the
internet--both of which Otto might also access with relative
ease? Clark and Chalmers responded to this worry via two stipulations:
(1) the subject must, at some time, have consciously endorsed this
information, and (2) the subject must have entered the information in
the book him- or herself. It is unclear whether these will work.
Subliminal beliefs provide a problem for the first stipulation, for
these are beliefs that have not been consciously endorsed by their
possessors. If such beliefs exist, then conscious endorsement of a
belief does not seem to be a necessary condition of its possession.
With regard to the second stipulation, it is not clear if this is
compatible with Clark and Chalmers's underlying functionalism.
According to functionalism, roughly, if something functions as belief
then it is a belief. From a functionalist perspective, how a belief
came to be acquired--entered into a person's collection of
beliefs--is not directly relevant. It would be relevant only if
it could be shown that having personally entered the belief into
one's collection of beliefs it essential to it having the
functional role of a belief. It is not clear what such an argument
would look like.



Another objection to state-oriented extended mind is that it
confuses the claim that vehicles of cognition are extended with the
(weaker) claim that they are *embedded* or *scaffolded*
or, equivalently, that it falls victim to a
*coupling-constitution* confusion (Adams & Aizawa 2001,
2008; Rupert 2004). On the state-oriented interpretation, a vehicle of
content is extended if it is *identical* with, or constituted
by, a structure that lies outside the biological boundaries of an
individual. But a vehicle of cognition is (merely) *embedded*
if it depends on, or is coupled with (causally or otherwise)
structures that lie outside the biological boundaries of the
individual without being identical with those structures. According to
this second objection, arguments for extended mind only
establish that vehicles of content are embedded, or coupled, with the
environment rather than being extended or constituted, by the
environment.



A third type of objection to state-oriented extended mind is the
*original intentionality* objection, versions of which have
been leveled by Adams and Aizawa (2001, 2008), Fodor (2009), and
Rowlands (2010). In a tradition instigated by Brentano, original
intentionality is often taken to be the hallmark of the mental.
Original intentionality is defined as intentionality that is not
derived. And derived intentionality is intentionality that derives
from the mental activity, often mediated by social conventions, of a
subject. The intentionality of the sentence, "The Museum of
Modern Art is on 53rd Street", is clearly derived
intentionality. In itself, this sentence is merely a pattern of shapes
against a contrastive background and, in principle, could mean
anything. To mean something, it must be interpreted, and its
intentionality is, therefore, derived. Beliefs are mental entities. If
original intentionality is the hallmark of the mental, then the
sentence in Otto's notebook is not mental. Therefore, the
objection runs, it is difficult to see how it could be a belief.


### 5.3 Process-Oriented Extended Mind



State-oriented extended mind identifies a mental state (e.g., a
belief) with an external structure (e.g., a sentence). However, mental
states are not the only candidates for the vehicles of content. Mental
acts--thinking, believing (or judging), remembering,
etc.--have at least as much claim to be regarded as such
vehicles. And switching the focus from states to acts affords the
possibility of a more process-oriented interpretation of extended mind. We might regard Otto's notebook as an item of scaffolding in roughly the sense championed by Vygotsky (1934 [1962]). In these terms, the state-oriented version of extended mind identifies a mental state with a piece of this scaffolding--if this piece plays the requisite functional role. In the process-oriented version of extended mind, focus switches from the scaffolding to the process of manipulating the scaffolding. This manipulating of the scaffolding can, on the process-oriented version of extended mind, form part of a cognitive process.



The process-oriented version of extended mind would interpret
the case of Otto rather differently. There is no identification of a
mental state with an external structure--a belief with a
sentence. Rather, there is, first of all, a mental process. Describing
this as a process of believing is, perhaps, a little forced: a process
of remembering seems more apt. When Otto engages with, or
*manipulates*, his notebook--flipping through the pages,
and scanning each page--this manipulation forms part of his
process of remembering the location of the Museum of Modern Art. This
is only part of the process, of course: little remembering would get
done without a suitable contribution from the brain. Nevertheless,
Otto's manipulation of the book is part of that process.



Two distinct types of motivation can be identified for this claim. The
first is a broadly functionalist one, akin to the functionalist
motivation for state-oriented extended mind. The idea is that
the computational profile of the process of manipulating the book is
broadly similar to that of internal processes responsible for
cognition (Wilson 1994, 2004; Clark 1989, 1997, 2008a, 2008b; Rowlands 1999, 2010, Wheeler
2010). Standard accounts of cognition postulate information-bearing structures (roughly, representations) and transformative processes performed on those structures, where these processes have the function of identifying information and making it available either to the cognitive subject or to further processing operations. Thus, for example, David Marr's canonical account of vision postulates a series of information-bearing structures--retinal image, raw primal sketch, full primal sketch, and so on, combined with operations that successively transform one structure into the next. The overall function of these processes is to identify and make available to the subject information that can be used to solve the task of seeing an object. Similarly, when Otto manipulates his notebook this, in general terms, is also what he seems to be doing: acting on information-bearing structures with a view to making available information that he needs to solve the cognitive task of remembering the location of The Museum of Modern Art. From this suitably abstract computational perspective, it is argued, there does not seem to be a huge amount of difference between internal processes performed by the brain on information-bearing structures and external processes performed by the organism on information-bearing structures. They have
the same abstract computational profile and purpose.



Another type of argument draws its inspiration from the
phenomenological tradition. Wheeler (2005), for example, draws on the
work of Heidegger (1927 [1962]) in defending a version of extended mind. Rowlands (2010), developing certain themes implicit in
Husserl and Sartre, defends a model of intentionality as *revealing
activity*: the presenting (revealing or disclosing) of an object
as falling under a given mode of presentation. While the activity
through which this presentation occurs can be purely
internal--i.e., neural or neurocomputational activity--it
need not be, and typically is not. Often this internal activity is
combined with actions performed by an organism on the world around it.
On this view, when Otto manipulates his book, he is engaging in
revealing activity: The Museum of Modern Art is revealed, disclosed or
presented as being located on East 53rd Street. This
revealing activity comprises both activity occurring in Otto's
brain and wider activity performed by Otto on the world. As revealing
activity, therefore, the process of remembering occurs partly inside
Otto and partly outside him.



Whether computationally or phenomenologically inspired,
process-oriented extended mind *may* fare better with
the objections that were leveled at its state-oriented counterpart.
The bloat objection seems to have less purchase on process-oriented
extended mind. For example, Otto's act of remembering
extends no further than the things he does to and with his notebook.
There is no reason for thinking that it extends into things such an
encyclopedia or the internet that Otto is not currently manipulating
or exploiting.



The original intentionality objection is also, at least partly,
deflected. In this amalgamated process, that combines things going on
both inside and outside Otto's skin, there is original
intentionality aplenty. Otto has to read what he scans on each page,
and his seeing will have original intentionality. He will have to
understand what he sees, and this understanding will also have
original intentionality. Therefore, the overall process is not at all
devoid of original intentionality (Menary 2006, 2007). It can,
however, can be objected that this original intentionality is confined
to segments of the process that are located exclusively inside
Otto's skin (Adams 2010). A response to this objection might
take two forms. One is to accept the claim, and argue that it does not
matter. In this vein, one might point to that the fact that it would
be extremely implausible to require that every internal part of a
cognitive process, understood neuro-physiologically or
computationally, must possess original intentionality. A retinal
image, for example, might possess original intentionality of a sort.
The visual representation into which this image is progressively
transformed by constructive operations on the part of the brain would,
probably, possess original intentionality. But those constructive
operations would not (Rowlands 2010). The other option is to deny the
claim. This would require showing that at least some things that are
not located in or at the skin possess original intentionality.
Rowlands (2006), for example, argues that this is true of what he
calls *pre-intentional actions* or *doings*. The debate
is ongoing, and it is not clear whether there is an answer that would
convince both parties.


### 5.4 The Mark of the Cognitive/Mental



Tied to this lack of definitiveness is the third charge leveled
against extended mind: the coupling-constitution confusion. A
simple charge of confusion is difficult to sustain. Proponents of
extended mind are, in general well aware of the distinction
between causal coupling and constitution. In the case of Otto, for
example, Clark and Chalmers argue that a sentence should be identified
with a belief--rather than the latter being merely coupled with
the former--precisely because the sentence has the functional
role of a belief. A more plausible form of the objection might be that
the arguments provided by proponents of extended mind--whether state- or process-oriented--do not
establish what these proponents have taken them to
establish. Specifically, they do not establish anything more than the
claim that cognitive processes are coupled with external processes
rather than that they are constituted by them. Answering both the
original intentionality objection and the coupling-constitution
objection, therefore, seems to require the ability to identity when a
process is, and is not, a cognitive process.



Rupert (2009) argues that the best way to approach this is through the
identification of a cognitive system, an identification that will rest
heavily on how the sciences of the mind individuate such systems. The
most plausible conception of a cognitive system, he argues, counts
against extended mind. Another approach argues the need for
identification of a *mark of the cognitive*--a set of
necessary, sufficient, or necessary and sufficient, conditions for a
process to count as cognitive. Reaction to this suggestion can be
divided into three broad camps. First, there are those who think that
a mark of the cognitive is not necessary. Just as we can study biology
without a mark of the biological, and practice medicine without a
criterion of the medical, we can also do cognitive science without a
criterion of the cognitive (Allen 2017). Second, there are those who
think a criterion of cognition is required, can be identified, and
counts against extended mind (Adams 2010). Third, there are
those who think a criterion of the cognitive is available and it
supports extended mind (Rowlands 2009, 2010).


## 6. The Scope of Extended Mind



In its earlier incarnations, the scope of extended mind was
relatively restricted, it being understood, primarily, as a thesis
about cognition. The types of external structure or activity involved
in developing the idea of extended mind reflected this focus on
cognition. They were predominantly thought of as structures that
carried information pertinent to the solution of cognitive tasks that
an organism might face, where the organism, through acting on these
structures, could transform this information from information merely
present in the structures to information that is available to the
organism (Rowlands 2010). Accordingly, expansion in the scope of
extended mind can, and has, occurred along two (related)
dimensions: (1) expansion in scope from cognition to other kinds of
mental process, and (2) expansion in the types of external structure
involve in these extended mental processes.



Some prominent advocates of extended cognitive states or processes
have been skeptical of the idea that consciousness could be extended,
often on the grounds that external structures do not possess the kind
of informational bandwidth necessary to sustain conscious experience
(Clark 2009, Chalmers 2019). Others are more sanguine about this
possibility, and extended accounts of experiences (Rowlands 2010) and
other conscious states, such as emotions (Krueger 2014; Krueger &
Szanto 2016; Carter et al. 2016) have been defended. At the same time,
and relatedly, there has been an expansion in the types of external
structures thought relevant. In particular, there has been a
pronounced *social turn* in extended mind in recent
years, exploring the ways in which social structures and institutions
might also, in part, be constitutive of constitute mental processes
(De Jaegher et al. 2010, Gallagher 2013, Lyre 2018, and Slors 2019),
and the idea that our basic biological cognitive faculties may be
transformed by a process of *enculturation* (Menary 2015) has
helped reshape extended mind in recent years. One important
example of this social turn pertains to the study of memory, in
particular, in the way in which memory is often
*transactive*--involving the combined efforts of two or
more people, bonded together as a coupled system (Barnier et al 
2008; Sutton 2008, 2010, 2015).


## 7. Extended Mind and the 4E Mind



Another way of delineating the scope of extended mind is by more
precisely identifying its location in an array of anti-Cartesian
possibilities. Extended mind supplies one of the
"E"s in what has become known as *4E cognition*, or
the *4E mind* more generally in deference to the idea that its
scope may be broader than simply cognition (Newen, De Bruin, &
Gallagher 2018). The label "4E" is intended to capture the
idea that at least some mental processes are *embodied*,
*embedded*, *enacted* and/or *extended*, or some
combination thereof.



The clam that mental processes are *embodied* can mean at least
two distinct things (Prinz 2009). On the one hand, it can signify that
mental processes depend on possession and use of a body rather than
merely a brain (Haugeland 1993, Shapiro 2004). This idea can, itself,
fragment into different views, depending on how we understand the idea
of dependence. The claim can be understood as causal dependence:
(some) mental processes causally depend (for their existence,
identity, etc.) on the body and its characteristics. On the other
hand, it can be understood as a claim of *constitution*: (some)
processes occurring inside the body, but outside the brain, can
partially constitute mental processes. On the other hand, there is
another way of understanding the claim that mental processes are
embodied, specifically, as the claim that (some) mental processes
depend on mental representations that relate to body (Prinz 2009).
These representations come in two forms: ones that affect the body,
such as motor commands, and ones that represent or respond to the
body, such as a perception of a bodily movement. Thus, on this view, a
mental process would count as embodied if it involves, for example, a
representation located in the motor cortex, even though the motor
cortex is intracranial.



Some proponents of extended mind regard their view as
antithetical to the claim that mental processes are embodied. For
example, Clark (2008a) argues that there is, at the very least, a tension between the two views. His version of extended mind is grounded in a liberal version of
functionalism, according to which mental states and processes are individuated by functional roles specified in a fairly abstract way, as general principles linking perception, mental states and processes, and action that does not specify, in any depth, the nature of the mechanisms responsible for this linkage. The claim of embodiment, on
the other hand, Clark sees as grounded either in a rejection of functionalism, or in a form of functionalism that is far more chauvinistic, in that it does, in its specification of functional roles, specify at least some of the details of their realizing mechanisms. Others see extended and embodied views of the mind as much more compatible or aligned than this, even as different facets of the same view (for example, Menary 2007, Rowlands 2010).



A mental process is *embedded* if it functions, perhaps has
been designed to function, in tandem with a surrounding, environmental
scaffolding, such that without the presence of this scaffolding the
process will fail to do what it is supposed to do, or be less likely
to achieve what it is supposed to achieve, or do what it is supposed
to so in a less than maximally efficient way, etc. The external
scaffolding carries information pertinent to the cognitive task that
the process is designed to accomplish, and a cognizing organism can,
by manipulating or exploiting the structure in an appropriate way,
avail itself of this information. Cognition, on this view, still
resides in the head. But the net result is that at least some of the
difficulty of the cognitive task is offloaded onto the world. The
required internal, intra-cranial, processing is not as sophisticated
as it would have needed to be if there was no environmental
scaffolding around. Think of the difference between doing long
division in your head or doing it with a pen and paper (Rumelhart et
al. 1986). The external notation is a form of scaffolding that reduces
the complexity of the required internal processing. Kirsh and Maglio
(1994) label this kind of action--that changes the nature of the
cognitive task that must be performed internally--*epistemic
action*.



The claim that some mental processes are embedded is, prima facie, one
that belongs on a spectrum of anti-Cartesian ways of conceptualizing
the mind. A, perhaps, curious feature of the recent dialectic, however, is
that the idea of embedding is often used as a way of devaluing the
claims of extended mind. The idea, here, is that the arguments
purported to establish that mental processes are extended really only
show that such processes are embedded (Adams & Aizawa 2008, Rupert
2004). This objection is a version of the
*coupling-constitution* objection outlined in
 section 5.2.



A mental process is *enacted* if it involves, or is constituted
by, a dynamic, interactive coupling of processes occurring inside the
skin or skull of an organism and processes external to said skin or
skull. Enactivism appears in a variety of forms. However, it is
plausible to suppose that process-oriented extended mind
coincides with at least some of them. In explaining the nature of
conscious experience, for example, many forms of enactivism appeal to
the ability of the experiencing organism to act on the world around.
Abilities, perhaps, need not be extended. But some versions of
enactivism also appeal to the *exercise* of these abilities. A
common enactivist way of explaining the sense of phenomenal
presence--the sense of being presented with a richly structured,
detailed world--does not appeal to a representational structure
that replicates this detail. If representations area involved at all,
they give us merely the rough gist of the visual situation. The sense
of richness and details results from the experiencing organism
availing itself of the richness and detail in the world itself
(O'Regan & Noe 2001, Noe [ed.] 2002, Noe
2004). By acting on a rich and detailed world, therefore, the organism
injects richness and detail into its experience. The organism's
experience of the richness and detail of the world is realized not by
a representation but by a sequence of dynamic, coupled interactions
with the external scene itself.



Enactivism comes in a variety of forms (Chemero 2009; Hutto & Myin
2012, 2017; Noe 2004). But an emphasis on dynamic, tightly
coupled interactions between organism runs through all versions of
enactivism and finds clear echoes in at least the process-oriented
version of extended mind. Thus, while there are, perhaps,
differences of emphasis, it is likely that some versions of enactivism
coincide with some versions of extended mind.