David Chalmers - Collection Of Papers Concerning Consciousness

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Online papers on consciousness
Online papers on consciousness 
Compiled by David Chalmers 
This is a directory of 1123 online papers on consciousness and related topics. Suggestions for addition 
are welcome. Most papers are by academic philosophers or scientists. 
I have now divided this page into three separate pages, as follows: 
l Part I: Philosophy of Consciousness [368 papers]
l Part II: Other Philosophy of Mind [433 papers] 
l Part III: Science of Consciousness [322 papers]
TABLE OF CONTENTS
I. PHILOSOPHY OF CONSCIOUSNESS 
l The concept of consciousness
l The explanatory gap
l Materialism and dualism
l The knowledge argument
l Materialism and modality
l Metaphysics of consciousness
l Panpsychism
l Zombies
l Qualia 
l The contents of consciousness 
l Representationalism 
l Consciousness as higher-order thought 
l Introspection, self-knowledge, and self-consciousness 
l The unity of consciousness 
l The function of consciousness 
l Philosophy of consciousness (misc.) 
II. OTHER PHILOSOPHY OF MIND 
l Language and thought 
l Propositional attitudes 
l Theories of content 
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Online papers on consciousness
l Internalism and externalism 
l Concepts 
l Mental content (misc.) 
l Folk psychology 
l Metaphysics of mind 
l The self and personal identity 
l Free will 
l Philosophy of mind (misc.) 
l The Chinese Room 
l Godel's theorem and AI 
l The Turing test 
l Philosophy of connectionism 
l Philosophy of AI (misc.) 
III. SCIENCE OF CONSCIOUSNESS 
l Neuroscience of visual consciousness 
l Consciousness and neuroscience 
l Cognitive models of consciousness 
l Unconscious perception 
l Implicit memory 
l Implicit learning 
l Change blindness and inattentional blindness 
l Visual consciousness (misc.) 
l Consciousness and psychology (misc.) 
l Consciousness in the history of psychology 
l Animal consciousness 
l Consciousness and artificial intelligence 
l Consciousness and physics 
l Phenomenology 
l Miscellaneous 
For other sources of online papers, and for bibliographies of around 2000 offline papers on 
consciousness, see: 
l people with online papers in philosophy 
l web resources related to consciousness, philosophy, and such 
l directory of online philosophy papers (Joe Lau)
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Papers on Consciousness (David Chalmers)
Papers on Consciousness (David Chalmers).
This page contains pointers to some papers on consciousness. The papers here should be accessible to 
people without a background in philosophy. Philosophers might be interested in the more technical 
papers under papers on mind, modality, and meaning. A separate page has information on my book The 
Conscious Mind. Most items are in HTML, with a Postscript version also available in some cases. The 
papers fall into a few distinct categories.
The Problems of Consciousness
Consciousness and its Place in Nature
This is a new overview paper on the the metaphysics of consciousness. It summarizes arguments against 
materialism, and uses these to give a detailed taxonomy of reductive and nonreductive views (three 
each). It covers some of the same ground as the first two papers below (although it's oriented more 
toward metaphysics than toward science), while also covering some of the more technical material in my 
book and some new things. It will appear in the forthcoming Blackwell Guide to Philosophy of Mind, 
edited by Stephen Stich and Fritz Warfield.
Facing Up to the Problem of Consciousness (PS)
This paper gives a nontechnical overview of the problems of consciousness and my approach to them. In 
it I distinguish between the easy problems and the hard problem of consciousness, and argue that the hard 
problem eludes conventional methods of explanation. I argue that we need a new form of nonreductive 
explanation, and make some moves toward a detailed nonreductive theory. This paper, based on a talk I 
gave at the 1994 Tucson conference on consciousness, appeared in a special issue of the Journal of 
Consciousness Studies in 1995, and also in the 1996 collection Toward a Science of Consciousness, 
edited by Hameroff, Kaszniak, and Scott (MIT Press, 1996).
Moving Forward on the Problem of Consciousness
After "Facing Up..." was published, about 25 articles commenting on it or on other aspects of the "hard 
problem" appeared in JCS (links to some of these papers are contained in the article). My (lengthy) reply, 
"Moving Forward...", appeared in JCS vol. 4, pp. 3-46, 1997. All the papers and my reply have been 
collected in the book, Explaining Consciousness: The Hard Problem (edited by Jonathan Shear), 
published by MIT Press in July 1997.
The Puzzle of Conscious Experience
This paper appeared in Scientific American in December 1995. It is essentially an even less technical 
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Papers on Consciousness (David Chalmers)
version of the first article above, with some pretty pictures. As with most Scientific American articles, 
much of this article was heavily revised by the editors, and there are a few passages that I cringe at. But 
it's not a bad introduction.
Consciousness and Cognition (PS)
This is an older paper on consciousness, written when I was a graduate student at Indiana. It talks about 
the odd fact that even if consciousness is not reductively explainable, our claims about consciousness 
should be, and discusses various ways in which this tension might be resolved, eventually proposing a 
proto-theory of consciousness based on the notions of pattern and information. I no longer agree with 
everything in this paper, and it gets a bit wild toward the end, but it covers some interesting issues. I've 
never tried to publish it, but for some reason it is still my favorite among the papers I've written on the 
subject.
The Science of Consciousness
On the Search for the Neural Correlate of Consciousness
This is a constructive analysis of the search for the "neural correlate of consciousness" (or the NCC, as 
it's sometimes called). I argue that because we don't have any way of detecting consciousness directly 
(i.e., we have no "consciousness meter"), the search is driven by pre-empirical bridging principles 
instead. I discuss some of these principles and draw some conclusions about the shape of the search. This 
paper is largely a transcript of my talk at the 1996 Tucson conference on consciousness, although some 
fun and games have been omitted (here are some visuals from the talk). It was published in Toward a 
Science of Consciousness II, edited by Hameroff, Kaszniak, and Scott (MIT Press, 1998).
What is a Neural Correlate of Consciousness?
This more recent and longer paper deals with some different aspects of the NCC issue, with reference to 
recent empirical work in the field (e.g. work in visual neuroscience by Logothetis, Milner and Goodale, 
and others). In particular it addresses what it means to be a neural correlate of consciousness, 
distinguishes different sorts of NCCs, and discusses the methodology of the search. It raises some 
questions about the conclusions that can be drawn from lesion studies. This paper was given at the 1998 
ASSC conference on Neural Correlates of Consciousness, and appeared in Neural Correlates of 
Consciousness: Conceptual and Empirical Questions, edited by Thomas Metzinger (MIT Press, 2000). 
First-Person Methods in the Science of Consciousness
In this short paper I argue that the task of a science of consciousness is to connect third-persondata about 
brain and behavior to first-person data about conscious experience, and I discuss the difficult question of 
how we might investigate and represent first-person data. I also discuss some specific issues about 
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Papers on Consciousness (David Chalmers)
emotion. This paper was written for a Tucson online workshop on emotion and consciousness, and 
appeared in the Fall 1999 Consciousness Bulletin from the Center for Consciousness Studies. 
Commentaries and Reviews
Insentience, Indexicality, and Intensions
This is a commentary on John Perry's book Knowledge, Possibility, and Consciousness (MIT Press, 
2001), which defends a materialist view against a number of arguments (the zombie argument, the 
knowledge argument, the modal argument), and addresses the discussion in my book. The commentary 
will appear in a symposium on Perry's book in Philosophy and Phenomenological Research
Availability: The Cognitive Basis of Experience?
Here I argue that the cognitive correlate of conscious experience is direct availability for global control, 
and use this to shed light on a few vexing questions. This was written as a commentary on Ned Block's 
paper "On A Confusion about a Function of Consciousness", and appeared in Behavioral and Brain 
Sciences and also in the collection The Nature of Consciousness: Philosophical Debates from MIT Press, 
edited by Block, Flanagan, and Guzeldere. This paper overlaps to some extent with "On the search for a 
neural correlate of consciousness". 
Self-Ascription Without Qualia: A Case-Study
This is a commentary on Alvin Goldman's piece "The Psychology of Folk Psychology", in Behavioral 
and Brain Sciences (June 1993). The paper contains a zombie thought-experiment or two, for people who 
like that sort of thing.
Review of Journal of Consciousness Studies
This is a review of the first issue of the Journal of Consciousness Studies. It appeared in the Times 
Literary Supplement in November 1994.
Miscellaneous
Absent Qualia, Fading Qualia, Dancing Qualia (PS)
In this paper I use thought-experiments to argue that functional organization fully determines conscious 
experience. These thought-experiments involve the gradual replacement of neurons by silicon chips, and 
similar scenarios. I argue that if "absent qualia" or "inverted qualia" are possible, then phenomena I call 
"fading qualia" and "dancing qualia" will be possible; but I argue that it is very implausible that fading or 
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Papers on Consciousness (David Chalmers)
dancing qualia are possible. The resulting position is a sort of "nonreductive functionalism". This paper 
appears in the collection Conscious Experience from Ferdinand Schöningh (1995), edited by Thomas 
Metzinger. (There is also a German version entitled "Fehlende Qualia, schwindende Qualia, tanzende 
Qualia" (!), but it is not available on the net.)
What is the Unity of Consciousness?
This paper is co-authored with Tim Bayne. We distinguish a number of different senses in which it might 
be said that a subject's conscious experiences are unified, and isolate a central notion for which the claim 
that consciousness is necessarily unified is tenable without being trivial. We then discuss potential 
counterexamples to this unity thesis, and will consider the implications of the unity thesis for theories of 
consciousness more generally. This paper is coming out in The Unity of Consciousness: Binding, 
Integration, Dissociation from Oxford University Press, edited by Axel Cleeremans.
Go to:
l David Chalmers' home page
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Papers on Mind, Modality, and Meaning (David Chalmers)
Papers on Mind, Modality, and Meaning (David 
Chalmers).
This page contains some papers around the borders of the philosophy of mind and language, 
metaphysics, and epistemology. These papers (except "The Extended Mind") mostly presuppose 
significant philosophical background (non-philosophers might prefer my page of less technical papers on 
consciousness). The papers mostly deal with interwoven issues concerning meaning and modality, 
sometimes against a background of issues in the philosophy of mind. There is some overlap between the 
papers, as related issues are approached from different angles. Much of this is being cannibalized for a 
book manuscript currently in progress (working title: On What Might Be).
On Sense and Intension
Over the last few years I have been working on an account of meaning and of possibility on which these 
notions are closely tied to reason and cognition. The central tool in doing this has been a two-
dimensional semantic framework (invoked in many of the papers on this page). This paper serves as an 
introduction to those ideas, motivated by the defense of a Fregean conception of meaning. In the paper, I 
articulate some Fregean theses about sense, develop an intensional account of sense on which it is 
constitutively connected to epistemic possibility, and use this account to deal with various objections to 
Fregean views. Along the way, the two-dimensional framework as I understand it emerges.
The Nature of Epistemic Space.
This unpublished paper takes a more foundational approach to some of these issues, grounding some of 
the key ideas in a notion of epistemic possibility, and an epistemic space made up of maximal epistemic 
possibilities, or "scenarios". I explore various ways of constructing the space of scenarios -- one tied to 
centered possible worlds, and one tied directly to epistemic notions. And I outline some applications of 
the framework from this perspective: e.g. to Fregean sense, narrow content, indicative conditionals, and 
hyperintensionality.
The Foundations of Two-Dimensional Semantics
This monster paper (written for the Barcelona conference on two-dimensionalism) is a sort of "compare-
and-contrast" on the various versions of two-dimensional semantics. It starts by motivating this sort of 
framework, and then discusses in detail the two main sorts of available understandings of the framework: 
contextual and epistemic understandings. I argue that contextual understandings (e.g. that of Stalnaker) 
can't do the work that is required, but that an epistemic uderstanding can. I set out my own understanding 
in detail, and then locate existing versions of the framework in the conceptual space as set out.
The Components of Content 
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Papers on Mind, Modality, and Meaning (David Chalmers)
This paper tries to do for thought what first paper above does for language: give an account of the 
contents of thought on which content is closely tied to reason and cognition. I decompose content into 
epistemic and subjunctive content, both of which are truth-conditional. Epistemic content is generally 
internal to a cognitive system, and governs rational relations between thoughts, so it can play the role of 
"narrow" or "cognitive" content. I apply this framework to a number of puzzles (Frege's puzzle, Kripke's 
puzzle, the problem of the essential indexical, the mode-of-presentation problem, etc.) in the philosophy 
of mind and the philosophy of language. The unpublished 1995 version of this paper has been fairly 
widely cited. The new revised version is finally to be published in my anthology Philosophy of Mind: 
Classical and Contemporary Readings in 2002.
Does Conceivability Entail Possibility?
This paper addresses the epistemology of modality, and argues for a sort of modal rationalism (a priori 
access to modality). It distinguishes a number of of sorts of conceivability, and with these distinctions in 
hand argues that certainsorts of conceivability plausibly entail sorts of possibility. The second half of the 
paper addresses potential gaps between the two, and gives a positive argument for modal rationalism. 
Lots of interesting issues come up along the way. This paper is forthcoming in Conceivability and 
Possibility, edited by Tamar Gendler and John Hawthorne (Oxford, 2002).
Conceptual Analysis and Reductive Explanation
This paper, co-authored with Frank Jackson, is a reply to Ned Block and Robert Stalnaker's paper 
"Conceptual Analysis, Dualism, and the Explanatory Gap". It doesn't presuppose knowledge of that 
paper. It defends from first principles the thesis that there is an a priori entailment from microphysical 
and phenomenal truths (plus or minus a bit) to macroscopic truths; it addresses Block and Stalnaker's 
objections to this thesis; and finally argues that a priori entailment is required for reductive explanation 
and for physicalism. The paper appears in Philosophical Review 110:315-61, 2001.
Materialism and the Metaphysics of Modality
This paper was my response in a symposium on my book The Conscious Mind in Philosophy and 
Phenomenological Research in June 1999 (the corresponding precis of the book is also online). The 
commentators were Sydney Shoemaker, Brian Loar, Chris Hill & Brian McLaughin, and Stephen Yablo, 
all of whom take a "type-B materialist" position on which there is an epistemic gap between physical and 
phenomenal, but no modal gap. This gets quickly into issues about the 2-D analysis of a posteriori 
necessity, and whether there are "strong necessities" that escape it. I argue that there are not, and argue 
for a sort of modal rationalism.
Mind and Modality
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Papers on Mind, Modality, and Meaning (David Chalmers)
This material (in detailed outline form) corresponds to a series of three lectures I gave at Princeton 
University in October 1998. The second and third largely contain material since written up in the papers 
on this page on conceivability and on phenomenal belief. The first lecture contains some material not 
contained elsewhere.
The Content and Epistemology of Phenomenal Belief
This long paper has two halves. The first half gives an account of phenomenal concepts and phenomenal 
beliefs, on which their content is partly constituted by the quality of an experience. The second half 
applies this account to epistemological issues: e.g. arguing for a limited incorrigibility thesis, defending a 
sort of foundationalism about phenomenal knowledge, defending the phenomenal realist from certain 
epistemological problems, and addressing the "Myth of the Given". The paper is forthcoming in 
Consciousness: New Philosophical Essays, edited by Quentin Smith and Alexandr Jokic (Oxford, 2002).
The Tyranny of the Subjunctive
This is just an extended outline at the moment. I argues for a parallel between indicative and subjunctive 
conditionals, on the one hand, and the two dimensions of possibility in the 2-D framework. The standard 
contemporary analysis of possibility and necessity is grounded in subjunctive conditionals. I suggests 
that this is entirely arbitrary, and has had a distorting effect on many areas of philosophy.
The Extended Mind 
This paper (jointly written with Andy Clark) argues that cognitive states are not necessarily "in the head", 
for reasons quite independent of the reference-based considerations of Putnam and Burge. Instead, we 
advocate an "active externalism", focusing on situations in which an organism is coupled with their 
environment into what is effectively a single cognitive system (as with a person who relies on a notebook 
as memory, for example). We argue in detail that mental states such as beliefs can be externally 
constituted in this way. This leads to a reconception of the relation between mind and world. 
(Reconciling the externalism of this paper with the internalism of "The Components of Content" is left as 
an exercise for the reader.) This paper was published in Analysis 58:10-23, 1998, and was reprinted in 
The Philosopher's Annual, 1998. Here is a commentary. 
Is There Synonymy in Ockham's Mental Language?
This is my sole venture into the history of philosophy so far. It was written when I was a graduate student 
in Paul Spade's medieval logic class at Indiana. William of Ockham held that we think in a "mental 
language", not unlike the language of thought that some contemporary philosophers believe in. The 
question arises whether the mental language can contain synonyms, or whether these are just artifacts of 
ordinary language. Most people have said no. Here I give some reasons to say yes. This paper is 
published in The Cambridge Companion to Ockham, edited by Spade, published by Cambridge 
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The Extended Mind
The Extended Mind
Andy Clark & David J. Chalmers [*]
Department of Philosophy
Washington University
St. Louis, MO 63130
Department of Philosophy
University of Arizona
Tucson, AZ 85721
andy@twinearth.wustl.edu
chalmers@arizona.edu
*[[Authors are listed in order of degree of belief in the central thesis.]] 
[[Published in Analysis 58:10-23, 1998. Reprinted in (P. Grim, ed) The Philosopher's Annual, vol XXI, 1998.]] 
1 Introduction
Where does the mind stop and the rest of the world begin? The question invites two standard replies. 
Some accept the demarcations of skin and skull, and say that what is outside the body is outside the 
mind. Others are impressed by arguments suggesting that the meaning of our words "just ain't in the 
head", and hold that this externalism about meaning carries over into an externalism about mind. We 
propose to pursue a third position. We advocate a very different sort of externalism: an active 
externalism, based on the active role of the environment in driving cognitive processes. 
2 Extended Cognition
Consider three cases of human problem-solving: 
(1) A person sits in front of a computer screen which displays images of various two-dimensional 
geometric shapes and is asked to answer questions concerning the potential fit of such shapes into 
depicted "sockets". To assess fit, the person must mentally rotate the shapes to align them with the 
sockets. 
(2) A person sits in front of a similar computer screen, but this time can choose either to physically rotate 
the image on the screen, by pressing a rotate button, or to mentally rotate the image as before. We can 
also suppose, not unrealistically, that some speed advantage accrues to the physical rotation operation. 
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(3) Sometime in the cyberpunk future, a person sits in front of a similar computer screen. This agent, 
however, has the benefit of a neural implant which can perform the rotation operation as fast as the 
computer in the previous example. The agent must still choose which internal resource to use (the 
implant or the good old fashioned mental rotation), as each resource makes different demands on 
attention and other concurrent brain activity. 
How much cognition is present in these cases? We suggest that all three cases are similar. Case (3) with 
the neural implant seems clearly to be on a par with case (1). And case (2) with the rotation button 
displays the same sort of computational structure as case (3), although it is distributed across agent and 
computer instead of internalized within the agent. If the rotation in case (3) is cognitive, by what right do 
we count case (2) as fundamentally different? We cannot simply point to the skin/skull boundary as 
justification, since the legitimacy of that boundary is precisely what is at issue. But nothing else seems 
different. 
The kind of casejust described is by no means as exotic as it may at first appear. It is not just the 
presence of advanced external computing resources which raises the issue, but rather the general 
tendency of human reasoners to lean heavily on environmental supports. Thus consider the use of pen 
and paper to perform long multiplication (McClelland et al 1986, Clark 1989), the use of physical re-
arrangements of letter tiles to prompt word recall in Scrabble (Kirsh 1995), the use of instruments such as 
the nautical slide rule (Hutchins 1995), and the general paraphernalia of language, books, diagrams, and 
culture. In all these cases the individual brain performs some operations, while others are delegated to 
manipulations of external media. Had our brains been different, this distribution of tasks would doubtless 
have varied. 
In fact, even the mental rotation cases described in scenarios (1) and (2) are real. The cases reflect 
options available to players of the computer game Tetris. In Tetris, falling geometric shapes must be 
rapidly directed into an appropriate slot in an emerging structure. A rotation button can be used. David 
Kirsh and Paul Maglio (1994) calculate that the physical rotation of a shape through 90 degrees takes 
about 100 milliseconds, plus about 200 milliseconds to select the button. To achieve the same result by 
mental rotation takes about 1000 milliseconds. Kirsh and Maglio go on to present compelling evidence 
that physical rotation is used not just to position a shape ready to fit a slot, but often to help determine 
whether the shape and the slot are compatible. The latter use constitutes a case of what Kirsh and Maglio 
call an `epistemic action'. Epistemic actions alter the world so as to aid and augment cognitive processes 
such as recognition and search. Merely pragmatic actions, by contrast, alter the world because some 
physical change is desirable for its own sake (e.g., putting cement into a hole in a dam). 
Epistemic action, we suggest, demands spread of epistemic credit. If, as we confront some task, a part of 
the world functions as a process which, were it done in the head, we would have no hesitation in 
recognizing as part of the cognitive process, then that part of the world is (so we claim) part of the 
cognitive process. Cognitive processes ain't (all) in the head! 
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The Extended Mind
3 Active Externalism
In these cases, the human organism is linked with an external entity in a two-way interaction, creating a 
coupled system that can be seen as a cognitive system in its own right. All the components in the system 
play an active causal role, and they jointly govern behavior in the same sort of way that cognition usually 
does. If we remove the external component the system's behavioral competence will drop, just as it 
would if we removed part of its brain. Our thesis is that this sort of coupled process counts equally well 
as a cognitive process, whether or not it is wholly in the head. 
This externalism differs greatly from standard variety advocated by Putnam (1975) and Burge (1979). 
When I believe that water is wet and my twin believes that twin water is wet, the external features 
responsible for the difference in our beliefs are distal and historical, at the other end of a lengthy causal 
chain. Features of the present are not relevant: if I happen to be surrounded by XYZ right now (maybe I 
have teleported to Twin Earth), my beliefs still concern standard water, because of my history. In these 
cases, the relevant external features are passive. Because of their distal nature, they play no role in 
driving the cognitive process in the here-and-now. This is reflected by the fact that the actions performed 
by me and my twin are physically indistinguishable, despite our external differences. 
In the cases we describe, by contrast, the relevant external features are active, playing a crucial role in the 
here-and-now. Because they are coupled with the human organism, they have a direct impact on the 
organism and on its behavior. In these cases, the relevant parts of the world are in the loop, not dangling 
at the other end of a long causal chain. Concentrating on this sort of coupling leads us to an active 
externalism, as opposed to the passive externalism of Putnam and Burge. 
Many have complained that even if Putnam and Burge are right about the externality of content, it is not 
clear that these external aspects play a causal or explanatory role in the generation of action. In 
counterfactual cases where internal structure is held constant but these external features are changed, 
behavior looks just the same; so internal structure seems to be doing the crucial work. We will not 
adjudicate that issue here, but we note that active externalism is not threatened by any such problem. The 
external features in a coupled system play an ineliminable role - if we retain internal structure but change 
the external features, behavior may change completely. The external features here are just as causally 
relevant as typical internal features of the brain.[*] 
*[[Much of the appeal of externalism in the philosophy of mind may stem from the intuitive appeal of active externalism. 
Externalists often make analogies involving external features in coupled systems, and appeal to the arbitrariness of 
boundaries between brain and environment. But these intuitions sit uneasily with the letter of standard externalism. In most 
of the Putnam/Burge cases, the immediate environment is irrelevant; only the historical environment counts. Debate has 
focused on the question of whether mind must be in the head, but a more relevant question in assessing these examples 
might be: is mind in the present?]] 
By embracing an active externalism, we allow a more natural explanation of all sorts of actions. Once 
can explain my choice of words in Scrabble, for example, as the outcome of an extended cognitive 
process involving the rearrangement of tiles on my tray. Of course, one could always try to explain my 
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action in terms of internal processes and a long series of "inputs" and "actions", but this explanation 
would be needless complex. If an isomorphic process were going on in the head, we would feel no urge 
to characterize it in this cumbersome way.[*] In a very real sense, the re-arrangement of tiles on the tray 
is not part of action; it is part of thought. 
*[[Herbert Simon (1981) once suggested that we view internal memory as, in effect, an external resource upon which 
"real" inner processes operate. "Search in memory," he comments, "is not very different from search of the external 
environment." Simon's view at least has the virtue of treating internal and external processing with the parity they deserve, 
but we suspect that on his view the mind will shrink too small for most people's tastes. ]] 
The view we advocate here is reflected by a growing body of research in cognitive science. In areas as 
diverse as the theory of situated cognition (Suchman 1987), studies of real-world-robotics (Beer 1989), 
dynamical approaches to child development (Thelen and Smith 1994), and research on the cognitive 
properties of collectives of agents (Hutchins 1995), cognition is often taken to be continuous with 
processes in the environment.[*] Thus, in seeing cognition as extended one is not merely making a 
terminological decision; it makes a significant difference to the methodology of scientific investigation. 
In effect, explanatory methods that might once have been thought appropriate only for the analysis of 
"inner" processes are now being adapted for the study of the outer, and there is promise that our 
understanding of cognition will become richer for it. 
*[[Philosophicalviews of a similar spirit can be found in Haugeland 1995, McClamrock 1985, Varela et al 1991, and 
Wilson 1994..]] 
Some find this sort of externalism unpalatable. One reason may be that many identify the cognitive with 
the conscious, and it seems far from plausible that consciousness extends outside the head in these cases. 
But not every cognitive process, at least on standard usage, is a conscious process. It is widely accepted 
that all sorts of processes beyond the borders of consciousness play a crucial role in cognitive processing: 
in the retrieval of memories, linguistic processes, and skill acquisition, for example. So the mere fact that 
external processes are external where consciousness is internal is no reason to deny that those processes 
are cognitive. 
More interestingly, one might argue that what keeps real cognition processes in the head is the 
requirement that cognitive processes be portable. Here, we are moved by a vision of what might be 
called the Naked Mind: a package of resources and operations we can always bring to bear on a cognitive 
task, regardless of the local environment. On this view, the trouble with coupled systems is that they are 
too easily decoupled. The true cognitive processes are those that lie at the constant core of the system; 
anything else is an add-on extra. 
There is something to this objection. The brain (or brain and body) comprises a package of basic, 
portable, cognitive resources that is of interest in its own right. These resources may incorporate bodily 
actions into cognitive processes, as when we use our fingers as working memory in a tricky calculation, 
but they will not encompass the more contingent aspects of our external environment, such as a pocket 
calculator. Still, mere contingency of coupling does not rule out cognitive status. In the distant future we 
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may be able to plug various modules into our brain to help us out: a module for extra short-term memory 
when we need it, for example. When a module is plugged in, the processes involving it are just as 
cognitive as if they had been there all along.[*] 
*[[Or consider the following passage from a recent science fiction novel (McHugh 1992, p. 213): "I am taken to the 
system's department where I am attuned to the system. All I do is jack in and then a technician instructs the system to 
attune and it does. I jack out and query the time. 10:52. The information pops up. Always before I could only access 
information when I was jacked in, it gave me a sense that I knew what I thought and what the system told me, but now, 
how do I know what is system and what is Zhang?"]] 
Even if one were to make the portability criterion pivotal, active externalism would not be undermined. 
Counting on our fingers has already been let in the door, for example, and it is easy to push things 
further. Think of the old image of the engineer with a slide rule hanging from his belt wherever he goes. 
What if people always carried a pocket calculator, or had them implanted? The real moral of the 
portability intuition is that for coupled systems to be relevant to the core of cognition, reliable coupling is 
required. It happens that most reliable coupling takes place within the brain, but there can easily be 
reliable coupling with the environment as well. If the resources of my calculator or my Filofax are 
always there when I need them, then they are coupled with me as reliably as we need. In effect, they are 
part of the basic package of cognitive resources that I bring to bear on the everyday world. These systems 
cannot be impugned simply on the basis of the danger of discrete damage, loss, or malfunction, or 
because of any occasional decoupling: the biological brain is in similar danger, and occasionally loses 
capacities temporarily in episodes of sleep, intoxication, and emotion. If the relevant capacities are 
generally there when they are required, this is coupling enough. 
Moreover, it may be that the biological brain has in fact evolved and matured in ways which factor in the 
reliable presence of a manipulable external environment. It certainly seems that evolution has favored on-
board capacities which are especially geared to parasitizing the local environment so as to reduce 
memory load, and even to transform the nature of the computational problems themselves. Our visual 
systems have evolved to rely on their environment in various ways: they exploit contingent facts about 
the structure of natural scenes (e.g. Ullman and Richards 1984), for example, and they take advantage of 
the computational shortcuts afforded by bodily motion and locomotion (e.g. Blake and Yuille, 1992). 
Perhaps there are other cases where evolution has found it advantageous to exploit the possibility of the 
environment being in the cognitive loop. If so, then external coupling is part of the truly basic package of 
cognitive resources that we bring to bear on the world. 
Language may be an example. Language appears to be a central means by which cognitive processes are 
extended into the world. Think of a group of people brainstorming around a table, or a philosopher who 
thinks best by writing, developing her ideas as she goes. It may be that languaged evolved, in part, to 
enable such extensions of our cognitive resources within actively coupled systems. 
Within the lifetime of an organism, too, individual learning may have molded the brain in ways that rely 
on cognitive extensions that surrounded us as we learned. Language is again a central example here, as 
are the various physical and computational artifacts that are routinely used as cognitive extensions by 
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children in schools and by trainees in numerous professions. In such cases the brain develops in a way 
that complements the external structures, and learns to play its role within a unified, densely coupled 
system. Once we recognize that the crucial role of the environment in constraining the evolution and 
development of cognition, we see that extended cognition is a core cognitive process, not an add-on 
extra. 
An analogy may be helpful. The extraordinary efficiency of the fish as a swimming device is partly due, 
it now seems, to an evolved capacity to couple its swimming behaviors to the pools of external kinetic 
energy found as swirls, eddies and vortices in its watery environment (see Triantafyllou and G. 
Triantafyllou 1995). These vortices include both naturally occurring ones (e.g., where water hits a rock) 
and self-induced ones (created by well-timed tail flaps). The fish swims by building these externally 
occurring processes into the very heart of its locomotion routines. The fish and surrounding vortices 
together constit Now consider a reliable feature of the human environment, such as the sea of words. 
This linguistic surround envelopes us from birth. Under such conditions, the plastic human brain will 
surely come to treat such structures as a reliable resource to be factored into the shaping of on-board 
cognitive routines. Where the fish flaps its tail to set up the eddies and vortices it subsequently exploits, 
we intervene in multiple linguistic media, creating local structures and disturbances whose reliable 
presence drives our ongoing internal processes. Words and external symbols are thus paramount among 
the cognitive vortices which help constitute human thought. 
4 From Cognition to Mind
So far we have spoken largely about "cognitive processing", and argued for its extension into the 
environment. Some might think that the conclusion has been bought too cheaply. Perhaps some 
processing takes place in the environment, but what of mind? Everything we have said so far is 
compatiblewith the view that truly mental states - experiences, beliefs, desires, emotions, and so on - are 
all determined by states of the brain. Perhaps what is truly mental is internal, after all? 
We propose to take things a step further. While some mental states, such as experiences, may be 
determined internally, there are other cases in which external factors make a significant contribution. In 
particular, we will argue that beliefs can be constituted partly by features of the environment, when those 
features play the right sort of role in driving cognitive processes. If so, the mind extends into the world. 
First, consider a normal case of belief embedded in memory. Inga hears from a friend that there is an 
exhibition at the Museum of Modern Art, and decides to go see it. She thinks for a moment and recalls 
that the museum is on 53rd Street, so she walks to 53rd Street and goes into the museum. It seems clear 
that Inga believes that the museum is on 53rd Street, and that she believed this even before she consulted 
her memory. It was not previously an occurrent belief, but then neither are most of our beliefs. The belief 
was sitting somewhere in memory, waiting to be accessed. 
Now consider Otto. Otto suffers from Alzheimer's disease, and like many Alzheimer's patients, he relies 
on information in the environment to help structure his life. Otto carries a notebook around with him 
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everywhere he goes. When he learns new information, he writes it down. When he needs some old 
information, he looks it up. For Otto, his notebook plays the role usually played by a biological memory. 
Today, Otto hears about the exhibition at the Museum of Modern Art, and decides to go see it. He 
consults the notebook, which says that the museum is on 53rd Street, so he walks to 53rd Street and goes 
into the museum. 
Clearly, Otto walked to 53rd Street because he wanted to go to the museum and he believed the museum 
was on 53rd Street. And just as Inga had her belief even before she consulted her memory, it seems 
reasonable to say that Otto believed the museum was on 53rd Street even before consulting his notebook. 
For in relevant respects the cases are entirely analogous: the notebook plays for Otto the same role that 
memory plays for Inga. The information in the notebook functions just like the information constituting 
an ordinary non-occurrent belief; it just happens that this information lies beyond the skin. 
The alternative is to say that Otto has no belief about the matter until he consults his notebook; at best, he 
believes that the museum is located at the address in the notebook. But if we follow Otto around for a 
while, we will see how unnatural this way of speaking is. Otto is constantly using his notebook as a 
matter of course. It is central to his actions in all sorts of contexts, in the way that an ordinary memory is 
central in an ordinary life. The same information might come up again and again, perhaps being slightly 
modified on occasion, before retreating into the recesses of his artificial memory. To say that the beliefs 
disappear when the notebook is filed away seems to miss the big picture in just the same way as saying 
that Inga's beliefs disappear as soon as she is longer conscious of them. In both cases the information is 
reliably there when needed, available to consciousness and available to guide action, in just the way that 
we expect a belief to be. 
Certainly, insofar as beliefs and desires are characterized by their explanatory roles, Otto's and Inga's 
cases seem to be on a par: the essential causal dynamics of the two cases mirror each other precisely. We 
are happy to explain Inga's action in terms of her occurrent desire to go to the museum and her standing 
belief that the museum is on 53rd street, and we should be happy to explain Otto's action in the same 
way. The alternative is to explain Otto's action in terms of his occurrent desire to go to the museum, his 
standing belief that the Museum is on the location written in the notebook, and the accessible fact that the 
notebook says the Museum is on 53rd Street; but this complicates the explanation unnecessarily. If we 
must resort to explaining Otto's action this way, then we must also do so for the countless other actions in 
which his notebook is involved; in each of the explanations, there will be an extra term involving the 
notebook. We submit that to explain things this way is to take one step too many. It is pointlessly 
complex, in the same way that it would be pointlessly complex to explain Inga's actions in terms of 
beliefs about her memory. The notebook is a constant for Otto, in the same way that memory is a 
constant for Inga; to point to it in every belief/desire explanation would be redundant. In an explanation, 
simplicity is power. 
If this is right, we can even construct the case of Twin Otto, who is just like Otto except that a while ago 
he mistakenly wrote in his notebook that the Museum of Modern Art was on 51st Street. Today, Twin 
Otto is a physical duplicate of Otto from the skin in, but his notebook differs. Consequently, Twin Otto is 
best characterized as believing that the museum is on 51st Street, where Otto believes it is on 53rd. In 
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these cases, a belief is simply not in the head. 
This mirrors the conclusion of Putnam and Burge, but again there are important differences. In the 
Putnam/Burge cases, the external features constituting differences in belief are distal and historical, so 
that twins in these cases produce physically indistinguishable behavior. In the cases we are describing, 
the relevant external features play an active role in the here-and-now, and have a direct impact on 
behavior. Where Otto walks to 53rd Street, Twin Otto walks to 51st. There is no question of explanatory 
irrelevance for this sort of external belief content; it is introduced precisely because of the central 
explanatory role that it plays. Like the Putnam and Burge cases, these cases involve differences in 
reference and truth-conditions, but they also involve differences in the dynamics of cognition.[*] 
*[[In the terminology of Chalmers' "The Components of Content" (forthcoming): the twins in the Putnam and Burge cases 
differ only in their relational content, but Otto and his twin can be seen to differ in their notional content, which is the sort 
of content that governs cognition. Notional content is generally internal to a cognitive system, but in this case the cognitive 
system is itself effectively extended to include the notebook.]] 
The moral is that when it comes to belief, there is nothing sacred about skull and skin. What makes some 
information count as a belief is the role it plays, and there is no reason why the relevant role can be 
played only from inside the body. 
Some will resist this conclusion. An opponent might put her foot down and insist that as she uses the 
term "belief", or perhaps even according to standard usage, Otto simply does not qualify as believing that 
the museum is on 53rd Street. We do not intend to debate what is standard usage; our broader point is 
that the notion of belief ought to be used so that Otto qualifies as having the belief in question. In all 
important respects, Otto's case is similar to a standard case of (non-occurrent) belief. The differences 
between Otto's case and Inga's are striking, but they are superficial. By using the "belief" notion in a 
wider way, it picks out something more akin to a natural kind. The notion becomes deeper and more 
unified, and is more useful in explanation. 
To provide substantial resistance, an opponent has to show that Otto's and Inga's cases differ in some 
importantand relevant respect. But in what deep respect are the cases different? To make the case solely 
on the grounds that information is in the head in one case but not in the other would be to beg the 
question. If this difference is relevant to a difference in belief, it is surely not primitively relevant. To 
justify the different treatment, we must find some more basic underlying difference between the two. 
It might be suggested that the cases are relevantly different in that Inga has more reliable access to the 
information. After all, someone might take away Otto's notebook at any time, but Inga's memory is safer. 
It is not implausible that constancy is relevant: indeed, the fact that Otto always uses his notebook played 
some role in our justifying its cognitive status. If Otto were consulting a guidebook as a one-off, we 
would be much less likely to ascribe him a standing belief. But in the original case, Otto's access to the 
notebook is very reliable - not perfectly reliable, to be sure, but then neither is Inga's access to her 
memory. A surgeon might tamper with her brain, or more mundanely, she might have too much to drink. 
The mere possibility of such tampering is not enough to deny her the belief. 
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Perhaps the intuition that Otto's is not a true belief comes from a residual feeling that the only true beliefs 
are occurrent beliefs. If we take this feeling seriously, Inga's belief will be ruled out too, as will many 
beliefs that we attribute in everyday life. This would be an extreme view, but it may be the most 
consistent way to deny Otto's belief. Upon even a slightly less extreme view - the view that a belief must 
be available for consciousness, for example - Otto's notebook entry seems to qualify just as well as Inga's 
memory. Once dispositional beliefs are let in the door, it is difficult to resist the conclusion that Otto's 
notebook has all the relevant dispositions. 
5 Beyond the Outer Limits
If the thesis is accepted, how far should we go? All sorts of puzzle cases spring to mind. What of the 
amnesic villagers in 100 Years of Solitude, who forget the names for everything and so hang labels 
everywhere? Does the information in my Filofax count as part of my memory? If Otto's notebook has 
been tampered with, does he believe the newly-installed information? Do I believe the contents of the 
page in front of me before I read it? Is my cognitive state somehow spread across the Internet? 
We do not think that there are categorical answers to all of these questions, and we will not give them. 
But to help understand what is involved in ascriptions of extended belief, we can at least examine the 
features of our central case that make the notion so clearly applicable there. First, the notebook is a 
constant in Otto's life - in cases where the information in the notebook would be relevant, he will rarely 
take action without consulting it. Second, the information in the notebook is directly available without 
difficulty. Third, upon retrieving information from the notebook he automatically endorses it. Fourth, the 
information in the notebook has been consciously endorsed at some point in the past, and indeed is there 
as a consequence of this endorsement.[*] The status of the fourth feature as a criterion for belief is 
arguable (perhaps one can acquire beliefs through subliminal perception, or through memory 
tampering?), but the first three features certainly play a crucial role. 
*[[The constancy and past-endorsement criteria may suggest that history is partly constitutive of belief. One might react to 
this by removing any historical component (giving a purely dispositional reading of the constancy criterion and eliminating 
the past-endorsement criterion, for example), or one might allow such a component as long as the main burden is carried 
by features of the present.]] 
Insofar as increasingly exotic puzzle cases lack these features, the applicability of the notion of "belief" 
gradually falls of. If I rarely take relevant action without consulting my Filofax, for example, its status 
within my cognitive system will resemble that of the notebook in Otto's. But if I often act without 
consultation - for example, if I sometimes answer relevant questions with "I don't know" - then 
information in it counts less clearly as part of my belief system. The Internet is likely to fail on multiple 
counts, unless I am unusually computer-reliant, facile with the technology, and trusting, but information 
in certain files on my computer may qualify. In intermediate cases, the question of whether a belief is 
present may be indeterminate, or the answer may depend on the varying standards that are at play in 
various contexts in which the question might be asked. But any indeterminacy here does not mean that in 
the central cases, the answer is not clear. 
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One might worry that Otto's access to his notebook in fact comes and goes. He showers without the 
notebook, for example, and he cannot read it when it is dark. Surely his belief cannot come and go so 
easily? We could get around this problem by redescribing the situation, but in any case an occasional 
temporary disconnection does not threaten our claim. After all, when Inga is asleep, or when she is 
intoxicated, we do not say that her belief disappears. What really counts is that the information is easily 
available when the subject needs it, and this constraint is satisfied equally in the two cases. If Otto's 
notebook were often unavailable to him at times when the information in it would be useful, there might 
be a problem, as the information would not be able to play the action-guiding role that is central to belief; 
but if it is easily available in most relevant situations, the belief is not endangered. 
Perhaps a difference is that Inga has better access to the information than Otto does? Inga's "central" 
processes and her memory probably have a relatively high-bandwidth link between them, compared to 
the low-grade connection between Otto and his notebook. But this alone does not make a difference 
between believing and not believing. Consider Inga's museum-going friend Lucy, whose biological 
memory has only a low-grade link to her central systems, due to nonstandard biology or past 
misadventures. Processing in Lucy's case might be less efficient, but as long as the relevant information 
is accessible, Lucy clearly believes that the museum is on 53rd Street. If the connection was too indirect - 
if Lucy had to struggle hard to retrieve the information with mixed results, or a psychotherapist's aid 
were needed - we might become more reluctant to ascribe the belief, but such cases are well beyond 
Otto's situation, in which the information is easily accessible. 
Another suggestion could be that Otto has access to the relevant information only by perception, whereas 
Inga has more direct access -- by introspection, perhaps. In some ways, however, to put things this way is 
to beg the question. After all, we are in effect advocating a point of view on which Otto's internal 
processes and his notebook constitute a single cognitive system. From the standpoint of this system, the 
flow of information between notebook and brain is not perceptual at all; it does not involve the impact of 
something outside the system. It is more akin to information flow within the brain. The only deep way in 
which the access is perceptual is that in Otto's case, there is a distinctly perceptual phenomenology 
associated with the retrieval of the information, whereas in Inga's case there is not. But why should the 
nature of an associated phenomenology make a difference to the status of a belief? Inga's memory mayhave some associated phenomenology, but it is still a belief. The phenomenology is not visual, to be sure. 
But for visual phenomenology consider the Terminator, from the Arnold Schwarzenegger movie of the 
same name. When he recalls some information from memory, it is "displayed" before him in his visual 
field (presumably he is conscious of it, as there are frequent shots depicting his point of view). The fact 
that standing memories are recalled in this unusual way surely makes little difference to their status as 
standing beliefs. 
These various small differences between Otto's and Inga's cases are all shallow differences. To focus on 
them would be to miss the way in which for Otto, notebook entries play just the sort of role that beliefs 
play in guiding most people's lives. 
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What about socially extended cognition? Could my mental states be partly constituted by the states of 
other thinkers? We see no reason why not, in principle. In an unusually interdependent couple, it is 
entirely possible that one partner's beliefs will play the same sort of role for the other as the notebook 
plays for Otto.[*] What is central is a high degree of trust, reliance, and accessibility. In other social 
relationships these criteria may not be so clearly fulfilled, but they might nevertheless be fulfilled in 
specific domains. For example, the waiter at my favorite restaurant might act as a repository of my 
beliefs about my favorite meals (this might even be construed as a case of extended desire). In other 
cases, one's beliefs might be embodied in one's secretary, one's accountant, or one's collaborator.[*] 
*[[From the New York Times, March 30, 1995, p.B7, in an article on former UCLA basketball coach John Wooden: 
"Wooden and his wife attended 36 straight Final Fours, and she invariably served as his memory bank. Nell Wooden rarely 
forgot a name - her husband rarely remembered one - and in the standing-room-only Final Four lobbies, she would 
recognize people for him."]] 
*[[Might this sort of reasoning also allow something like Burge's extended "arthritis" beliefs? After all, I might always 
defer to my doctor in taking relevant actions concerning my disease. Perhaps so, but there are some clear differences. For 
example, any extended beliefs would be grounded in an existing active relationship with the doctor, rather than in a 
historical relationship to a language community. And on the current analysis, my deference to the doctor would tend to 
yield something like a true belief that I have some other disease in my thigh, rather than the false belief that I have arthritis 
there. On the other hand, if I used medical experts solely as terminological consultants, the results of Burge's analysis 
might be mirrored.]] 
In each of these cases, the major burden of the coupling between agents is carried by language. Without 
language, we might be much more akin to discrete Cartesian "inner" minds, in which high-level 
cognition relies largely on internal resources. But the advent of language has allowed us to spread this 
burden into the world. Language, thus construed, is not a mirror of our inner states but a complement to 
them. It serves as a tool whose role is to extend cognition in ways that on-board devices cannot. Indeed, 
it may be that the intellectual explosion in recent evolutionary time is due as much to this linguistically-
enabled extension of cognition as to any independent development in our inner cognitive resources. 
What, finally, of the self? Does the extended mind imply an extended self? It seems so. Most of us 
already accept that the self outstrips the boundaries of consciousness; my dispositional beliefs, for 
example, constitute in some deep sense part of who I am. If so, then these boundaries may also fall 
beyond the skin. The information in Otto's notebook, for example, is a central part of his identity as a 
cognitive agent. What this comes to is that Otto himself is best regarded as an extended system, a 
coupling of biological organism and external resources. To consistently resist this conclusion, we would 
have to shrink the self into a mere bundle of occurrent states, severely threatening its deep psychological 
continuity. Far better to take the broader view, and see agents themselves as spread into the world. 
As with any reconception of ourselves, this view will have significant consequences. There are obvious 
consequences for philosophical views of the mind and for the methodology of research in cognitive 
science, but there will also be effects in the moral and social domains. It may be, for example, that in 
some cases interfering with someone's environment will have the same moral significance as interfering 
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with their person. And if the view is taken seriously, certain forms of social activity might be 
reconceived as less akin to communication and action, and as more akin to thought. In any case, once the 
hegemony of skin and skull is usurped, we may be able to see ourselves more truly as creatures of the 
world. 
REFERENCES 
Beer, R. 1989. Intelligence as Adaptive Behavior. New York: Academic Press. 
Blake, A. & Yuille, A. (eds) 1992. Active Vision. Cambridge, MA: MIT Press. 
Burge, T. 1979. Individualism and the mental. Midwest Studies in Philosophy 4:73-122. 
Clark, A. 1989. Microcognition. MIT Press. 
Haugeland, J. 1995. Mind embodied and embedded. In (Y. Houng and J. Ho, eds.), Mind and Cognition. 
Taipei: Academia Sinica. 
Hutchins, E. 1995. Cognition in the Wild. Cambridge, MA: MIT Press, 
Kirsh, D. 1995. The intelligent use of space. Artificial Intelligence 73:31-68. 
Kirsh, D. & Maglio, P. 1994. On distinguishing epistemic from pragmatic action. Cognitive Science 
18:513-49. 
McClamrock, R. 1995. Existential Cognition. Chicago: University of Chicago Press. 
McClelland, J.L, D.E. Rumelhart, & G.E. Hinton 1986. The appeal of parallel distributed processing". In 
(McClelland & Rumelhart, eds) Parallel Distributed Processing, Volume 2. Cambridge, MA: MIT Press. 
McHugh, M. 1992. China Mountain Zhang. New York: Tom Doherty Associates. 
Putnam, H. 1975. The meaning of `meaning'. In (K. Gunderson, ed) Language, Mind, and Knowledge. 
Minneapolis: University of Minnesota Press. 
Simon, H. 1981. The Sciences of the Artificial. MIT Press. 
Suchman, L. 1987. Plans and Situated Actions. Cambridge, UK: Cambridge University Press. 
Thelen, E. & Smith, L. 1994. A Dynamic Systems Approach to the Development of Cognition and Action. 
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On Sense and Intension
On Sense and Intension
David J. Chalmers 
Department of Philosophy
University of Arizona
Tucson, AZ 85721.
chalmers@arizona.edu
What is involved in the meaning of our expressions? Frege suggested that there is an aspect of an 
expression's meaning - the expression's sense - that is constitutively tied to the expression's role in reason 
and cognition. Many contemporary philosophers have argued that there is no such aspect of meaning. I 
think that Frege was closer to the truth: one can make good sense of an aspect of meaning with many, 
although not all, of the properties that Frege attributed to sense. One can naturally associate an expression 
with an epistemic intension - a function from epistemic possibilities to extensions - such that an 
expression's epistemic intension is deeply tied to its role in reason and cognition, and such that it has 
many of the properties attributed to Fregean sense. I will argue that the claim that expressions have 
associated intensions of this sort is undefeated by the major contemporary arguments against Fregeansense. 
1 Introduction
The simplest aspect of an expression's meaning is its extension. We can stipulate that the extension of a 
sentence is its truth-value, and that the extension of a singular term is its referent. The extension of other 
expressions can be seen as associated entities that contributes to the truth-value of a sentence in a manner 
broadly analogous to the way in which the referent of a singular term contributes to the truth-value of a 
sentence. In many cases, the extension of an expression will be what we intuitively think of as its referent, 
although this need not hold in all cases, as the case of sentences illustrates. While Frege himself is often 
interpreted as holding that a sentence's truth-value is its referent, this claim is counterintuitive and widely 
disputed. We can avoid that issue in the present framework by using the technical term 'extension'; in this 
context, the claim that the extension of a sentence is its truth-value is a stipulation. 
Different sorts of expressions have different sorts of extensions. By the stipulation above, the extension of 
a singular term is an individual: the extension of 'France' is a particular country (France), and the 
extension of 'Bill Clinton' is a particular person (Clinton). Analogously, the extension of a general term is 
plausibly seen as a class: the extension of 'cat' is a particular class of animals (the class of cats). The 
extension of a kind term can be seen as a kind: the extension of 'water' is a particular substance (water). 
The extension of a predicate can be seen as a property or perhaps as a class: the extension of 'hot' is a 
particular property (hotness) or a particular class (the class of hot things). 
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The extensions of expressions can at least often be used to determine the extensions of complex 
expressions of which they are parts. This applies most obviously to the truth-values of sentences. For 
example, 'Sydney is in Australia' is true, and it is true because the extension of 'Sydney' (a particular city) 
is located in the extension of 'Australia' (a particular country). 'Michael Jordan is short' is false, and it is 
false because the individual who is the extension of 'Michael Jordan' does not have the property that is the 
extension of 'short'. This also applies to complex expressions shorter than sentences: for example, it is not 
implausible that the complex singular term 'the greatest cricket player' has an extension (Don Bradman), 
and that this extension is determined by the extensions of its parts. 
There are various complexities here, and there are corresponding choices to be made. For example, some 
terms (e.g. 'Santa Claus') appear to have no referent: in such a case, one might say that they lack 
extension, or one might say that they have a null extension. In some cases (e.g. 'greatest' above), it 
appears that the extension of an expression can depend on context: for this reason, we may wish to assign 
extensions to expression tokens, or to expression types in contexts, rather than to expression types alone. 
In general, the truth-value of a sentence will be determined by the extensions of its parts within a 
regimented logical form, along with corresponding principles for determining truth-value of a regimented 
sentence from its logical form and the extensions of its parts; and the regimented sentence may look quite 
different from the original sentence, with different basic constituents and a more complex structure. 
Different semantic theories may assign extensions to expressions and logical forms to sentences in 
different ways. 
Many of these complexities will not concern us here. The discussion that follows should be general over 
many specific proposals concerning logical form, extensions of simple terms, and compositional 
determination. I will simply take it for granted that sentences have a logical form and contain simple 
terms that have an extension; that these simple terms compose complex terms, which compose the 
sentence; and that the extension of a complex expression (including a sentence) is at least in many cases 
determined by its logical form and the extensions of its parts. 
To clarify terminology: On my usage, an 'expression' is any entity that has an extension (or which is a 
candidate for extension). For ease of discussion, I will say that when an expression is of the sort that is a 
candidate for an extension, but appears to lack extension, it has a null extension. A 'term' is any 
expression other than a sentence. Complex expressions are expressions (including sentences) that are 
composed of other expressions. Complex terms are terms that are composed of other terms. Simple terms 
are terms that are not composed of other terms. 
2 Sense and extension
A simple and attractive view of meaning ties the meaning of an expression to its extension. On such a 
view, the meaning of a simple term is its extension, and the meaning of a complex expression is 
determined by the extensions of its parts. On the strongest version of this view, the meaning of a complex 
expression is its extension. On a slightly weaker version, the meaning of a complex expression is a 
complex structure involving the extensions of the simple terms that are parts of the expression. Either 
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way, all meaning is grounded in extension. 
There are three traditional reasons for doubting this simple view of meaning. First: some simple terms 
(such as 'Santa Claus' and 'phlogiston') appear to lack extension. On the view above, these terms will lack 
meaning, or they will all have the same trivial meaning, corresponding to the null extension. But 
intuitively it seems clear that these terms have some meaning, and that their meanings differ from each 
others'. If so, then meaning is more than extension. 
Second: in some sentences, the role of a word in determining the sentence's truth-value appears to go 
beyond its extension. This applies especially to sentences about beliefs and related matters. For example, 
it is plausible that `John believes that Cary Grant is an actor' could be true, while `John believes that 
Archie Leach is an actor' is false, even though `Cary Grant' and `Archie Leach' have the same extension. 
If so, then either the truth-value of the sentence is not determined by the meanings of the terms, or there is 
more to meaning than reference. 
Third: there is often more than one term referring to the same thing. In such cases, the terms often seem 
intuitively to have different meanings. Witness `Hesperus', the ancients' name for the evening star, and 
`Phosphorus', their name for the morning star. Or take `water' and `H2O', both of which refer to the same 
substance. If `water' and `H2O' refer to the same thing, and if reference is all there is to meaning, then 
`water' and `H2O' refer to the same thing. But intuitively, `water' and `H2O' have different meanings. If 
that is so, then reference cannot be all there is to meaning. 
In "Über Sinn und Bedeutung" (1891), Frege lays out the central issue roughly as follows. The sentence 
`Hesperus is Hesperus' is trivial. It can be known a priori, or without any appeal to experience. The 
knowledge that Hesperus is Hesperus requires almost no cognitive work at all, and gives us no significant 
information about the world. But the sentence `Hesperus is Phosphorus' is nontrivial. It can only be 
known a posteriori, by appeal to much empirical experience. The knowledge that Hesperus is Phosphorus 
requires much cognitive work, and gives us significant information about the world. 
As Frege put it, `Hesperus is Phosphorus' is cognitively significant whereas `Hesperus is Hesperus' is not. 
And intuitively,this difference in cognitive significance reflects a difference in the meanings of 
`Hesperus' and `Phosphorus'. When a subject comes to know that `Hesperus is Phosphorus', what she 
learns depends on what she means by `Hesperus' and by `Phosphorus'. And intuitively, the subject learns 
something different when she learns that Hesperus is Phosphorus than when she learns that Hesperus is 
Hesperus. If these two claims are correct, then `Hesperus' and `Phosphorus' have different meanings, and 
then meaning involves more than extension. 
If meaning involves more than extension, then what is the further element? Frege held that in addition to 
extension (or reference), an expression also has a sense. `Hesperus' and `Phosphorus' have the same 
referent, but different senses. `Water' and `H2O' have the same referent, but different senses. `Cary Grant' 
and `Archie Leach' have the same referent, but different senses. For all such cases, the intuitive difference 
in cognitive significance among pairs of terms such as these is reflected in a difference in the terms' 
senses. 
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On Sense and Intension
The notion of sense has a number of important features, which I discuss in what follows. The discussion 
is intended as a broad and informal outline of a Fregean view, rather than as a faithful and representation 
of every feature of Frege's own view. Later, I will give more precise versions of some of these claims. 
(1) Every expression that has an extension has a sense. 
In "Über Sinn und Bedutung", Frege concentrated mostly on the senses of names, holding that all names 
have a sense. But the same considerations apply to any expression that has an extension. Two general 
terms can have the same extension and different cognitive significance; two predicates can have the same 
extension and different cognitive significance; two sentences can have the same extension and different 
cognitive significance. So general terms, predicates, and sentences all have senses as well as extensions. 
The same goes for any expression that has an extension, or is a candidate for extension. 
(2) Sense reflects cognitive significance. 
The central feature of sense is that it is tied constitutively to cognitive significance. In the case of singular 
terms, Frege set out this connection as follows: two referring expressions `a' and `b' have different senses 
if and only if an identity statement `a=b' is cognitively significant. So `Hesperus' and `Phosphorus' have 
different senses, since `Hesperus is Phosphorus' is cognitively significant. `Hesperus is Hesperus', by 
contrast, is cognitively insignificant, and two sides of the identity correspondingly have the same sense. 
One can naturally generalize this test to other expressions: a pair of expressions of the same type have 
different senses when a statement of their coextensiveness is cognitively significant. In the case of kind 
terms, one can apply the same test as before: 'a' and 'b' have different senses if and only if an identity 
statement 'a=b' is cognitively significant. So 'water' and 'H2O' have different senses, since 'water is H2O' 
is cognitively significant. In other cases, the test wil be slightly different. For general terms, one can say 
that 'a' and 'b' have different senses when 'All a's are b's and all b's are a's' is cognitively significant: so 
'renate' and 'cordate' have different senses. For predicates, one can say that 'A' and 'B' have different 
senses when 'For all x, x is A iff x is B' is cognitively significant: so 'has a heart' and 'has a kidney' have 
different senses. For sentences, one can say that S and T have different senses when 'S iff T' is cognitively 
significant: so 'Hesperus is a planet' and 'Phosphorus is a planet' have different senses. 
It is possible for two different expressions to have the same sense. When two words are intuitively 
synonymous - `lawyer' and `attorney'. perhaps - an identity between them is cognitively insignificant. The 
truth of `lawyers are attorneys' is arguably trivial: it is knowable a priori, requires no cognitive work, and 
gives no significant information about the world. If so, then `lawyer' and `attorney' have the same sense. 
In a similar way, it is plausible that the sentences 'Vixens are rare' and 'Female foxes are rare' are trivially 
equivalent. If so, the two sentences have the same sense. 
We can think of the sense of an expression as mirroring the expression's role in reason and cognition. 
When two expressions are trivially equivalent, they will play almost the same role in reason and 
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On Sense and Intension
cognition, and will have the same sense. When two expressions are not trivially equivalent, they will play 
different roles in reason and cognition, and will have different senses. In this way, we can think of an 
expression's sense as capturing its cognitive significance, and as representing the "cognitive value" or 
"cognitive content" if the expression. 
*[[Here and throughout the paper, I follow the convention of using sentence symbols such as S, which usually refer to a 
sentence, to substitute for the sentence in quotational contexts, indirect contexts, and other contexts in which it is clear that 
S is being used, not mentioned.]] 
(3) The sense of a complex expression depends on the senses of its parts. 
We saw before that the extension of a sentence (such as `John is hot and Mary is cold') at least typically 
depends on the extension of the expressions it contains and on its logical form. In a similar way, the sense 
of a sentence at least typically depends on the senses of the expressions it contains and its logical form. 
The same goes for complex terms, such as 'the greatest cricket player': insofar as its extension depends on 
the extensions of its parts, its sense depends on the sense of its parts. 
This dependence of sense on sense may proceed in much the same way as the dependence of extension on 
extension. We first determine the logical form of a complex expresion, then determine the senses of the 
basic terms involved, and then compose these senses in a way that depends on the logical form, to 
determine the sense of the complex expression. Just how this composition works is not quite clear, but I 
will say more about it in what follows. 
(4) Sense determines extension. 
Frege held that the extension of a word, a complex expression, or a sentence is determined in some way 
by its sense. He was not entirely clear about just what sort of determination is involved here. One way of 
understanding the idea is the following: if two expressions have the same sense, then they have the same 
extension. The reverse need not be true: we have seen that it is possible two terms to have the same 
extension, but different sense. So there is no path from extension to sense, in general. But if this claim is 
right, then there is a path from sense to extension. 
One question is whether sense determines extension on its own, or whether something else contributes to 
determining the extension. If the former, then it seems that the extension must somehow be present at 
least implicitly within the sense. But it is not easy to see how this could work, at least if sense is taken to 
reflect cognitive significance. The two terms `the morning star' and `the evening star' have the same 
extension, for example, but it is not clear how this sameness of extension is present within the term's 
senses. Similarly, a statement such as `There are 90 chemical elements that occur in nature' may be true, 
but it is not clear how the truth of the sentence is determined by its sense alone. So it is natural to think 
that something else must contribute: namely, the world. Intuitively, the sentence above is