This article originally appeared on NYU’s website.
Where does the mind stop and the rest of the world begin? The question invites two standard replies. Some accept the boundaries 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.
Consider three cases of human problem-solving:
- 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.
- 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.
- 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 par with case (1). And case (2) with the rotation button displays the same sort of computational structure as case (3), 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 case just 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.
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, the use of physical re-arrangements of letter tiles to prompt word recall in Scrabble, the use of instruments such as the nautical slide rule, 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!
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 from the 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.
By embracing an active externalism, we allow a more natural explanation of all sorts of actions. One can explain my choice of words in Scrabble, for example, as an outcome of an extended cognitive process involving the rearrangement of tiles on my tray. Of course, one could always try to explain my action in terms of internal processes and a long series of ‘inputs’ and ‘actions,’ but this explanation would be needlessly 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.
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 though 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.
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 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.
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 of 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 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 short cuts 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.
Another example may be language, which 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 language 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 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 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.
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 brought too cheaply. Perhaps some processing takes place in the environment, but what of mind? Everything we have said so far is compatible with 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 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 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 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 the 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 no 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 at 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 in 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 a 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 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.
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 important and relevant respect. But in what deep respect are these 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 rain, or more mundanely, she might have too much to drink. The mere possibility of such tampering is not enough to deny her the belief.
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 disappear. 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 may have 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.
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.
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 One Hundred Years of Solitude, who forget the names of 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.
Insofar as increasingly exotic puzzle cases lack these features, the applicability of the notion of ‘belief’ gradually falls off. 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.
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.
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 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.
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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? ↩
Philosophical views of a similar spirit can be found in Haugeland 1995, McClamrock 1995, Varela et al. 1991, and Wilson 1994. ↩
In the terminology of Chalmers (forthcoming): the twins in the Putnam and Burge cases differ only in their relational content (secondary intension), but Otto and his twin can be seen to differ in their notional content (primary intension), 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 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. ↩