A Problem In Hume


A Problem in Hume




Early in the TreatiseHume sets out to establish what he calls a “general proposition”, namely: “That all our simple ideas in their first appearance are deriv’d from simple impressions, which are correspondent to them, and which they exactly represent” (Book I, Section I, p.52).[1]What kind of proposition is this? It is evidently a causal proposition, to the effect that ideas are caused by impressions, and not vice versa: the word “deriv’d” indicates causality. So Hume’s general proposition concerns a type of mental causation linking impressions and ideas; accordingly, it states a psychological causal law. It is not like a mathematical generalization that expresses mere “relations of ideas”, so it is not known a priori. As if to confirm this interpretation of his meaning, Hume goes on to say:  “The constant conjunction of our resembling perceptions [impressions and ideas], is a convincing proof, that the one are the causes of the other; and this priority of the impressions is an equal proof, that our impressions are the causes of our ideas, not our ideas of our impressions” (p. 53). Thus we observe the constant conjunction of impressions and ideas, as well as the temporal priority of impressions over ideas, and we infer that the two are causally connected, with impressions doing the causing. In Hume’s terminology, we believe his general proposition on the basis of “experience”—our experience of constant conjunction.

But this means that Hume’s own critique of causal belief applies to his guiding principle. In brief: our causal beliefs are not based on insight into the real powers of cause and effect but on mere constant conjunctions that could easily have been otherwise, and which interact with our instincts to produce non-rational beliefs of an inductive nature. It is like our knowledge of the actions of colliding billiard balls: the real powers are hidden and our experience of objects is consistent with anything following anything; we are merely brought by custom and instinct to expect a particular type of effect when we experience a constant conjunction (and not otherwise). Thus induction is not an affair of reason but of our animal nature (animals too form expectations based on nothing more than constant conjunction). Skepticism regarding our inductive inferences is therefore indicated: induction has no rational foundation. For example, prior to our experience of constant conjunction ideas might be the cause of impressions, or ideas might have no cause, or the impression of red might cause the idea of blue, or impressions might cause heart palpitations. We observe no “necessary connexion” between cause and effect and associate the two only by experience of regularity—which might break down at any moment. Impressions have caused ideas so far but we have no reason to suppose that they will continue to do so—any more than we have reason to expect billiard balls to impart motion as they have hitherto. Hume’s general proposition is an inductive generalization and hence falls under his strictures regarding our causal knowledge (so called); in particular, it is believed on instinct not reason.

Why is this a problem for Hume? Because his own philosophy is based on a principle that he himself is committed to regarding as irrational—mere custom, animal instinct, blind acceptance. He accepts a principle—a crucial principle–that he has no reasonto accept. It might be that the idea of necessary connexion, say, is an exception to the generalization Hume has arrived at on the basis of his experience of constant conjunction between impressions and ideas—the equivalent of a black swan. Nothing in our experience can logically rule out such an exception, so we cannot exclude the idea based on anything we have observed. The missing shade of blue might also simply be an instance in which the generalization breaks down. There is no necessityin the general proposition Hume seeks to establish, by his own lights–at any rate, no necessity we can know about. Hume’s philosophy is therefore self-refuting. His fundamental empiricist principle—all ideas are derived from impressions—is unjustifiable given his skepticism about induction. Maybe we can’t helpaccepting his principle, but that is just a matter of our animal tendencies not a reflection of any foundation in reason. It is just that when we encounter an idea our mind suggests the existence of a corresponding impression because that is what we have experienced so far—we expectto find an impression. But that is not a rational expectation, merely the operation of brute instinct. Hume’s entire philosophy thus rests on a principle that he himself regards as embodying an invalid inference.

It is remarkable that Hume uses the word “proof” as he does in the passage quoted above: he says there that the constant conjunction of impressions and ideas gives us “convincing proof” that there is a causal relation that can be relied on in new cases. Where else would Hume say that constant conjunction gives us “convincing proof” of a causal generalization? His entire position is that constant conjunction gives us no such “proof” but only inclines us by instinct to have certain psychological expectations. And it is noteworthy that in the Enquiry, the more mature work, he drops all such talk of constant conjunction, causality, and proof in relation to his basic empiricist principle, speaking merely of ideas as “derived” from impressions. But we are still entitled to ask what manner of relation this derivation is, and it is hard to see how it could be anything but causality given Hume’s general outlook. Did he come to see the basic incoherence of his philosophy and seek to paper over the problem? He certainly never directly confronts the question of whether his principle is an inductive causal generalization, and hence is subject to Humean scruples about such generalizations.

It is clear from the way he writes that Hume does not regard his principle as a fallible inference from constant conjunctions with no force beyond what experience has so far provided. He seems to suppose that it is something like a conceptual or necessary truth: there couldnot be a simple idea that arose spontaneously without the help of an antecedent sensory impression—as (to use his own example) a blind man necessarily cannot have ideas of color. The trouble is that nothing in his official philosophy allows him to assert such a thing: there are only “relations of ideas” and “matters of fact”, with causal knowledge based on nothing but “experience”. His principle has to be a causal generalization, according to his own standards, and yet to admit that is to undermine its power to do the work Hume requires of it. Why shouldn’t the ideas of space, time, number, body, self, and necessity all be exceptions to a generalization based on a past constant conjunction of impressions and ideas? Sometimes ideas are copies of impressions but sometimes they may not be—there is no a priori necessity about the link. That is precisely what a rationalist like Descartes or Leibniz will insist: there are many simple ideas that don’t stem from impressions; it is simply a bad induction to suppose otherwise.

According to Hume’s general theory of causation, we import the idea of necessary connexion from somewhere “extraneous and foreign”[2]to the causal relation itself, i.e. from the mind’s instinctual tendency to project constant conjunctions. This point should apply as much to his general proposition about ideas and impressions as to any other causal statement: but then his philosophy rests upon the same fallacy–he has attributed to his principle a necessity that arises from within his own mind. He should regard the principle as recording nothing more than a constant conjunction that he has so far observed, so that his philosophy might collapse at any time. Maybe tomorrow ideas will notbe caused by impressions but arise in the mind ab initio. Nowhere does Hume ever confront such a possibility, but it is what his general position commits him to.



[1]David Hume, A Treatise of Human Nature(Penguin Books, 1969; originally published 1739).

[2]The phrase is from Section VII, [26], p. 56 of An Enquiry Concerning Human Understanding(Oxford University Press, 2007).


Is Solipsism Logically Possible?



Is Solipsism Logically Possible?



It has been commonly assumed that solipsism is logically or metaphysically possible. I could exist without anything else existing. There are possible worlds in which I exist and nothing else does. I can imagine myself completely alone. Seductive as such thoughts may appear, I think they are mistaken; they arise from a confusion of metaphysical and epistemic possibility.

Suppose someone claims that this table in front of me could exist in splendid isolation, the sole occupant of an ontologically impoverished world—no chairs, planets, people, birds, etc. Well, thatseems true—those absences are logically possible. But what about the piece of wood the table is made of? This table is made of that piece of wood in every possible world in which it exists, so the table cannot exist without the piece of wood. But that piece of wood came from a particular tree—it could not have come from any other tree. So this table can only exist in a world that alsocontains the tree in question, since it was a part of that tree. The table and the tree are distinct existences, so the table cannot exist without something elseexisting—the tree that donated the part that composes it. The table is necessarily composed of that piece of wood and that piece of wood necessarily derives from a particular tree: there are necessities linking the table with another object, viz. the tree. Thus “solipsism” with respect to this table is not logically possible.

Now consider a person, say me. I could not exist without my parents existing, since no person could be thisindividual and not be born to my parents. This is the necessity of origin as applied to persons. In any world in which I exist my parents exist; more precisely, in any world in which I exist a particular sperm and egg exist (and they can exist only because of the human organisms that produced them). So my existence implies the existence of my parents. Therefore solipsism is not logically possible. But the existential ramifications go further: my parents cannot exist in a world in which theirparents don’t exist. And so on back down the ancestral line, till we get to the origin of life: no later organism can exist without the procreative organisms in its ancestral line. Every organism has an origin, and that origin is essential to its identity. But it goes even further, because the very first organism must have had its own inorganic origin, presumably in a clump of molecules, and that origin is essential to it—itcould not exist without thatclump existing. And that clump of molecules also had an origin, possibly in element-forming stars; so it couldn’t exist without the physical entities that gave rise to it. And those physical entities go back to the big bang, originating in some sort of super-hot plasma. So I (thisperson) could not exist unless the whole chain existed, up to and including certain components of the big bang. Colin McGinn could not exist without millions and millions of other things existing, granted the necessity of origin. I am linked by hard necessity to an enormous sequence of distinct particulars. I couldn’t be mewithout them.

Of course, there could be someone just likeme that exists in the absence of my specific generative sequence—though he too will necessarily carry his own generative sequence. Perhaps in some remote possible world this counterpart of mine arises not by procreation but by instantaneous generation—say, by lightning rearranging the molecules in a swamp. But even then that individual would not be able to exist without hisparticular origins—his collection of swampy molecules and that magical bolt of lightning. Solipsism will not be logically possible even for him. In any case, the question is irrelevant to whether Icould exist without my generative sequence: my counterparts are not identical to me. All we are claiming is that solipsism is logically impossible so far as Iam concerned—this specific human being. It is myexistence that logically (metaphysically) requires the existence of other things—lots of other things. I (Colin McGinn) could never exist in another possible world and peer out over it to find nothing but myself (at least throughout history–I might exist without any other organism existing at the same time as me, my parents both being dead). The same applies to any person with the kind of origin I have, i.e. all human beings.

Why do we feel resistance to these crushingly banal points? I think it is in part because we confuse a metaphysical question with an epistemological question; and we cannot answer the epistemological question by appealing to our answer to the metaphysical question. The epistemological question is whether I can now provethat solipsism is false: can I establish that I am not alone in the universe? In particular, can I establish that my parents really exist (or existed)? Maybe they are just figments of my imagination; maybe I was conceived by lightning and swamp. I cannot be certainthat I was not. I cannot even be certain that I have a body. I can establish that I think and exist, but I cannot get beyond that in the quest for certainty. So the existence of my parents is not an epistemicnecessity. If I could prove that I am a member of a particular biological species, then maybe I could prove that I must have arisen by sexual reproduction from other members of that species: but the skeptic is not going to let that by–she will demand that I demonstrate that I ama particular kind of organism arising by sexual reproduction. And I will not be able to meet that challenge, since there are conceivable alternatives to it (the hand of God, swamp and lightning, the dream hypothesis). Maybe I just imaginethat I am a biological entity with parents and an evolutionary history. So we cannot disprove solipsism in the epistemological sense: for all I know, there is nothing in the universe apart from me.

But this is perfectly compatible with the thesis that it is not in factlogically possible for me to exist without other entities existing along with me: for if I ama biological entity born by procreation, then my existence logically implies the existence of many other things. It is just that I cannot prove to the skeptic’s satisfaction (or my own) that that is what I am. I might come to the conclusion that I had no parents after all, but that will not make it the case that there are metaphysically possible worlds in which I had no parents—this is a matter of the facts about me, not my beliefs about the facts. Thus solipsism is an epistemic possibility but not a metaphysical possibility. It is just like the table being both necessarily made of wood (metaphysical) and also being possibly not made of wood (epistemic). Giventhat I arose from biological parents, I necessarily did; but it is an epistemic possibility that I did not so arise—I could be mistaken about this.

It would be nice to disprove solipsism, but it isn’t insignificant to show that it is not in fact logically possible, given the actual nature of persons. Persons are the kind of thing that implies the existence of other things (granted that we are right in our commonsense view of what a person is). In this they resemble many ordinary biological and physical entities, which also have non-contingent origins. We may feel ourselves to be removed from the world that surrounds us, as if we are self-standing individuals, ontologically autonomous—as if our essential nature could subsist alone in the world. But that is a mistake—we are more dependent on other things than we are prone to suppose. We are more enmeshed in what lies outside of us than we imagine. We suffer from illusions of transcendence and autonomy. We are not free-floating egos that owe no allegiance to anything else; we are essentially relational beings, our identity bound up in our history. We cannot be metaphysically detached from our origins, proximate and remote.

The same point applies to our mental states: they too cannot be separated from other things. Could this pain exist in complete isolation? That may seem like a logical possibility, but on reflection it is not: first, this pain’s identity depends on its bearer—it could not be thispain unless it had thatbearer; and second, the identity of the bearer depends on the kind of history it has. So this pain could not exist without the generative sequence that gave rise to its bearer, a particular living organism; and that depends upon billions of years of history, going back to the big bang (and before). There is no possible world in which this painexists and certain remote physical occurrences don’t exist. There are necessary links connecting present mental states with remote physical occurrences—from the joining of a particular sperm and egg, to the origin of mammals, to the production of chemical elements. My pains can’t exist in a world without me (you can’t have mypains), but I can’t exist in a world without my parents, and my parents can’t exist in a world without their remote primate ancestors, and these ancestors too had their own necessary origins. The pains that now occur on planet Earth (thosepains) could not exist in a possible world without an elaborate biological and physical history that coincides with their actual history.

It is an interesting fact that we recognize these necessities. On the one hand, we have quite strongly Cartesian intuitions about the person and the mind, which is why dualism and solipsism appeal to us—these seemlike logical possibilities. But on the other hand, we are willing to accept that the person and mind are tied to other entities with bonds of necessity—as with the necessity of personal origin. We recognize that the identity of a person cannot be radically detached from all extrinsic and bodily things—parents, sperms, and eggs. These are anti-Cartesian intuitions insofar as they dispute the self-subsistence of the self.[1]We are thus both Cartesian and anti-Cartesian in our modal instincts about persons. It is as if we know quite well that the self cannot be a self-subsistent non-material substance without logical ties to anything beyond itself, even though in certain moods we fall prey to such thoughts. We know that our essence implies the existence of other things—as demonstrated by the necessity of origin—and therefore solipsism is not in fact logically possible. We are modally ambivalent about self and mind, but not confused.


Colin McGinn

[1]Kripke mentions the anti-Cartesian consequences of the necessity of origin at the very end of Naming and Necessity(footnote 77, p. 155). What is surprising is that neither he nor anyone else seems to have noticed the consequences for solipsism (including myself, and I published an article on the necessity of origin in 1976). But it is really just a fairly obvious deduction from the necessity of origin (originally proposed by Sprigge in 1962, as Kripke notes).


The Mind-World Nexus


The Mind-World Nexus



According to a dominant tradition, appearances are not “in” objects: that is, how an object appears is not (completely) determined by its objective properties but depends on the mode of sensibility employed to perceive it.  The classic example is color: objects are not colored independently of how they seem but in virtue of the color sensations they elicit in perceivers. Thus we can conceive of variations of color without an intrinsic variation in the object but merely in virtue of being differently perceived (Martians may see as green what we see as red). Color is then relative to a type of perceiver—and not just perceived color but actual color. An object isred if and only if it seemsred to a suitable group of perceivers. We could put this point by saying that color is extrinsic to objects; it depends on what kind of perceiver exists in the object’s environment. If the environment contains one kind of perceiver (humans), then it is red; but if it contains contains another type of perceiver (Martians), then it is green. The color depends on context—on how the object is hooked up to experience. It would be wrong to think that color is internalto objects, as if objects could have determinate colors no matter how they are perceived. And much the same can be said of other sensible qualities associated with hearing, touch, smell and taste. Perhaps it is true that not all apparent qualities are thus subjective, such as shape and size, but many are. As is often said, such qualities are projected by the mind, generated from within, and spread on objects. They depend on the “psychological environment” of the object (no perceivers, no qualities).

I have put the point by using terms drawn from another debate, namely the debate between internalism and externalism about the mind. It is claimed that what kind of mental state a person has is dependent on his or her environment and is not a result of purely internal factors.[1]We can vary a person’s environment while keeping her internal states the same (Twin Earth cases), and when we do so we find that mental states track the environment. So mental states are extrinsically fixed (in part anyway) and environmentally sensitive. They are not “in” the subject—not locally supervenient, not a matter of internal facts. They depend on the physical context, on how the person is hooked up to his environment. So there is an abstract analogy between certain views of color and certain views of mental states: both are regarded as relational and context-dependent. In the slogan, mental states are not “in the head”, but neither are sensible qualities “in the object”. The mental world is not independent of the physical world, and the physical world is not independent of the mental world. The subjective embeds the objective, and the objective embeds the subjective. Thus mind and world are mixed together, each incorporating the other, each flowing into the other. It is not that the whole being of the mind is sealed off from the environment, but neither is the whole being of the external world sealed off from the mind. The world contains projected properties, and the mind contains introjected properties. The mind shapes the world (in part), and the world shapes the mind (also in part). So there is no fundamental dualism here: the world is partly formed by the mind, while the mind is partly formed by the world. When you are aware of external objects you are aware of your own mental contribution to their appearance, but equally when you are aware of your mental states you are aware of the world’s contribution to them. The mind absorbs and projects; the world also “absorbs” and “projects” (it “absorbs” color and “projects” mental content). Mind and world work together to produce a reality of colored objects and content-bearing mental states (though I don’t suppose there is any teleology coming from the world). In other terminology, the mind externalizescolor and internalizescontent—as we might say (metaphorically) that the world “internalizes” color and “externalizes” content. Mind and world are mirror images of each other, abstractly considered.

In fact, we shouldn’t really be speaking any longer of mind and world, as if there is an exclusive dichotomy, since each is woven into the other: there are traces of mind in the perceived world and there are traces of the world in the formations of the mind. What we have is a mind-world nexus: a joining, a merging, an overlapping. What we call “the world” is not purely objective in nature, and what we call “the mind” is not purely subjective in nature. The mind is (partly) constituted by the world, while the world is (partly) constituted by the mind: properties drawn from one side of this divide are found located on the other side. The world I perceive is partly internal to me (i.e. projected), and the mind I introspect is partly external to me (not “in my head”). From the point of view of objects (not that they have one), the colors (etc.) they wear are donated from the outside, while they provide their own service by constituting the mental content of subjects. Fancifully, we might view this arrangement as a quid pro quo: give me your colors and I will give you content in return. More soberly, the mind has two capacities: the capacity to absorb (internalize) and the capacity to project (externalize). It employs external properties to form its conceptual landscape, and it draws on its own resources to confer perceptible properties on things (it is useful to see objects as colored, etc.).

This is not to say that there is no mind-independent external world, or that there is no world-independent mental reality. On the contrary, I would strongly deny both assertions.[2]It is only to say that the livedworld is infused with both—both the world of external objects and the world of inner perception and thought. This is quite consistent with allowing that there is another level of description under which objects have purely internal properties (call it physics) and a level of description under which minds also have purely internal properties (call it narrow psychology). We don’t in physics describe objects in terms of mind-dependent qualities, and we don’t in narrow psychology advert to environmentally fixed psychological kinds. Color doesn’t affect the motion of bodies and they can exist without it; similarly, the operations of mind can be characterized without reliance on wide content and minds can exist without such content. For the purposes of science, we could accept that the two worlds don’t overlap; and it would certainly be quite wrong to conclude that either idealism or materialism is true given the considerations advanced so far (not everything about the world is contributed by the mind and not everything about the mind is contributed by the world). Rather, the phenomenalworld—both mental and external—the world we directly experience—thatworld is a mixture of mental and physical. The world I seeis partly made up of projected properties, and the mind with which I am directly acquaintedis up to its neck in externalities (e.g. my concept water). There are two levels of description here: one is inherently dualistic and the other is not. The one that is not concerns the world that we commonly occupy—the world that we sense, feel, talk about, and take for granted (which includes the mind). The other world is largely theoretical, which is not to say any less real. Think manifest image and scientific image.

I want to point out how remarkable the aforementioned capacities of mind actually are. When the mind internalizes an external property it converts that property from being a feature of external objects to being a vehicle of thought—and these are completely different roles. The property becomes bound up with a concept, and a concept has all sorts of distinctive properties–notably being a constituent of thoughts. This is a brand new career for the property and not one for which it had any prior training. Once it is a constituent of a proposition, it is required to participate in logical reasoning as well as mental representation of states of affairs. What has water (the H2O stuff) got to do with that, or being square or being arthritic? How does the mind perform this conversion operation—repurposing a property to start a new life as a concept? Externalists never answer this question—they just point to examples that (purport to) establish the doctrine. But it is really very puzzling: for how can a feature of the environment enter the mind in such a way as to shape its operations? What is this internalizationthat we speak of? How, for example, is the property of being square made to function as a constituent of perceptual experience and of thought? Not by making the mind square! It seems to undergo a metamorphosis, but the mechanism of this metamorphosis is obscure at best and impossible at worst. It might even make one to give up on externalism completely. Likewise, we speak blithely of projection, but how is thissupposed to work? It is not that the mind literally throws color at objects! Nor does it secrete color onto objects. No, the operation is purely mental—an operation of spreadingin Hume’s metaphor. This is both unhelpful and positively misleading. How does the mind externalize color, when it is not colored itself? How does it generate the qualities projected? How does the projected quality always manage to hit its target, painting the leaves green and the roses red with such precision? Somehow the brain produces an impression of a single object that has both color and shape, exactly coordinated, but it is not supposed that shape is projected; so how does it manage to project one quality and introject the other? Projecting color seems like a magic power—quite unlike what a film projector does (here there is actual transmission of light waves). All we have are vague metaphors but no theoretical understanding. This doesn’t mean that the mind doesn’t perform the action in question; it only means that we don’t understand how. In other words, the projective and introjective powers of mind are a mystery. Yet they are fundamental to our entire view of things.

Look at how perception must operate second by second. At a given moment a state of affairs presents itself to the senses—say, a red bird 10 feet in front of your eyes. Your visual sense must internalize this scene, its various properties and arrangements. The scene must so imprint itself that a suitable percept is formed that can then function as input to behavior: this is a highly complex conversion process whose workings are still poorly understood. But at the same time the brain must carry out a projection operation that bestows color on the seen objects, which is rapidly updated over time. It must take in but it must also give out. These operations have to be coordinated and unified. The stimulus for color projection just consists of impinging light rays in which no color is to be found; on reception of these rays the brain must issue an instruction to retrieve a certain color impression, which must then be combined with various shape impressions. The input is not colored but the output is. How the brain does this is a mystery. We know that the cones of the retina must be involved, but how the nervous system contrives to generate and project color is unknown except in gross outline. The result is that the perceiver sees a colored object, where the existence of the color depends on the existence of perceivers to project it. So there is a continuous interplay between internalizing and externalizing operations, tightly intertwined. It is not that perception is all internalization, as very naive naïve realism might suggest; but nor is it all projection, as idealism might maintain. The world is contributing to the mind and the mind is contributing to the world. In this two-way nexus we find the world as it is lived. We internalize the world (hence psychological externalism) and we externalize the mind (hence color subjectivism). Thus mind and world become intermingled.[3]


Colin M

[1]I won’t defend externalism here or even fuss over formulation; neither will I defend the subjectivist view of color. I am more concerned with their implications when conjoined. I defend externalism in Mental Content(1989) and subjectivism in The Subjective View(1983).

[2]I would count myself a staunch externalist andinternalist about the mind, and a staunch subjectivist andobjectivist about objects of perception. The key is to make distinctions between types of property or fact.

[3]Much the same can be said of language and meaning: semantic externalism brings the world into meaning and hence involves internalization, but the structure of language also shapes our view of reality, since our concepts are bound up with the structures of language (verbs and nouns, objects and properties). We need not accept the extreme view that our entire conception of reality is fixed by our language, which can vary from speaker to speaker, in order to recognize that language can function in a projective manner, imposing its internal architecture on our view of things. Language takes in but it also reaches out—it spreads itself onto perceived reality. Thus grammar can function like color perception. Then too, there is Freudian projection, in which traits of oneself are projected onto others, while the mind also introjects authority figures like parents. It seems that the mind is fond of the introjection-projection dialectic.


Al Franken

I just read the recent article in the New Yorker about Al Franken by Jane Mayer (July 29, 2019). It is a model of responsible journalism and lays the facts out admirably. He should clearly not have been forced to resign. It reminded me of when I met him in 2013 at George Soros’s wedding (though I had met him briefly a few years before at my gym in New York just after George W. Bush “won” the presidency for the second time). I told him my favorite Soros joke: “What is the difference between a Hungarian and a Romanian? They will both sell you their mother, but the Hungarian will deliver”. Franken said he thought it was a good joke. Now he has had his life destroyed.


Modularity and the Self



Modularity and the Self



We don’t always speak with one voice. We disagree with ourselves. The senses may say one thing while we say another. The classic case is visual illusion: the visual system may represent the world in a certain way, but reason says otherwise. The encapsulated visual module delivers an output that the central cognitive system contradicts.[1]There is internal dissent, discord in the ranks. One part of us says one thing while another part denies it. This can be global as well as local. Suppose someone arrives at the conclusion, on philosophical and scientific grounds, that ordinary material objects are neither solid nor colored: no matter how strongly held, this conviction will not alter how things visually seem. So the disagreement will persist indefinitely: the subject will disagree with his own senses. The same is true even for the belief that one is a brain in a vat seeing nothing: perception will keep on representing the world as if the subject were surrounded by objects of a familiar type. Perception is oblivious and impervious. If we think of perceptual outputs as assertive acts, then the visual system is saying “objects are solid and colored” or “I am really seeing external objects”, while the forces of reason are asserting the contrary. It is not common usage to report the senses as believing what they represent, but there is certainly something belief-likeabout what they do—they are committedto a certain view of things. They are not merely suppositional, as the imagination is; they make definite claims—as that objects are solid and colored and are really there. To say, “My visual sense believes that the two lines are unequal” while in the grip of the Muller-Lyer illusion is not wide of the mark—maybe it is even true unconsciously. Imay not be conscious of this belief, but my visual system might hold to it; in any case, it doesn’t seriously misrepresent the facts to say so. We might then describe the situation as follows: the senses believe that pbut reason (the central system) believes that not-p. Intrapersonal disagreement mirrors interpersonal disagreement. Cognitively speaking, we are at war with ourselves. The senses can’t bring us round to their point of view, but neither can we get them to accept ours. There is a split in our world-view: that is, our cognitive modules are not aligned.[2]

I put the point this way in order to accentuate a question, namely: Where is the self in all this? So far I have spoken of one module thinking one thing and another module thinking another, but this is not how we speak. I say, “My senses think (assert, believe, represent) that the lines are unequal, but Ithink they are equal”. So I seem to be supposing that one of my modules is more closely aligned with my self than the other: I merely havesenses, but I amwhatever it is that issues considered judgments. So my senses think one thing while I (my self) think another. The picture is that there is a supervisory self that evaluates what its several modules assert. And Ican reject what theyassert. They are something other than me, but I am not. Given that reason is what makes such judgments possible, it looks as if I am identical to reason: reason is what I refer to when I say “I”—not the senses. I might say, “My senses are misleading me badly” but not, “My reason is misleading me badly”—for that would be equivalent to saying that Iam misleading me badly. The senses are behaving like other people in relation to me, but I could not behave like another person in relation to me. At any rate, that is how we appear to conceive of ourselves: we privilege one module (faculty, capacity) over another in these internal disagreements, aligning it more closely with the self (maybe even identifying the two).

But what is the rationale for this? Why this aristocracy of reason? What if we inverted the privilege, asserting that I think the lines are unequal while my reason thinks they are equal? What if I preferred to link “I” to the senses not the intellect? What if I thought the soul resides in the senses not in the rational faculties?  We do have the locution, “I see the lines as unequal” as well as, “My visual sense tells me the lines are unequal”; so it might seem arbitrary to assign seeing to sense organs and thinking to the self, instead of assigning thinking to the rational faculty and seeing to the self. What if we simply adopted an organ theory of psychological ontology in which the self is no sort of additional entity? The sense organs give one sort of informational output while the central system gives another sort, with neither assigned preferentially to the self? The two organs disagree, but there is no selfthat takes sides in the disagreement: it is just reason versus sense, with no self in view. If we keep the word “I” in the picture, it seems that it can apply both to the senses and to reason—as in, “My reason tells me that not-pbut I see that p”. Why exactly do we talk as if I think but my eyes see? Descartes doesn’t say, “My reason thinks, therefore it exists”; and there is a long tradition of regarding reason as constitutive of the self. But it seems okay to say that my eyes (and brain) do the seeing—Isee only derivatively. This is why we so readily say that our eyes are deceiving us, but not that our reason is. The organ of sense is intuitively not a candidate for identity with oneself, while the organ of thought is. The central system is closer to methan the peripheral systems. Or so we tend to suppose. But why is this?

I raise this question in a spirit of puzzlement. A no-self theory removes the puzzle because there isno self to attach to a given mental organ—there are just ways of talking using “I”. It is not that reason is identical to the self and the other organs of mind lie outside the boundaries of the self (its little helpers, as it were); there is just the faculty of reason coexisting with the other faculties of the mind. The mind is a federation not a monarchy. But that is a drastic position, and one that flies in the face of common sense (but not to be dogmatically dismissed). The weaker position is that there is no difference between sense and reason in respect of the self—the self belongs to each equally. This too is a bit of a strain: we really do think that our senses tell us things and that we may or may not heed them. We listen to our senses, but we don’t regard them asus. The central system of belief formation is what does the listening; it is where Iam. If there were no such system, there would be no I: but you can lose your senses and still exist. The problem is that internal disagreement puts a wedge between one part of the mind and another part, and the self has to fall on one or the other side of this divide; but why it falls as it intuitively does remains obscure (hence the appeal of the no-self position). My senses relate to me as other people relate to me—as sources of information with which I may disagree—so they are regarded as distinct from me. But it is harder to think of reason that way: it is not like an external informant with whom I can sensibly dispute. For what could that be if not my faculty of reason itself? And a bare transcendent self has no opinions with which to contradict other opinions. So the self aligns itself with reason as against sense—a very Cartesian position.[3]Yet the matter remains obscure.


[1]I am assuming Fodor’s position in Modularity of Mind(1983).

[2]The case of dreams is peculiar: dream content can certainly contradict what we believe when not dreaming, but it isn’t like perceptual illusion. It isn’t cut off from what we think in the way the senses are. It lies midway between sense and reason (rational thought). We might describe it as “semi-encapsulated”. Memory and the unconscious raise similar issues.

[3]The Cartesian might claim that thought essentially links to the immaterial ego while perception links to material sense organs; thisis why we talk as we do. That would be a kind of metaphysical reification of what must have a less startling explanation. And we know that “I” is a very funny word.


The Inefficacy of Skepticism




The Inefficacy of Skepticism



There is something peculiar about skepticism, psychologically speaking. It seems both cogent and ineffectual. Our epistemic practices are roundly criticized, convincingly so, and yet we decline to modify them; we soldier on regardless. We don’t refute the skeptic, but we don’t heed him either. Why are we so complacent, stubborn, and irrational? We are like flat-earth true believers who know all the refutations of their position but cling to it anyway. Of course, there are those who seek, by a variety of stratagems, to blunt the force of skepticism, thus bolstering their initial naïve epistemology; but this always reeks of cognitive dissonance, and is generally unpersuasive. And there are many others who reject such soothing stances and yet still decline to alter their epistemological assumptions—what is it with them? Skepticism thus retains both its power and its impotence: hard to rebut, but also hard to go along with.

We can imagine that not being so. Suppose some possible beings develop the kind of commonsense epistemology possessed by normal humans—the usual concepts of belief, knowledge, justification, reason, evidence, etc., along with the usual distribution of these concepts. They believe, and take themselves to know, various truths about their environment, other minds, the past, the future, etc. But also suppose that at the very outset skepticism starts to rear its head—it comes with the territory. Skeptical possibilities become widely entertained, and not just in university departments. Children start to bring them up, spontaneously and nervously, around the age of ten after a few blissful years of epistemological complacency. People quickly realize there is something seriously amiss with their assumptions. It is rather like starting life with superstitious beliefs and then soon discovering science. We would expect some major revisions of opinion, on pain of irrationality. Maybe some diehards will try to cling to their earlier views, but most will capitulate to reason, accepting that they are really notcertain that there is a table there, or that they are not brains in a vat, or that other people have minds. They might well also agree that such beliefs are not even adequately justified and are not genuine instances of knowledge. They accordingly cease to talk and think this way—as people outgrow superstition, religious dogma, and prejudiced politics. Skepticism is given its due; earlier opinion is discarded. One can be brought up to believe the tenets of a particular religion, but it is within one’s power to abandon those tenets under cogent criticism—and so it might be for one’s “epistemological religion”. And it is not as if you will go to hell if you discard your callow epistemological dogmas.

Or consider this possibility: a group of beings holds to commonsense epistemology for thousands of years with nary a skeptical thought among them. No one has so much as thought of skepticism, so there isn’t any pressure for revision. Children never wonder about what colors other people see, or ask if it’s all a dream, or how we know that the future will resemble the past. Then a particular individual, call her Helena, through some quirk of genius, comes up with skeptical arguments, which (we are supposing) are thoroughly convincing. Helena publishes these arguments in a scientific journal and they reach the public via global press coverage (think Einstein on relativity). Headline: Scientist Discovers We Don’t Know Anything. It is conceivable that our beings will accept the findings in question, as people have accepted other earth-shattering discoveries (species evolved by natural selection, the earth moves, we are not the center of the universe, slavery is wrong). They thus revise their epistemic belief system to fit the new ideas, declining to throw around words like “certain”, “know”, and “justified” with the abandon of yore. It becomes part of received opinion that these words don’t apply as widely as was believed heretofore, maybe applying only to one’s knowledge of one’s own mental state. So late-onset skepticism could have the same efficacy as early-onset skepticism; the mere fact of arriving late on the scene doesn’t imply that skepticism must be resisted. It is just that epistemic error has been around for a very long time. So why don’t we fit either of these models?

It is an empirical question when skepticism first arose for humans. We can safely assume that it wasn’t coeval with the onset of epistemic concepts and their associated beliefs: humans didn’t discover skepticism at the precise moment they began to deploy epistemic concepts, or a short time thereafter. We know that skepticism was much discussed in ancient Greece, but that must post-date by thousands of years the existence of commonsense epistemology. So we would expect some inertia about abandoning this aspect of ordinary belief. But such inertia didn’t stop other ancient canards from going extinct. Would humans have found it easier to let skepticism have its way if it had cropped up later in history, as in my second scenario? It might be argued that skepticism has grown stale for us and thus has lost its initial sharp edge; if it had been discovered at the time of the scientific revolution, it might have had more potency. But this seems implausible: it would still have encountered stiff resistance if discovered in 1680 or 1952. Why? It is conceptually possible for there to be beings who accept its urgings, so why are we so intransigent? It would be different if the skeptical arguments were simply fallacies and follies, easily defeated and defanged, but (we are assuming) that is not so. So what is going on here? Why are we so internally divided on the subject, schizoid almost? Why do we accept the force of skepticism and yet do nothing about it, even when we are quite self-conscious about our position? Why the psychological split?

I have a theory. Consider perceptual illusions such as the Muller-Lyer illusion: these are products of our epistemic faculties—they purport to represent aspects of the world, inviting belief, and offering justification (i.e., how things seem). Yet they are false: those lines are not really unequal in length. The perceiver need not know this and so may form the belief that the lines are not equal. This counts as a piece of commonsense perceptual epistemology. We can imagine people being under this illusion for centuries, never realizing that it is an illusion. Or consider the moon illusion: people might really believe that the moon shrinks as it rises over the horizon into the night sky. Now some scientist points out that these are indeed illusions—things seem that way but they are not really that way. Some people may persist in their earlier beliefs in the face of compelling evidence to the contrary, but most will come to accept that they were wrong—they have been under an illusion. But there is no corresponding change in their perceptual responses: it still looksto everyone as if the lines are unequal and that the moon shrinks. The perceptual system is not penetrable by outside information; it is “encapsulated”.[1]It is modular, stimulus-dependent, and bottom-up. No amount of reasoning, no matter how cogent, can prevent this system from mechanically delivering its standard output. It is, we might say, impervious to reason—a kind of reflex that we have to live with even when we know it is leading us astray. You might have very good reasons for suppressing your patellar reflex, but find it impossible to do, given the way your nervous system is wired; well, the visual system is like that, sublimely indifferent to higher rationality. From this we may infer causal isolation: central beliefs cannot cause the visual module to vary in its mode of response. Such beliefs are quite inefficacious when it comes to controlling vision. So we evidently contain two sorts of informational system that are insensitive to each other (the visual system can’t usurp the central cognitive system either). We thus arrive at a dual-system epistemic psychology. The two systems function autonomously, have a different ontogenesis, and may even employ distinct sorts of mental representation; no doubt they also have different neural substrates. They co-exist and can interact but they don’t mingle—one has no veto power over the other. Sometimes they hardly seem to communicate with each other. We might say that the visual system inclines one to believe what its output (a visual impression) suggests, but this inclination doesn’t prevent one from fully accepting that the facts are otherwise. The result is an oddly ambivalent state of mind, which accounts for the fascination of such illusions: on the one hand, you are inclined to believe what your senses tell you, but on the other you firmly reject their intimations. If someone were to tell you that all this illusion stuff is just a hoax thought up by manipulative scientists—the lines really are unequal and the moon really does shrink—you would be tempted to respond, “I knew it all along!” It is hard to accept that your visual system, otherwise so reliable, should so cruelly deceive you—as if you have a little evil demon living inside your head. As it is, however, you conclude that the scientists are right and your visual sense is wrong—while all the while your senses stick to their own version of things. Theywill not be moved.

My theory, then, is this: our commonsense epistemic system is also an autonomous module separate from the system that trades in skeptical arguments. The commonsense system (“folk epistemology”) pre-dates the reflective skepticism-involving system and is largely independent of it. We started by describing ourselves using epistemic terms at some point in human evolution well before written language and sophisticated culture developed, probably as a result of an innate faculty, and only later did human thought begin to reflect upon itself and issue criticisms. Just so, human vision evolved before science and objective measurement, only later becoming subject to rational criticism, but unable to respond to such criticism by altering its mode of operation. Thus skepticism failed to penetrate the cognitive system that pre-existed it. Put simply, people reflexively apply epistemic concepts to themselves and others, but these applications are independent of higher-order reflection of the kind employed in skeptical arguments.[2]They are encapsulated, automatic, and hard-wired. It is as if we are under the illusionthat we know: that’s how we seemto each other. I seem to know many things about the external world, other minds, etc., but skepticism teaches me that this is an illusion, exposed by consideration of our true epistemic situation.[3]The hamster may be under a similar illusion and be equally impervious to skepticism (if the hamster could understand skepticism)—precisely because it is programmed to accept its natural perspective on things. We go around the world representing it (wrongly, I am assuming) as containing knowledge, justification, certainty, and evidence, by courtesy of our innate epistemic endowment; but skepticism can make no inroads into this system, despite its superior wisdom, because the system is encapsulated and largely oblivious.[4]Thus we have a dual epistemic architecture: a primitive quasi-reflexive uncritical system, and a more sophisticated reflective critical system. The former is reluctant to take orders from the latter, as an adolescent doesn’t listen to his elders and betters. These faculties have different developmental schedules and neural implementations, and they might even differ in their coding properties and mode of operation. It would be possible to have the former without the latter, as presumably children are for some time in this condition. This would explain our divided epistemic self, our ambivalence, our schizoid tendencies, and our confusion. The commonsense faculty is a lot more ancient and primitive, a holdover from simpler times (and look how much illusion and error has been alleged by contemporary science!); the skeptical line of thought is something superadded, a product of late human culture, by no means integral to what preceded it.[5]No wonder it has so little impact on its set-in-its-ways predecessor! But we mixed-up humans contain both systems and so have to live with their quarrels: we are aware of what we are inclined naturally to think andof what our reflective reason says about those inclinations. We want to attribute knowledge, but we are cognizant that this attribution is questionable. We are caught between these two judgments—as we are caught between the conflicting claims of perception and cognition. This is why skepticism is psychologically peculiar: in it we are witness to our own psychological plurality—the fact that we are an assembly not a unity. We suffer from internal conflicts, no doubt with an evolutionary basis. Our faculties don’t always fit harmoniously together. This is a familiar thought for our emotional nature, but the same is true of our cognitive nature, as the case of perceptual illusion so vividly illustrates. I have suggested that our attitude to skepticism has similar roots. One faculty tells us that we know; another says not so fast. The former persists in its ways despite the superior wisdom of the latter.



[1]I am here following Jerry Fodor inModularity of Mind(1983).

[2]Here we may be reminded of Hume’s famous response to the skeptic: we can believe skepticism in our study but we lapse back into common sense when we leave it. Thus we have “natural beliefs” and “philosophical beliefs”—each the province of different cognitive faculties. (Contemporary cognitive science is in many ways a reversion to seventeenth and eighteenth century thought.)

[3]To repeat, I am assuming the cogency of skepticism here, not arguing for it; my question is what explains our reluctance, or inability, to take it seriously in our ordinary practices.

[4]The same might be said of the problem of free will: first we believe in it as a result of an ancient cognitive-cum-affective system, then we come to question it because of scientific ideas such as determinism and genetics. Even when convinced we have a tendency to cleave to old ways—thus we can find ourselves both disbelieving in free will and yet unable to shed our commitment to it.

[5]Psychologists have postulated a “theory of mind” module that grows spontaneously in the young child, much as the language faculty does; it is quite unhindered by skeptical thoughts concerning other minds. Those thoughts come later and from a different source (“critical reason”): they make little dent in the earlier module. Thus we automatically view others as having minds, even though we may be intellectually convinced that we have no grounds for this supposition. Similarly, we have a “theory of world” module that pre-dates and resists later skeptical reflections, however unreasonably. If we put the point in terms of organ psychology, it is as if the primitive mental organ keeps pumping out what it is designed to pump out even when the organ of rational thought counsels otherwise. After all, evolution has only a passing interest in objective truth; what matters to the genes is what works (which may, or may not, coincide with the truth). Whether anyone reallyknows anything, or has justified certainty, is not a matter of great concern to evolution.


Ideas of Time

Ideas of Time



It is well known that Einstein was influenced by Hume and Mach (who was also influenced by Hume). In particular, his treatment of simultaneity was influenced by Hume’s discussion of ideas of time in the Treatise. So it might be useful to revisit that discussion to see how well it holds up under scrutiny. Not surprisingly, Hume applies his general theory of ideas to ideas of time, particularly duration: he maintains that our ideas of time derive from our impressions of time. How we conceive time is fixed by how we perceive time. The concept “copies” the percept. Thus we read: “The idea of time, being derived from the succession of our perceptions of every kind, ideas as well as impressions, and impressions of reflection as well as sensation, will afford us an instance of an abstract idea, which comprehends a still greater variety than that of space, and yet is represented in the fancy by some particular individual idea of a determinate quantity and quality”. He asserts: “Nor is it possible for time alone ever to make its appearance, or to be taken notice of by the mind”. Accordingly, “wherever we have no successive perceptions, we have no notion of time”, so that time can only be “discovered by some perceivablesuccession of changeable objects”. Again: “The idea of duration is always derived from a succession of changeable objects, and can never be conveyed to the mind by anything steadfast and unchangeable”. So the idea of duration is always and necessarily that of a perceivable succession of changes in objects and cannot arise without such perceptions. This, as Hume points out, directly follows from his copy theory of ideas, given that we only have impressions of succession not of pure duration. As he says, we have impressions of time only in the form of relations between events—ordering relations. We perceive time passing byperceiving change occurring. So our concept of time is just the concept of such change. For example, we see physical changes in clocks and thereby infer that time is passing: there is no more to our concept of time than what we observe inside and outside.

It is easy to see how this conception of temporal concepts could lead to radical conclusions about simultaneity. If the concept of simultaneity arises purely from impressions of simultaneity, it will turn out to be relative, since what seems simultaneous to one observer will not seem so to another; this is evident from such simple cases as the time lag between impressions of lightning and impressions of thunder, which varies with distance. The concept of absolute simultaneity thus turns out to be meaningless under Hume’s theory of ideas once we take different observers into account. The same is true of duration, since different perceivers will have different rates of perceived succession.  In fact, Hume operates with two principles in the Treatise: the copy principle and the principle that what is not contained in an idea so derived is empty. It follows from both together that time itself must conform to our impressions of it—it has no nature independent of such impressions. We thus reach the conclusion that there cannot beduration without the perception of change—the thing itself not just the idea of it. Starkly stated, there is nothing more to time that how it seems to us in perception, for we have no conception of it independently of our perception-derived ideas. Given this philosophy of time, it is not surprising that Einstein motivates and justifies his conception of time by reflecting on the observation of clocks, since these afford our empirical basis for thinking about time. Anything else would violate Hume’s empiricist strictures. Newton’s absolute conception certainly does, since it corresponds to nothing in our experience—no one has ever had an impression of an absolute infinite time independent of change. As Hume says, summing up his position: “The ideas of space and time are therefore no separate or distinct ideas, but merely those of the manner or order, in which objects exist”. It is thus “impossible to conceive either a vacuum and extension without matter, or a time, when there was no succession or change in any real existence”. It is a short step from this to Einstein’s ideas about the relativity of simultaneity and the corollaries he draws from that.

The trouble is that this is all immensely dubious. I will merely list the many objections that have been and can be made against Hume’s theory of ideas. First, there was the missing shade of blue, a straight counterexample to his copy theory. Second, ideas are singular and abstract whereas impressions always include many qualities and are concrete. Third, animals have impressions but don’t generally have corresponding ideas, so the step to concepts cannot consist in an impression leaving a mark in memory. Fourth, elements of images in the imagination are not functionally identical to concepts. Fifth and connected, concepts join together to form propositional thoughts, but impressions don’t (or copies of them): concepts compose but impressions merely co-exist or succeed. Sixth, even images are not really copiesof impressions but have a nature of their own, differing in many ways from impressions.[1]Seventh, Hume relies heavily on the argument that he can think of no other theory of the origin of ideas, but this argument is weak. What about the rationalist theory of innate ideas? What about the theory that ideas are linked more to language than to perception, corresponding to the word-like elements of the lexicon (plausibly regarded as innate)? What about the possibility that we just don’t know the origin of ideas? Better to accept ignorance than push a manifestly inadequate theory. Eighth, what justifies the inference from ideas to reality? Just because our ideas can only have a certain sort of content, why does it follow that reality must reflect this content and contain no more? Isn’t that idealism? Ninth, as Hume recognizes, the very existence of the standard debates about space and time apparently shows that we do have ideas of absolute space and time; it is just that we are arguing about which theory is true.[2]Don’t I have the concept of other minds even though my impression of other minds is purely of the bodily behavior of others? I know quite well what I am talking about; I just don’t know whether other minds really exist. Tenth, concepts are nothing like memories, which they would be if Hume’s theory were correct (they don’t fade or mutate like memories). Eleventh, Hume often conflates ideas of things with ideas of impressions, but most of our ideas are not of impressions: I have an idea of a square thing, but this is not the idea of an impressionof a square thing. The latter idea seems like a reasonable consequence of having an impression, but why should the former be so derived? That would be moving quite beyond the impression itself. Finally, a concept does not present itself to introspection as impression-like: it is far more elusive, hidden, and obscure. We can’t just introspect and report what a concept is, as Hume seems to assume. The theory of concepts is actually quite undeveloped and highly controversial, with Hume’s empiricist theory just one theory among others; it lacks the self-evidence he cheerfully takes it to have.[3]

So Einstein’s reliance on Hume was reliance on a very frail reed—indeed, I would say, a complete non-starter. If this was his basis for rejecting classical notions of time and promoting his own radically revisionary opinions, then it was totally wrongheaded. Humean concept empiricism is not a sound foundation for constructing a theory of the physical world. Nor do I see how Einstein’s arguments for the relativity of simultaneity can survive without such reliance, as inspection of his writings reveals (the Hume-inspired positivism is quite apparent). One is inclined to conclude that bad philosophy leads to bad physics. Certainly, Einstein’s physical theory derives no support from the underlying philosophy of time. It looks as if a false philosophical theory of ideas has led to a bizarre physics full of paradox and puzzlement. The question is whether it is possible to detach STR from the erroneous philosophy that led to it. I can’t see how, but I am no physicist.[4]


Colin McGin

[1]See my book Mindsight: Image, Dream, Meaning(2004).

[2]Consider this remarkable passage: “If it be a sufficient proof, that we have the idea of a vacuum, because we dispute and reason concerning it; we must for the same reason have the idea of time without any changeable existence; since there is no subject of dispute more frequent and common. But that we really have no such idea, is certain. For whence should it be derived? Does it arise from an impression of sensation or reflection? Point it out distinctly to us, that we may know its nature and qualities. But if you cannot point out any such impression, you may be certain you are mistaken, when you imagine you have any such idea”. Hume’s hectoring use of italics here does nothing to bolster the entirely question-begging character of his rhetorical questions. On the face of it, the existence of the disputes in question provides a simple proof of the falsity of his theory of ideas: how can we be certainwe lack certain ideas when for all the world we are discoursing about them? A rationalist, say, would be unimpressed with Hume’s confidence. What is certain is that we have the ideaof such ideas!

[3]I do agree that Hume’s theory is apt to make an impression on impressionable young minds (if the puns be excused), and he is no doubt a formidable polemicist; but really his empiricist theory of ideas (concepts) is grossly implausible. I wonder whether the young Einstein knew other philosophers’ work as well, particularly the rationalist tradition. He would not be the first or last young person to fall under Hume’s spell. (By the time of the EnquiryHume himself had seen through his earlier exaggerations and doesn’t revisit the topic of time.)

[4]The influence of logical positivism on physics was, and still is, considerable, and it can be difficult to disentangle this influence from purely empirical considerations.


Physiology of Mind



Physiology of Mind


Physiology lacks a philosophy to call its own. There is no philosophy of physiology to speak of. Perhaps this is because physiology is a sub-discipline of biology and we already have a philosophy of biology. But this neglects the possibility that physiology works with concepts and theoretical constructions specific to itself, and these require philosophical treatment in their own right. Here is how the OEDdefines “physiology”: “the branch of biology concerned with the normal functions of living organisms and their parts”. As always, this definition is worth dwelling on. Physiology is the science of the functioning of living organisms and their component parts, such as the heart, the kidneys, and the brain. The word “function” here has two separate connotations: it refers to theoperationsof organisms and their parts, and it refers to the purposeof those operations. How do organisms work and why do they work that way? Thus the function (purpose) of the heart is to circulate blood, and the way this purpose is achieved is by acting as a pump with a certain structure and mode of action. Physiology must first identify the end an organ serves and then explain how that end is achieved by the organ in question. And what is an organ? The OEDhas this: “a part of an organism which is typically self-contained and has a specific vital function”. An organ is relatively autonomous in its operation and its function is specific and vital (though not necessarily a matter of life and death). So physiology is concerned with organs that have their own identity and which have a dedicated specific purpose not shared by other organs. The central concepts of physiology are therefore life, purpose, functioning,andorgan.Notice that no restriction is made to the body as opposed to the mind (this will be relevant later), nor are genetics and evolution invoked.

Venturing beyond the dictionary definition, we can make a number of other observations about physiology (the science and the reality). First, there is a division of labor among organs: some do one job and some do another (nineteenth century physiologists compared the body to a factory). Second, function and structure are intimately connected: whatever the function of an organ is, it must have a structure that suits it to perform that function; and physiology as a science must characterize this relation. We may think of it as a fittingrelation: it resembles the way artifacts fit their function—they must be physically capable of performing it. Thus physiology (functioning, activity) must dovetail with anatomy (structure, architecture). Third, although organs are sharply differentiated, they must be integrated—because they have to work harmoniously together. Rogue organs do nobody any good. They need some sort of central command or supervision (here is where the brain comes in handy). Fourth, and connected, organs belong to organ systems, forming complex organs—consider all the organs that go into digestive systems. These must be integrated together, but they also need to be integrated with other organ systems. Accordingly, there is a hierarchical structure to physiology: systems, subsystems, individual organs, components of such organs, etc. Fifth, there is a normative aspect to physiology: that is, we have the notions of health and disease, normality and pathology. This is because of the teleological element: organs are healthy or defective according as they achieve their purpose, which is to preserve life (which we assume is a good thing). Sixth, just as the organism exists in an external environment which it must negotiate, so the several organs of the body exist in an internal environment; and in both cases adjustment and accommodation are required. Here is where homeostasis comes in—the need to keep the internal environment stable and contained within certain limits (temperature being the most obvious parameter). The organism exists in a physical environment and one that contains other organisms; the organs exist in a chemical environment and one that contains other organs. There is a nesting of environments. The organism has a certain Umwelt, but so does the individual organ. This point gives rise to the seventh observation: organs, like organisms, are input-output devices. Something goes in and something comes out. Often the organs function as a conversion device—as with the lungs and stomach. All organs need nutrients to be absorbed in order for actions and processes to be powered. The components of the body are not isolated and cut off. Thus the organs need to contain interactive mechanisms—devices that make things happen, often of elaborate design. The system is intricate and interlocked, though differentiated and distinct. Eighth, the organs have a genetic basis, a distinctive embryogenesis, and an evolutionary history; they are certainly not “acquired” by means of interaction with the environment. The tabula rasais a very bad model for physiology. The heart is as hard-wired and pre-determined as any nativist could wish. Ninth, despite the manifest variety of organs, there are certain physiological universals, particularly pertaining to cellular structure: all organs are made of cells, though the cells typically differ histologically. Thus macro-physiology is highly heterogeneous, while micro-physiology is quite homogeneous (the cell with its nucleus, membrane, and mitochondria). As it were, the atoms are alike, but the objects they compose exhibit considerable variety, according to their specific jobs. Tenth, we can, for any organism, make a list of its characteristic organ systems, which serve to fix its phenotype; these may overlap with other species or may be unique to the species in question. By my reckoning, human physiology contains the following organ systems: digestive, respiratory, sexual, circulatory, immune, motor, postural, sensory, protective, and mental (with many subdivisions: see below). So the magic number is 10—other species may well have less, though in general this number seems to apply to all but the simplest organisms. Thus evolution needed to produce 10 organ types that work together to keep an organism alive. Subtract any of them and you tend to get a dead organism. Physics and chemistry have their types of particle; physiology has its types of organ. The raison d’etreof each is its contribution to maintaining life.

Before I turn to applying this conception to the mind, it will help to talk in some detail about specific organs, so that we have a concrete point of comparison. The heart is composed of two types of cell, known as cardiomyocytes and pacemaker cells, which have different functions. The former enable muscular contraction and are cylindrical in shape. They have high mitochondrial density that enables them to produce large amounts of ATP, which makes the heart resistant to fatigue. Heartbeats are caused by the shortening and lengthening of fibers. The gross anatomy of the heart divides it into the atria and the ventricles, chambers that receive blood and pump it out, respectively. The tissue of the heart is a type of muscle tissue. By pumping blood the heart serves its purpose of circulating blood throughout the body to maintain organs and perform other functions. The functioning of the heart is closely linked to the respiratory system. The kidneys, for their part, have a different shape (more like a large bean) and are made up of different cell types called nephrons. They process liquids and expel urine. The liver is a large organ that contains hepatocytes and endothelial cells, boasts two lobes, is adjoined to the gallbladder, and performs a variety of functions related to digestion, also secreting bile. Diagrams of these organs can be made and they have a distinctive macro anatomy and microanatomy. Structure is suited to function; function is specific; there is input and output; there are links to other organs. This is the stuff of physiology as defined above. It goes beyond more general biological concepts, such as genotype and phenotype, natural selection, species, evolution, reproduction, and so on. Physiology is primarily concerned with the concept of an organ, understood in the way outlined—structure, role, purpose, operation. As remarked, this concept is not conceptually tied to the body or to the concept of the physical: it could have turned out that organisms house non-corporeal organs (as was supposed for the elan vital), so long as these entities fulfill the general abstract definition of an organ. If cavities in the body perform a role analogous to meaty tissue, then they too would count as organs, since they aid life. Or a Cartesian biologist might postulate an immaterial organ responsible for circulating the blood, on the (mistaken) assumption that such an impressive and important feat could not be performed by mere matter and needs the help of the ethereal. Most significantly for our purposes, nothing in the definition of physiology requires that the mindnot count as an organ possessed by an organism. Hence we have the idea of a physiology of mind—a science of mental organs.[1]That is, psychology is a branch of physiology. Not just a branch of biology, but a branch of the branch of biology called physiology. Nor is this conception in any way precluded by the etymology of the word “physiology”, since this word derives from a Greek word meaning simply “nature”. Nothing specifically physicalis entailed (whatever exactly “physical” is supposed to mean).[2]

The basic idea is far from novel (Chomsky has been speaking of “mental organs” for decades and comparing them to bodily organs). What I want to do is apply the conception developed above in an explicit theoretical way, so that the mind emerges as fully and properly physiological–not metaphorically but literally. The mind really is an aspect of the physiological constitution of the organism, animal or human. It is literally a collection of physiological organs. Recall the dictionary definition of “physiology”: “the branch of biology concerned with the normal function of living organisms and their parts”. Surely it is obvious that the mind of an organism is part of its normal function: the mind has a function and this function is normal. Or rather, the mind is made up of faculties (“organs”) that have a function and which function in the life of the organism. The sense experiences of bats, say, have a function and they function in the life of a bat—they have a purpose, a nature, and a mode of operation. We refer to the senses as sense organsfor a reason—they literally are organs. But they are not purely bodily organs—they are psychophysical organs; they have both a mental and physical aspect. Their having the former aspect in no way disqualifies them for the title “organ”. Not that it matters whether the word “organ” fits as a matter of common usage; from a theoretical point of view, vision (say) is as much a vital biological property of an organism as the stomach. There is no principled or interesting dividing line here. Animals have organs in their bodies and they have organs in their minds (or partly so). Again, the dictionary definition of “organ” confirms this topic-neutrality: an organ is just part of an organism that is “self-contained and has a specific vital function”. It would be pointless to quibble over the word “part” here on the grounds that mental faculties are not really partsof an organism; we could easily rephrase the definition by using “aspect” or “property” or “trait”. The interesting question is to what extent mental organs share the characteristics I attributed to organs in general, for that is what determines whether the concept of the physiological is apt. So: is the mind organ-like?

Consider the language faculty. There is much controversy on this subject but I propose to cut through all that and adopt a specific perspective, roughly that developed by Chomsky. I will accordingly say that language is an internal system (with an external expression) that consists of rules of computation and a lexicon of word-like elements. A grammar specifies the structure of this system and takes a generative form. The grammar is innate and modular. Sentence structure can be represented by tree diagrams. The grammar outputs infinitely many possible strings on a finite basis. The internal system connects to sensory systems (typically hearing) and to motor systems (typically speech mechanisms), as well as to cognitive processes such as logical reasoning. Given this general conception, it seems evident that the language faculty counts as an organ and hence as an element of human physiology. It has a complex internal structure, relatively specific, with connections to other mental organs, an innate basis, and even its own mode of depiction (those tree diagrams). If we ask what its function is in the life of the organism, the answer is not far to seek: it serves either as an aid to thought or as a means of communication (depending on your view of the purpose of human language). In either case (or in both) language performs a vital biological function in the life of the human organism; you are at a comparative disadvantage without it. It contributes to reproductive fitness. It propagates the genes. It is also an input-output system: sensory inputs, including speech, and motor outputs, also vocal (sometimes gestural). You report what you see and hear and you talk about what you think and feel. So it is connected to other organs or modules or faculties, and hence operates in its own specific internal environment (consider internal speech). It is differentiated yet integrated, self-contained yet embedded. Thus it counts as part of human physiology—our nature as living things, our phenotypic identity. Essentially, it has a certain functional architecture that fits into the life of a particular species—a compositional structure and characteristic mode of operation. As plants engage in photosynthesis as part of their mode of living, so humans engage in linguistic synthesis as part of their mode of living: they put sentences together by following certain procedures and this product aids them in life. And this faculty can exhibit signs of ill health and disease if it fails in its purpose, as other organs can: thus aphasia and the various types of language pathology. The language faculty is not supposedto issue in nonsense or grammatical error, yet it sometimes does—it is then not working according to its function. There is right and wrong, good and bad, well-formed and ill-formed. Physiology is inherently vulnerable to breakdown and malfunction, and language is no different. This is a logical consequence of having a biological purpose.

Much the same can be said about other commonsense mental categories: perception obviously, but also memory and reasoning. I won’t discuss these in detail; it is fairly easy to see how the story will go. There will be a specification of the organ’s function and a description of its enabling structure–the former obvious, the latter less so. Then we will need to locate it in a wider system, characterizing its inputs and outputs, and its internal environment. There will be specific architectural details, as well as some shared properties (constituent structure looks like a universal). We might be able to draw a map of the mind relating its various components—a full mental anatomy.[3]No doubt there will exist a physical and chemical basis to the mental organs at a deeper level of analysis (which will not replace the higher levels), and a cellular substrate. The important point is that we are not now engaged on a completely different enterprise from that of traditional physiology; we are merely extending that enterprise. The same theoretical framework is employed, but now applied to the physiology of mind.[4]A stubborn residual dualism will be resisted in favor of a more unified vision of the organism. The mind will be granted a lot more internal structure than on certain traditional conceptions, which insist on a radical discontinuity between the study of the body and the study of the mind (the body jammed with structure, the mind merely a blank nothingness). The body turned out to have a lot more internal structure than early physiological inquirers suspected; the mind will likely reveal a lot more structure than similarly benighted theorists assume (and has already done so). Framing the questions in physiological terms provides an apparatus for inquiry that encourages the same kind of open-minded exploration. Approaching an alien species, we would expect to discover its internal bodily organization—its organs and their processes—but we should adopt the same attitude towards its mental organization. The most basic principle of physiology, whether of the body or the mind, is that nature has made organisms to consist of differentiated but integrated organs serving specific functions. There is no such thing as blank and homogeneous physiology.[5]


[1]Kant speaks of the “physiology of understanding” in relation to Locke’s project in the Essay: this was a good insight on his part. See the preface to Critique of Pure Reason.

[2]The physiological conception I am advocating is not to be confused with the perspective of so-called neuroscience. There is nothing reductionist about my proposal and its preferred descriptive vocabulary is not the same as that of the brain sciences. That vocabulary is geared to the type of cell composing the brain (neurons) as well as the gross anatomy of the brain. By contrast, the vocabulary of physiology abstracts from this detail and talks of organs, function, structure, life, and organic systems. This talk is topic-neutral and in no way presupposes a “physicalist” view of the mind (whatever that might be).

[3]It is an interesting question whether consciousness counts as an organ in its own right or whether it is a quality possessed by various mental organs. I suspect the latter to be true, but in either case it would be a physiological phenomenon, perhaps analogous to the smoothness of bodily organs, which is shared by many such organs.

[4]Let me put in a word for the “second brain”, that neural structure in the gut that regulates digestion. Assuming that there are mental correlates to its operations, we could postulate a “second mind” that harbors its own set of mental organs (see my “The Second Mind”, in Philosophical Provocations, 2017). I suspect many people will be more ready to grant physiological status to this lowly mind than to the more familiar mind that engages in logical reasoning and artistic creativity. But really the “head mind” is no less organic than the “gut mind”.

[5]Even a physiology of an immaterial Cartesian substance, if such there could be, would deal in organs and their activities, since the mind is made of a number of interacting faculties that need an operational structure. The immaterial mind would not be a formless nothing any more than the body is. Perception, thinking, language, memory, emotion, and volition will all require specific configurations of the immaterial stuff in which the mind is held to reside. And there will be the same questions about purpose, mode of operation, etc.