Other Bodies

The orthodox view of our knowledge of minds is that while other people’s minds are doubtful my own mind is not: I can be certain of my mind but not of other minds. Hence there is a skeptical problem of other minds but not of my own mind. There is a deep epistemological asymmetry between self and other. However, it is not thought that there is a comparable asymmetry with respect to the body: the existence of other bodies is doubtful, but so is the existence of my body. I might be a brain in a vat with no body, and other people’s bodies might be hallucinations; there is a skeptical problem about both. Now that I don’t contest, but it doesn’t follow that there is no epistemological difference between my knowledge of my body and my knowledge of other bodies. I could be more certain of my body than I am of other bodies, and the ground of my knowledge might be different in the two cases. So, let’s explore the question. How do I know other bodies (human, animal, and inanimate)? I know them by sense perception, notably vision. But sense perception is subject to illusion and hallucination, so that source of error has to be recognized. How do I know my own body? By sense perception, to be sure, but also by direct knowledge of what I am doing, by proprioception, and by sensation (feelings in my body). So, I have more evidence about my body than I have about other bodies—more to go on, more to appeal to. Moreover, I don’t have hallucinations of my own body as I have hallucinations of other bodies—I never have impressions of my body existing when it does not, as I have impressions of other bodies existing when they do not (as when I have a false impression of someone lurking in the dark, etc.). Also, I am always (when awake) aware of the condition of my body, even when I can’t perceive it with my five senses, but this is not true of other bodies. I can’t have proprioception of other bodies, but proprioception of my own body is ever-present and highly reliable. All in all, I am in a solid position epistemologically with respect to my body: I know my own body remarkably well, even if I can’t be certain I’m not a brain in a vat. It’s really the best-known physical object in the world as far as I am concerned. I would venture to suggest that the probability of my body existing is a good deal higher than the probability that other bodies exist. I am more ready to accept body solipsism than the hypothesis that other bodies exist but mine doesn’t. I’m pretty damn sure my body exists! Yours, well, that’s more a matter of speculation, faith, received wisdom. Every night I dream of bodies that don’t exist, but I never dream of my own non-existent body. But is this something I can defend against a determined skeptic? Actually, no, except to a limited degree, but this degree marks a difference between my body and yours. For I can argue that I must at least have a brain, while your brain is up for grabs. This is because I know with certainty that I have a mind, and my mind needs a brain; but I don’t know with certainty that you have a mind, so I can’t infer from that that you must have a brain. I can’t move from knowledge of your mind to the conclusion that it is housed in a brain, because I don’t have that knowledge; but in my case, I have indubitable knowledge of my mind, so I have a solid basis for the move to a brain. Thus, I have a Cogito-type argument for a body part belonging to me, but I have nothing comparable in your case—you could be all hallucination as far as I am concerned (though not as far as you are concerned). There is no Cogito-type argument of the form “I think, therefore you have a body”, but there is such an argument as “I think, therefore I have a body”—where the body I have perhaps consists just of a brain. Can I infer the existence of any bodies other than my own from the existence of my body (even if that is just a brain)? In the case of the mind, that looks to be infeasible: I can’t infer from the existence of my mind that any other minds exist or ever existed or will exist (solipsism-of-the-moment is inescapable as a skeptical possibility). But in the case of the body the prospect of other bodies looks brighter: because I can infer from the existence of my body that other bodies didand will exist. The reason is that the matter of my body did once belong to another body and it will later come to belong to a separate body too. The matter of my body moves around composing different bodies at different times, but the “matter” of my mind does not. Thus, my bodily matter survives my body’s demise, as it once survived the demise of another body or bodies; but my mind does not likewise persist through time—it is limited to me. So, I can know that other bodies once existed and will exist, given that I know that I have a body—not so for mind. This thinking thing might be the only thinking thing that ever existed or will exist, but this extended thing is one among many extended things spread out in time—that is its nature. I can assert “I am an extended thing, therefore there must be other extended things (at some time)”, assuming that a past and future exist during which my matter exists and my body doesn’t. My body implies other bodies (on reasonable assumptions) but my mind doesn’t imply other minds; and this point applies equally to my brain alone. (But, of course, I can’t infer that your body exists in this way, since your body is not composed of the matter that composes mine.) In short, I know more about my body than I know about your body; so, I have more of an other-body problem than a my-body problem (though I do have somewhat of a my-body problem). It is true that I cannot be certain that I have a body just as I experience it, but I can be certain that I have some sort of body (even if it’s just a brain quite unlike the one I think I have). However, I really can’t be certain that you have a body of any kind, since you might just be a figment of my imagination, an outright hallucination. Accordingly, it is too simple to say that there is no epistemological asymmetry between my knowledge of my body and my knowledge of your body: I am better placed to know my own body, and in several ways.[1]

[1] In the Matrix people hallucinate their body and are quite wrong about what it is up to, but they can’t hallucinate the fact that they have some sort of body, since that is a precondition of their having a mind at all. But there is no conceptual bar to hallucinating other people’s bodies in toto; they need not have any physical reality at all.

Cogito for the External World

The traditional Cogito “I think, therefore I am” yields a moderate harvest of existential conclusions: the existence of a subject of thoughts (albeit momentary and etiolated) and the existence of propositions as the content of thoughts. We might compare this to a plant that is rooted in the earth and directed to the sun (earth as subject, sun as proposition). The plant exists, as it were, between the earth and the sun—as a thought exists between a subject and a proposition. It needs both, pointing down and pointing up; it “presupposes” earth and sun, as a thought presupposes subject and proposition. But does the thought (episode of thinking) bring with it any further existential implications? The plant also exists in a surrounding environment of physical objects and processes—does the thinking exist in a surrounding environment of objects and processes? If so, are these objects and processes logically implied by the thinking? In particular, is what we call the external world implied by the existence of thoughts? Is there a Cogito for the external world? The idea might seem incredible: how could a thought, an event of thinking, imply the existence of the external world? What about the evil demon and the brain in a vat? True, some philosophers have sought to deny that these scenarios are really possible—they have held that the content of thought requires the existence of suitable external objects in order to exist at all. Thus, we have “externalism” about the content of thought: what a person thinks is fixed by his or her actual environment and causal connections thereto. However, such views are not terribly plausible; in any case, I won’t discuss them. But I will discuss another line of argument that seeks to forge a logical link between mind and world—between the internal and the external. That is, I will defend the following Cogito: “I think, therefore the external world exists”; or, to parallel the traditional phraseology, “I think, therefore it is”—in Latin “Cogito, ergo est”. The “it” here is the physical world that exists outside the mind—the world of extended objects in space. We won’t get the entire external world as normally conceived, but we may get a part of it—and so derive from “I think” propositions concerning the existence of ordinary material objects. The first thing to notice is that thoughts (and other mental events) do in fact occur in an environment of physical objects, rather like plants; the question is whether this is an a priori necessary truth. Thus, thoughts occur in the vicinity of bodies and brains and interact with these objects, as a matter of actual fact; what we have to determine is whether this is built into the very identity of thoughts, a necessary condition of their existence (like subjects and propositions). Is it part of the nature of thoughts to be so situated? First, we can observe that thoughts have bodily effects: what you think affects what you do. And this is part of their identity: if you think it’s cold, you will dress warmly (given appropriate desires). If a thought did not have such consequences, it would not be thatthought. This is a familiar reflection. Of course, the thought might not actually have such consequences, but it is (as we say) disposed to have them (even if the brain of the thinker has been removed from the body, he still has a tendency to act in certain ways). The question is what this tells us about the thought itself: must it be somehow bodily? I think the answer is yes: the thought can have bodily effects only because it has a (partly) bodily nature. That is, the thought can only have a certain functional role vis-à-vis the body if it has a (partly) bodily nature. This nature will involve the brain; so, the thought has a cerebral nature of some sort. A materialist will say that its nature is wholly cerebral, but we need not commit ourselves to that, restricting ourselves to the weaker claim that it has a cerebral aspect. Accordingly, and in line with reasonable materialist sympathies, thoughts must have a physical nature of some sort (along with a possibly non-physical nature). But then we can deduce from the occurrence of a thought that something physical exists—that there exists something bodily that is built into the thought. This something is presumably complex and consists of elements that could exist without the thought existing (just like in the case of the brain), so we get the idea of a material world that can exist independently of anything mental. We get something like an atomic theory (bodies are made up of smaller physical components). Of course, we already know this to be true on empirical grounds, but now we see that it is deducible a priori from the very nature of thinking: if a thought exists, it must have a nature that allows it to affect the body (if there is one); but then it must have a bodily nature of its own; therefore, there must be something bodily in the world. Cogito, ergo est. I think, therefore there is an external world. Given that I know with certainty that an episode of thinking is occurring, and given that I know a priorithat this requires bodily existence of some sort, I can infer that a body exists in much the way I normally suppose. In fact, I can be certain of this—or as certain as I am that subjects and propositions exist given that thoughts do. I can infer a physical “environment” for acts of thinking much like the one I normally take for granted (centering on the brain). I can formulate a Cogito for the external world, or part of it.[1] Lichtenberg is thus multiply wrong in his claim that nothing follows from “I think” apart from the existence of thoughts. And Descartes is wrong that the Cogito argument applies only to the self; in fact, the conclusion is more robust in the case of the external world than in the case of the self, since only a vanishingly thin notion of self can be derived from “I think”. Descartes, of course, cannot avail himself of this argument for the external world given his dualism—for him the mind has no physical nature at all—but this dualism is hardly something we would wish to hang onto. A reasonable dose of materialism is all we need to develop a modified Cogito that delivers substantive conclusions about the make-up of the world: we can now assert that the world is partly mental and partly physical. The existence of physical things follows from the existence of mental things; it isn’t merely a contingent add-on. Thus, thoughts are rooted in selves, point to propositions, and incorporate their physical environment (the brain). They imply the existence of something psychological (a self), something abstract (a proposition), and something physical (a body); they are not logically cut off from the rest of reality. They affirm more than just their own existence (a la Lichtenberg) but extend outwards into three domains. The Cogito has been underestimated.[2]

[1] I won’t discuss how much of an inroad into skepticism this makes except to say, “Some but not much”.

[2] It has been overestimated in its original incarnation, as a proof of the existence of the self as commonsensically conceived; but it has been underestimated as a device for proving other existential propositions from apparently minimal resources. There is more in “I think” than meets the eye.

Do I Know That I Exist?

I am going to argue (a) that the Cogito cannot prove that I exist but (b) that it can prove that various other things exist. This is ironic given that it is commonly supposed that the Cogito can establish the existence of the self (person, subject) but that only the self’s existence permits of such a demonstration. Both these points are actually quite easy to establish, as it turns out. In order to know whether the Cogito can prove the existence of the self, we need to know what the self is. So: what am I? That is a philosophical question—a question of metaphysics—and there are several answers to it that have been proposed. These are: the self is an animal body; the self is a composite of a body and a mind; the self is just a mind (“conscious subject”) and nothing more; the self is a primitive entity that can be described both mentally and physically. It is clear that three of these views will not permit the deduction of the self from the premise “I think”. For we cannot deduce from that premise that a body exists: that is subject to Cartesian doubt and is not entailed by the mere existence of thought (but see below). Nor did Descartes suppose otherwise: he didn’t think he could deduce the existence of any extended substance, such as a human body, from the premise that he thinks. So, if any of these bodily views is correct, the Cogito is powerless to demonstrate the existence of the self so understood. No, what Descartes supposed is that the Cogito can prove the existence of the self as a purely mental thing (a “res cogitans”). So, what is this purely mental self? Clearly, it is the subject of mental attributes: not just the attribute of thinking but also of desiring, intending, imagining, feeling, believing, and anything else you think belongs to the mind. But how can “I think” establish the existence of a subject that does these other things? How can we assert anything like “I think, therefore a subject of desire exists?” Thinking doesn’t entail desiring (imagining, etc.)! All that I can infer from “I think” is that a certain part of me exists—the part that thinks. But that is not all that I am qua conscious subject, so this multifaceted self is not demonstrable via the Cogito. In order to prove the existence of that self we will need separate arguments corresponding to each mental attribute: e.g., “I desire, therefore the desiring part of me exists”. But this doesn’t prove the existence of a unitary self—the self I take myself to be. It just proves the existence of many subjects of consciousness corresponding to each mental attribute I possess. But that is not what I am, i.e., a unitary being—unless we take the view that the self is actually not unitary but merely an assemblage of separate parts. The trouble with that view is that it is false: that is not what I am. So, the reconstructed Cogito does not deliver the self that actually exists, but only some watered-down conglomerate. Strictly, it only delivers a small part of the self as normally conceived—the part that thinks. The Cogito should read “I think, therefore a thinking thing exists”—with no implications for the existence of a self that thinks and desires and imagines, etc. But that is obviously not what the self is as we normally understand it, a thing that merely thinks. This is a thin surrogate for that familiar self. In fact, I know quite well that I am a unitary self with a variety of mental attributes; it is just that this knowledge is not vouchsafed by the Cogito. Indeed, the correct conception of the self is along the lines of “a single unitary embodied conscious subject enduring over time”: but the existence of that self is certainly not demonstrated by the Cogito. So, the Cogito does not establish the existence of the self—as it really actually is. At best it gives only an aspect or part of the actual real self. If I know that that self exists–and surely, I do know this–it is not by means of the Cogito; it might well be by means of ordinary observation, internal and external. Descartes wanted a skepticism-proof demonstration of the existence of the self, but he devised no such thing; the lesson should be that there is no skepticism-proof demonstration of the existence of the self, not as it normally (and correctly) understood. However, the Cogito can be used to prove the existence of other things, arguably important and surprising things; and thus, it provides a way out of solipsism and the mere existence of thoughts. Some of these are obvious, but some are not. First, it proves that there are mental attributes, since thinking is a mental attribute. I am certain that I am thinking (“there is thinking”), and I am certain that thinking is a mental attribute, so I am certain there are mental attributes. I am also certain that thinking is not a physical attribute, given that thoughts are not extended and extension is the essence of the physical. I also know with certainty that I know these things, since I can see that they follow logically from “I think”. Furthermore, I know that at least one token thought exists, and not just the type thought; so, I know that my thinking exists in time (token events need time to occur in, unlike types). In addition, I know that concepts exist, since thoughts are made up of them: there is no such thing concept-free thought. I also know that propositions exist, since thinking is a propositional attitude; so, I know that concepts combine into propositions. All this is obvious and easily deducible, but it doesn’t stop there. Don’t I also know with certainty that my acts of thinking are caused, given that all events have a cause? And if I know that, don’t I also know that my thoughts are governed by laws, given that causation implies laws? Thus, I can put together what I know by introspection with what I know a priori and derive some moderately interesting results. Some of these results have existential implications such as the existence of events and laws: thinking consists of token events with causes and causes require the existence of laws to back them. And now we might see our way clear to more surprising deductions: for example, that my thoughts must have a physical substrate. For, if events of thinking are subject to causal laws, but there are no causal laws of thinking per se, then these events must fall under other laws, and these would have to be physical (Davidson’s argument). If we combine this argument with the “I think” of the Cogito, we reach the conclusion that I have a brain! My point here is not to endorse that argument but merely to illustrate that there is room to get beyond the mental world that is demonstrated by the Cogito. We might also construct an argument establishing that space must exist if thoughts do, because time requires space, or because it makes no sense to postulate a world of individuated concrete events outside of space. We can thus work out from the Cogito to more adventurous conclusions aided by suitable a priori principles.[1] The certain knowledge that I think can be made to yield results independent of the traditional Cogito, which is dubious for the reasons given above. This procedure may not be skepticism-proof but it may be sufficient to generate knowledge of matters that transcend the mere awareness of thinking. The general idea behind the Cogito was essentially sound, although the traditional move to the existence of the self doesn’t work. If so, both Descartes and Lichtenberg were wrong: we can’t get the self from “I think” but neither is it true that we can get nothing but the existence of thoughts.

[1] I am not saying that this is easily done, or even that it is ultimately possible; I am merely saying that it is part of the intellectual landscape and not to be dismissed out of hand. It is a project worth pursuing.

The New Cogito

I think, therefore I am (not extended)

I think, therefore I am (made of two parts)

I think, therefore I am (not an animal)

I think, therefore I am (not getting out of bed today)

I think, therefore I am (never going to get married)

I think, therefore I am (not very popular)

I think, therefore I am (unemployable)

I think, therefore I am (no fun to be around)

I think, therefore I am (not going to get tenure)

I think, therefore I am (ill-coordinated)

I think, therefore I am (chronically constipated)

I think, therefore I am (not a university administrator)

I think, therefore I am (thought to be insane)

I think, therefore I am (at least a thing)