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.
 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.