Could there be such a thing as reincarnation? A necessary condition would be the truth of some form of dualism. So far so good, since (I would say) some form of dualism is true. But which form? There are at least three to choose from: substance dualism, the version associated with Plato and Descartes; property dualism, associated with the likes of John Locke, David Chalmers, and (the early) Frank Jackson; and the hylemorphic dualism defended within the Aristotelian-Thomistic metaphysical tradition. Are all of these equally favorable to a defense of reincarnation?
Property dualism might seem adequate to do the trick, especially when conjoined with a Lockean account of personal identity. Locke holds that for some person existing after your death to count as the same person as you, it is sufficient that that person’s consciousness be continuous with yours in the sense of containing memories of having done the things you’ve done, manifesting your distinctive personality traits, and so forth. It is not necessary that there be any continuity between your body and his; he will still be you even if he has a completely different body. Nor is it even necessary that he have your soul in the sense of a Cartesian immaterial substance. All that matters, for Locke, is that your consciousness has somehow jumped from your current body to his future one, or even (if there are such things as Cartesian souls) from your current immaterial substance to his. Locke seems to think of mental characteristics like memories and personality traits as comparable to pieces of fruit which might be carried from one bowl to another – not only from one material “bowl” (a body) to another, but (at least in principle) from one immaterial “bowl” (a soul) to another. Though, since he appears to be a kind of property dualist (at least as a “working” position), it seems the “bowl” would in fact in his view be material and the “fruit” immaterial, surviving the death of one brain and landing safely in another. (Locke appears to be at best agnostic about substance dualism, opting instead for property dualism as a way of maintaining the immateriality of the mind in the face of the difficulties for the notion of substance his empiricism puts him into. See pp. 79-87 of Locke for discussion.)
This might seem to fit in well with the best evidence for reincarnation, viz. reports of individuals who appear to exhibit memories and personality traits of deceased people of whom, under the circumstances, they arguably could not have acquired knowledge via the normal means. For it seems that an incomplete assortment of memories and personality traits is typically all that such individuals are claimed to exhibit. That is to say, we don’t seem to have cases like (say) a 19-year-old female saying things like “I’m Jimmy Hoffa, and I can prove it! Go dig under the concession stand at Giants Stadium and you’ll find my previous body. Grab me a beer and brat while you’re at it” – acting and talking exactly like the deceased person and having the full complement of his memories, Heaven Can Wait style. Rather, the purported continuity between the living person and the dead one is at best fragmentary and ambiguous (as in a movie like Dead Again). If we think of memories and personality traits on the model of immaterial “fruit” spilling from the bodily “bowl” at death, it is no surprise if only some of it makes it into a single new “bowl.”
But in fact property dualism does not plausibly lend support to reincarnation. Consider that if memories, personality traits, and the like really are analogous to fruit that might persist independently of the brain, they can hardly be properties but must be something more like substances. For if they were properties (in the sense in which contemporary philosophers use the term “properties,” which roughly corresponds to the Scholastics’ term “accident” – the Scholastics use “property” to refer only to a “proper accident”), then they could not persist apart from the substance in which they inhere.
[Might the doctrine of transubstantiation be brought in to rescue a property dualist construal of reincarnation? For according to that doctrine, the accidents of bread and wine persist even though the substance of bread and the substance of wine have disappeared. But this will not help the property dualist construal of reincarnation, at least if we understand reincarnation in the usual way, viz. as resulting from the operation of the law of karma. For the law of karma is supposed to be an impersonal and natural law, which determines all by itself, and without the intervention of any divine being, that the soul of a deceased person will be reincarnated in a body of such-and-such a type. By contrast, as traditionally understood (and as required by Thomistic metaphysics) transubstantiation cannot occur in the natural course of things but requires a miraculous suspension of the natural order by God. In the natural course of things, accidents cannot exist apart from a substance.]
So, reincarnation is more plausibly defensible given substance dualism than given property dualism. (Locke’s conception of survival of death is not intended to require substance dualism, of course – indeed, it is intended to avoid the need to commit to substance dualism, or to any particular doctrine of substance for that matter. But it is hard to see how it can do so. If Locke’s “continuity of consciousness” theory of personal identity were correct, then the extinction of the substance in which your consciousness inheres would surely be your extinction, and any later person who seemed to have your memories and personality traits could only ever be a mere duplicate of you and not the McCoy.)
But here another problem arises. If reincarnation occurs via the migration of a Cartesian immaterial substance from one body to another, why don’t memories and personality traits persist in a more robust way, reappearing unambiguously and in their entirety in the new body? For unlike immaterial properties, a Cartesian immaterial substance is essentially ontologically independent of the body, even when it is conjoined with it. Hence it is hard to see why even the shock of the death of the body would so disorient it that its memories and personality traits reappear in only a fragmentary way. A “reincarnation hypothesis” put forward as an explanation even of the most impressive instances of individuals who purportedly exhibit memories and personality traits of deceased persons would thus seem hardly more plausible than alternative explanations – possession, say, or information received through unconscious telepathic means from living relatives of the deceased. These are bizarre proposals, of course, but so is reincarnation. The point is that even if we do not dismiss alleged cases of reincarnation as mere fraud, there are alternative explanations that are not obviously worse than the reincarnation hypothesis. Or at least, they are not obviously worse given that if substance dualism is true, it seems we should expect more complete and unambiguous continuity between the deceased person and the person in whom he has allegedly been reincarnated. (For a sympathetic and philosophically serious discussion of the most impressive cases and of various possible ways to interpret them, see Stephen Braude’s Immortal Remains: The Evidence for Life After Death.)
What a defense of reincarnation needs, then, is a version of dualism on which something like an immaterial substance survives the death of the body, but in such a fashion that we would naturally expect it to function in a far from optimal way after death, so that lapses in memory and the like would not be so surprising. And here it might seem that hylemorphic dualism would do the trick. For the hylemorphic dualist holds that the soul is the substantial form of the body, that capacities like sensation and imagination are material in nature, and that even strictly intellectual activity, which it takes to be immaterial, requires the aid of sensation and imagination. Hence it is not at all surprising – indeed, it is to be expected – that our mental activity is largely dependent on bodily processes, and that it should be severely impaired by the death of the body. (We have had reason to discuss these matters earlier, here and here.) But hylemorphic dualism also holds that the soul is a subsistent form, which persists beyond the death of the body as a kind of incomplete substance.
Tailor-made for a defense of reincarnation, right? Not so fast. For the hylemorphic dualist claims, not merely that your soul is the substantial form of a body, but that it is the form of a human body, and indeed the substantial form of your human body in particular. Hence it cannot even in principle inform the body of some other human being, much less the body of a non-human animal. Scenarios of the sort one finds in movies like Heaven Can Wait and Dead Again – and, for that matter, All of Me and Freaky Friday – are therefore ruled out as metaphysically impossible. (Awful luck for us movie fans, but there it is.) Also ruled out, naturally, are the man-to-brute reincarnation scenarios posited in some religious traditions. To be sure, hylemorphic dualism does allow for the possibility of your being reunited with your body via resurrection, which might count as a kind of “reincarnation.” But of course, that’s not what most people mean by the term.
But hylemorphic dualism is true, or so I would argue. (See chapter 4 of Aquinas.) Hence reincarnation in the sense in which it is understood in religions like Hinduism and Buddhism is (in my view) impossible. Therefore, alleged cases of reincarnation, if they are not simply fraudulent, must be explained in some other way.