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Are We Bodies or Souls?
by richard swinburne
oxford, 208 pages, $19.95

In the history of Western thought, two conceptions of the soul have competed for dominance, one associated with Plato and the other with Aristotle. For the Platonist, your soul is the real you, and your body merely a vehicle to which it is temporarily attached—indeed, your body is a kind of prison from which the soul needs to be liberated. For the Aristotelian, by contrast, our bodies are no less essential to us than our souls are. Only soul and body ­together make a complete person.

Descartes adopted something like Plato’s view, though his Catholicism prevented him from treating the body as a prison. He argued that the causal connection between soul and body is so intimate that it is misleading to think of the latter as a mere vehicle. Still, like Plato, he regarded soul and body as two distinct substances, each a complete entity in its own right and only contingently associated with the other. This Platonic-Cartesian position is known as substance dualism.

Thomas Aquinas rejected this position in favor of Aristotle’s view that a human being is one substance, albeit a substance with both bodily and non-bodily activities. Walking, talking, seeing, hearing, digesting, and so on are all bodily. Thinking and willing are immaterial or non-bodily. But it is the same substance that does all these things. Because some of what we do is non-bodily, the death of the body is not the extinction of the person. The postmortem soul is essentially the human being reduced to his intellect and will. But death is not a liberation. It is a radical diminution, which is why the realization of our ultimate destiny requires the resurrection of the body. This Aristotelian-Thomistic conception of human nature is sometimes known as Thomistic dualism.

In his latest book, Are We Bodies or Souls?, philosopher Richard ­Swinburne defends the ­Cartesian form of dualism and criticizes the Thomistic version. An emeritus professor at the University of Oxford, Swinburne is one of the great Christian apologists of the age. His method, implemented in a series of volumes published over fifty years, has been to deploy his vast knowledge of contemporary analytic philosophy in a rigorous defense of various theological claims concerning the existence of God, the possibility of miracles, the doctrine of the Trinity, the resurrection of Christ, and so on.

Swinburne offers two lines of argument for the reality of an ­immaterial soul. One of them, inspired by ­Descartes, appeals to the thesis that it is conceivable that I could continue to exist as a thinking thing even if my body were destroyed. From this it follows, in Swinburne’s view, that I am a substance whose entire essence is the capacity to think, with the body being inessential. Otherwise, my continuing to think beyond the death of the body should not be even conceivable.

Naturally, there is more to the argument than this, and Swinburne shows that the objections raised by some contemporary philosophers are too glib. All the same, I do not think the argument works. Arguing from what is conceivable for a thing to the essence of the thing simply gets things the wrong way around. In fact, you need first to know the essence of a thing in order to be able to judge that what seems to be conceivable for it really is conceivable, and not just a cognitive illusion. Hence, only if I could independently show that thinking is immaterial, and thus not essentially dependent on the body, could I know that it really is conceivable for me to continue to exist as a thinking thing beyond the destruction of my body. But in that case, I would already have established the soul’s ­immateriality, and the appeal to conceivability would be doing no work.

Swinburne’s other argument appeals to the failure of reductionist accounts of the self. Some philosophers argue that the persistence of the self over time is merely the persistence of certain bodily traits over time. Others argue that it has to do with the ­continuity over time of memories and perhaps personality traits. Still others argue for some combination of these criteria. Swinburne argues, quite correctly in my view, that all such accounts face counterexamples. For example, suppose a person’s brain is divided in half and each half is placed in some new body, with each of the resulting persons having bodily traits, personality traits, and memories that are continuous with the original person. In this case, the two new persons cannot both be identical with the original person, because then they would have to be identical with each other, which they are not. Hence there must be more to the continuity of the self over time than merely the continuity of certain bodily or psychological traits.

Swinburne concludes that what accounts for the continuity of the self over time must be an immaterial soul. But that does not follow. For one thing, some reductionists would argue that if we cannot reduce the self to a collection of physical or psychological traits, then so much the worse for the self. It must be an illusion. I don’t for a moment think that this position can be made coherent, but Swinburne does not address it.

For another thing, even granting that the self exists and is irreducible to a collection of bodily or psychological traits, it does not necessarily follow that the self is immaterial. Thomists, following Aristotle, typically hold that vegetative life is irreducible to inorganic processes, and that animal forms of life are irreducible to vegetative forms of life. All the same, plants and animals are entirely material substances. So, to show that there is an im­material soul (as Thomists agree there is), ­Swinburne must do more than merely show that the self is irreducible.

The second general difficulty with Swinburne’s position is that he fails adequately to deal with the “interaction problem” that notoriously faces Cartesian dualism. To be sure, he argues at length that soul and body truly interact causally with each other. But the interaction problem has to do with explaining how this is possible. The most serious difficulty is that, given the Platonic-Cartesian view that soul and body are two entirely distinct substances related only contingently, it is hard to see how Swinburne can account for the unity with our bodies that we experience. The Cartesian soul’s relation to the body seems comparable instead to a poltergeist’s relation to a radio it switches on or a vacuum cleaner it pushes around the room. It is a “ghost in the machine,” as the British philosopher Gilbert Ryle famously described Descartes’s view of human nature. Swinburne’s position makes the body something like a piece of property of which you are the proprietor, rather than something you truly inhabit.

Nor are Swinburne’s criticisms of the Thomistic account of the relation between soul and body effective. For one thing, he mischaracterizes the view. Aquinas, as Swinburne correctly notes, did not regard the postmortem soul as a “complete substance.” But he mistakenly infers from this that Aquinas regards soul and body as two substances, each of an incomplete kind. And he concludes that Aquinas’s view is therefore essentially the same as Descartes’s—that mind and body are distinct substances—only stated in a misleading way.

But this is a travesty of Aquinas’s position. If I eat and completely digest half of an apple, the remaining half is an incomplete substance, but it doesn’t follow that the half I ate is also an incomplete substance. Rather, it is altogether gone. Furthermore, even if it were not gone—suppose I cut the apple in half and placed the two halves side by side—it wouldn’t follow that there are two substances there, albeit incomplete ones. Rather, there would be two halves of one substance.

Similarly, for Aquinas, a human being is one substance, not two. When the body dies, the intellect and will carry on, and this residue of the human being is what the postmortem soul consists in. Because a human being is a substance, this residue of a human being—having lost all of its bodily operations—is an incomplete substance. But that doesn’t mean that the body is a separate substance. For one thing, it is gone (like the digested half of the apple). For another thing, even if it were not gone, it would not be a different substance from the soul, but rather a different and separated part of the same one substance.

Swinburne appears to think that Aquinas is guilty of inconsistency insofar as Aquinas says that persons no longer exist when they lose their bodies, while also attributing to the postmortem soul activities characteristic of persons, such as willing and praying. For surely if souls are doing such things, then the persons whose souls they are can be said to be doing them. Swinburne seems not to be aware that many Thomists would agree with him that souls can do such things only if there is a sense in which they are persons, albeit incomplete persons. They would say that, when denying that postmortem souls are persons, what Aquinas intended was merely to reject the Platonist view that the body is something inessential to the person. This is called the “survivalist” interpretation of Aquinas’s position. There is an alternative “corruptionist” interpretation, which is indeed open to Swinburne’s criticism. It holds that a person flatly ceases to exist at death, as opposed to ­continuing to exist but in an incomplete way. But there is nothing in Aquinas’s basic premises that requires a Thomist to adopt this corruptionist view.

All that said, Thomists would agree with Swinburne that human beings are not entirely bodily, and that the immateriality of the mind can be established via philosophical arguments (albeit arguments very different from those Swinburne favors). And one can only admire the erudition, philosophical acumen, and fair-mindedness with which he defends his position. Swinburne is in that class of thinkers from whom one always learns much, even when one ends up having to disagree.

Edward Feser is professor of philosophy at Pasadena City College.