Traditional dualism is characterized by two theses: (a) the mind is a separate substance (object, entity) from the brain, and (b) the mind is immaterial. These are logically independent; in particular, (a) does not entail (b). The mind could be a separate physical substance from the brain, existing alongside it. Or neither could be physical, since the concept of the “physical” is irredeemably ill defined, ever since mechanism was abandoned in the wake of Newton’s introduction of action-at-a-distance. Descartes believed both (a) and (b), holding that matter is defined by extension and mind by thought (which is not extended). But if we give up on that way of defining the difference between mind and body, we can assert that the mind is not identical with the brain (or body generally) and yet is not immaterial. Neither is the brain “physical” in any useful sense, since it harbors powers and forces not recognized by traditional materialist science (electromagnetism, notably). According to modern physics, the brain consists of fields and quantum states not hard little lumps of impenetrable matter. In any case, we are under no logical obligation to describe the brain as physical and the mind as non-physical, as if this reported anything of serious significance. The brain is a biological organ, to be sure, but so is the mind—whether identical to the brain or not. So it is logically open to us to maintain that the brain and the mind are separate things—separate biological organs—without getting caught up in the matter of immateriality. The important question is not whether one is “material” and the other “immaterial” but whether they are the same or not. That is the question of dualism (versus monism) not the question of whether the world contains any immaterial substances as well as material ones. This latter question we can happily discard as antiquated, while the former question can legitimately command our attention. If the mind is indeed a separate substance from the brain, it is available as the subject of psychological predications; it is not the brain that is the bearer of mental states but the mind. Or the self, if we prefer to speak that way: the self is the thing that thinks and feels, senses and acts. According to dualism, the self exists as a separate entity from the brain, i.e. the two are not numerically identical (this is compatible with certain kinds of dependence). We can say this without buying into some supposed dichotomy of the material and the immaterial: we can be dualists without being immaterialists. We just decline to talk in that style or, if we are wedded to it, we describe the mind as another sort of physical thing—rather as earlier physicists agreed to describe electromagnetism as physical even though it was of a different nature from what had hitherto been rated “physical”. The better question is whether there are minds or selves distinct from bodies and brains: are we composed of two sorts of thing or one?
And there are good reasons to return the answer two. For minds and selves are not individuated as bodies and brains are, as many thought experiments from the theory of personal identity show. Brains and minds have different identity conditions and don’t necessarily track each other over time or at a time: the brain can remain in existence while the mind perishes; a single mind can conceivably occupy different brains (by uploading or gradual replacement of parts); a person can survive the removal of half of his brain while brain itself is no longer fully intact; and so on. Brain and mind have different criteria of identity. The right thing to say here is that just as there are emergent properties so there are emergent objects: selves or minds are biologically emergent objects, stemming from brains no doubt, but not reducible to them. We need a robust ontology of such entities (get your quantifiers ready!) as well as the ontology of bodies and brains. If we ask what the nature of these extra entities is, we have a number of options: we can stick to appearances and declare their nature to be nothing other than what is supplied by our ordinary talk of the mental, or we can postulate a hidden nature the terms of which currently escape us. The latter alternative allows us to suppose that the second substance has a real essence (as Locke would say) that could in principle be discovered and investigated, analogous to the chemical structure of familiar substances. Maybe cognitive science is even now mapping this hidden terrain. In either case we need not be silent on the question of nature: the mind or self has a nature proper to it just as the brain and body do. It is just that these natures are different. Of course, there is interaction between the two, and a dependence of mind on brain, and an interlocking of function—but not numerical identity. The case is like the distinction between lungs and heart: not the same things but plenty of interplay.
To what extent do these separate entities share attributes? Here is one notable overlap: both are temporal. Brain processes take place in time, and so do mental processes. Both things are temporally extended (unlike abstract entities such as numbers). Descartes never denied that, merely insisting that the mind is not spatiallyextended. This is actually quite a concession, because it locates both mind and body in the same world of changing perishable phenomena—in nature, in one sense of that pliable term. And then there is the possibility that the temporal must have a foot in the spatial, if time and space have any necessary connection. In any case, the mind shares with the brain the attribute of temporal existence. What about spatial extension itself? The question is not straightforward: admittedly, the mind does not belong to phenomenal space—we don’t see it as thus extended—but it might nevertheless belong to noumenal space, whose nature may be capacious enough to include it. Maybe the mind is extended in this possibly unimaginable space—it takes up some of it. Certainly it exists cheek by jowl with spatially extended matter, so one might suppose that it cannot be quite removed from space; conceivably the two join together in a type of space that defies our ordinary conceptions. So, pace Descartes, we might allow that thought has a spatial aspect, even though we have no perception or conception of it. Actually I think this idea has a good deal to be said for it, but I won’t go into that now; it is enough to remark that the two substances could resemble each other in point of space and time while still being genuinely distinct. This would be quite different from classic forms of metaphysical dualism.
Surely this picture fits the case of animals better than the religiously tainted picture in which the immortality of the soul must be guaranteed. The mind of an octopus, say, which is remarkably rich, is not identical to its widely distributed brain, but it can hardly be deemed “immaterial” in the sense that it could exist without the octopus’s body and brain. Its mind is an adaptive organ, evolved from more primitive attributes, and not to be identified with its brain (ditto the octopus self)– yet the metaphysics of the immaterial substance hardly fits the case, or the immortality of the octopus soul (sadly). We can allow ourselves to speak of these things as distinct from the octopus’s body without incurring the charge of immaterialism. Dualism is alive and well but it is no longer in cahoots with immaterialism. There is nothing “unnatural” about accepting that the mind is an entity distinct from the brain—that is, a type of substance dualism. And there is nothing supernatural either—nothing evidencing divinity. Given that we already accept a dualism of properties, this is indeed the natural way to go: we need a suitable object to go with these properties, to be their proper subject. There was always something funny about ascribing mental properties to brains and their parts for fear of raising the specter of the immaterial soul.
 I won’t go into the full rationale for saying this here; it has been well documented elsewhere (Chomsky et al).
 The metaphysical background to what I am saying here is supplied by all those puzzles of identity we are familiar with: the statue and the piece of bronze, organisms and the matter that composes them, objects and the property bundles that characterize them, etc. Leibniz’s law does the heavy lifting in distinguishing objects we might lazily have supposed identical.
 You might try to respond by conceding the non-identity of mind and brain but contend that the former is constituted by the latter, thus preserving the spirit of materialism. The case is like the relation between a statue and the lump of matter that composes it: not identity, since they have different persistence conditions, but constitution—there is nothing more to the statue than the stuff that composes it. But this analogy fails, because it is not that the mind simply has to assume a certain shape to be what is: the mind isn’t the brain in a certain geometrical form. If there is a constitution relation here, it is nothing like the familiar paradigms. Similarly, we can’t model the mind-brain relation on, say, the relation between water and its constituent molecules: the mind is not a collection of physical constituents, viz. neurons. So the dualism is far more pronounced than these alleged models would suggest, and hence identifying the mind with the brain is a far more problematic position. In fact, we really have no idea how to understand this relation; we only know that the mind is a thing distinct from the brain, in both the identity and constitution senses. But the general nature of the link between mind and brain appears sui generis.
 There are those who proudly describe themselves as property dualists but wouldn’t be caught dead defending substance dualism. This paper is intended to allay their qualms by making some necessary distinctions. The main point is that mere ontological dualism has no immaterialist implications: all that follows is that the mind is not a congeries of neurons (with only the properties ascribed to neurons in current neuroscience).