Jackson’s argument goes roughly like this. Imagine that Mary, a master neuroscientist of the future, has lived her entire life in a black and white room, never having had any experience of colors. But she knows everything there is to know about the physical facts concerning the physics and physiology of color perception. Thus, though she’s never seen a red object herself, she knows exactly what happens in other people’s eyes and nervous systems when they see red, as well as all the relevant facts about light, surface reflectance properties of red objects, and so on. Eventually she leaves the room and sees a red object for the first time. Does she learn something new? Jackson says she clearly does – she learns what it’s like to see red. And that (so the argument goes) suffices to refute physicalism. For physicalism claims that to know all the physical facts about human beings is to know all the facts about them, period. But though Mary knew all the relevant physical facts about color perception prior to her release from the room, she didn’t know all the facts, because she learned something new upon her release. Hence there is more to human nature than is captured by a description of the physical facts. In particular, facts about qualia (such as the facts about what it’s like to see red) are additional facts, beyond the physical facts.
I will have more to say about the knowledge argument – and in particular about Jackson’s later change of heart about it – in a future post. For now let’s consider Churchland’s objection, which he first stated in his paper “Reduction, Qualia, and the Direct Introspection of Brain States” and repeated in his later paper “Knowing Qualia: A Reply to Jackson.” (Both papers are reprinted in Churchland’s book A Neurocomputational Perspective, which is the source of the quotes below.) In the course of making several other criticisms of Jackson, Churchland says that if the knowledge argument were sound, it would refute substance dualism for the same reasons it would refute materialism. For we need only run the argument by imagining instead that Mary is a master “ectoplasmologist” with knowledge of the “hidden constitution and nomic intricacies” of ectoplasm, and in particular of “everything there is to know about the ectoplasmic processes underlying vision” (“Reduction, Qualia, and the Direct Introspection of Brain States,” p. 63). Since Mary would learn something new upon leaving the room despite knowing everything there is to know about ectoplasm, this parallel argument “would ‘show’ that there are some aspects of consciousness that must forever escape the ectoplasmic story” (“Knowing Qualia,” p. 72, emphasis in the original).
But Churchland is just making the same mistake we saw Stoljar make. What philosophical dualist ever said anything about “ectoplasmic processes,” or about the “hidden constitution” or “nomic intricacies” of an immaterial substance? Even apart from the “ectoplasm” nonsense – which is, of course, just a rhetorical flourish intended to make dualism sound ridiculous before it is even given a hearing – Churchland’s description of dualism is a ludicrous caricature. He makes it sound as if the dualist were committed to the existence of an object which is just like a material object in having various parts arranged in a certain way so as to behave according to law-like regularities, only one made out of some ghostly kind of stuff rather than of matter. But that is precisely the opposite of what a Plato, an Aquinas, or a Descartes actually held. For them, as for philosophical dualists generally, the soul is necessarily something simple or non-composite, and thus without parts of either a material or a quasi-material sort. Hence it has no “hidden constitution” or “nomic intricacies” of the sort Churchland has in mind. It is not a kind of ghostly mechanism because it is not a “mechanism” at all. (True, Descartes was a mechanist, but only concerning the material world, not the mind.)
For the Cartesian dualist, who is Churchland’s immediate target, the essence of the soul is just to think, and thought is (on this view) essentially conscious. As Descartes says in a letter to Mersenne, “nothing can be in me, that is to say, in my mind, of which I am not conscious” (Descartes, Philosophical Letters, p. 90, emphasis in original), and as he writes in the replies to the Second Set of Objections, “thought is a word that covers everything that exists in us in such a way that we are immediately conscious of it” (Haldane and Ross, Philosophical Works of Descartes, vol. II, p. 52, emphasis in original). In the Fifth Set of Objections, Gassendi had complained that Descartes fails to provide an account of the “internal substance” of the mind, which would require something analogous to the “chemical investigation” by which we discover what unseen properties of wine determine its surface features (Cottingham, Stoothoff, and Murdoch, Philosophical Writings of Descartes, vol. II, p. 193). Descartes replied, in words that could have been directed at Churchland: “You want us, you say, to conduct ‘a kind of chemical investigation’ of the mind, as we would of wine. This is indeed worthy of you, O Flesh, and of all those who have only a very confused conception of everything, and so do not know the proper questions to ask about each thing” and (in response to another of Gassendi’s objections) that “your purpose was simply to show us what absurd and unjust quibbles can be thought up by those who are more anxious to attack a position than to understand it” (Ibid., pp. 248-49). For Descartes, your res cogitans isn’t something which, by virtue of some hidden internal constitution, generates your consciousness; your res cogitans just is your consciousness.
For that reason, there can be no “knowledge argument” against substance dualism parallel to Jackson’s argument against physicalism. If the Mary of Churchland’s alternate scenario does not know what it is like to experience red before leaving the room, then she just does not and cannot know everything there is to know about res cogitans, because experiencing red is nothing more than a mode of consciousness and (therefore) a mode of res cogitans. To know everything there is to know about a res cogitans would not involve knowing about its internal constitution, the causal relations holding between its parts, etc. (for it has none of these things) but would involve instead knowing every kind of conscious thought or experience it might have – including experiencing red. The “gap” between two kinds of fact that Jackson’s original argument points to does not have even a prima facie parallel in the substance dualist case. The physicalist has to acknowledge at least a conceptual difference between physical facts and facts about consciousness; the only question is whether there is also a metaphysical difference. But there is, according to the Cartesian dualist, not even a conceptual difference between facts about res cogitans and facts about consciousness. That’s Descartes’ whole point.
Whatever other objections the physicalist might raise against dualism, then, the tu quoque strategy employed by Churchland and many other contemporary materialists is simply incompetent. It rests on a fundamental misunderstanding of what the dualist means by an “immaterial substance.” Equally incompetent is any critique of dualism that treats it (as Churchland evidently does in “Knowing Qualia”) as a kind of quasi-scientific empirical theory – that is, as if it were “postulating” the existence of immaterial substance as the “best explanation” of mental phenomena among the various alternatives. As I noted in a previous post on Churchland, that is not at all what the most significant dualists in the history of philosophy were up to. Their arguments for dualism are intended instead as strict metaphysical demonstrations of the existence of the soul. One may or may not think the attempted demonstrations succeed, but one will not refute them unless one first understands what sort of argument they are intended to be. Dualists traditionally tend to regard metaphysical inquiry as an enterprise every bit as rational as, but distinct from and more fundamental than, empirical science. Committed as they often are to scientism, contemporary materialists would no doubt deny that there can be any such form of inquiry, but they cannot deploy this denial in an argument against dualism without begging the question.
Their unreflective scientism is no doubt one source of contemporary materialists’ systematic misunderstanding of dualism. Since they think all rational inquiry must be a kind of scientific inquiry, they tend to (mis)interpret the claims of dualists (as they often do the claims of theists) as if they were feeble exercises in empirical hypothesis formation. It seems to me that another source might be the enormous influence Gilbert Ryle’s book The Concept of Mind had on mid-twentieth century philosophy. For Ryle there characterized Descartes’ position, absurdly, as a “para-mechanical hypothesis” on which minds are “rather like machines but also considerably different from them,” being “spectral machines” that are “complex organized unit[s]” which run on “counterpart” principles to those of physical substances, “made of a different sort of stuff and with a different sort of structure” which might be thought of “not [as] bits of clockwork [but rather] just bits of not-clockwork” and where the “bits” are arranged into a “field of causes and effects” (pp. 18-20). It is as if Churchland’s generation of materialists got their “knowledge” of what dualists believe from reading Ryle, and the generations since have gotten their “knowledge” from reading people like Churchland.
In any event, the materialist who characterizes the soul in terms of “ectoplasm” is like the atheist who compares the God of classical theism to the “Flying Spaghetti Monster” or thinks that the cosmological argument starts with the premise that “Everything has a cause…” Not to put too fine a point on it, neither one knows what the hell he is talking about or has any business opening his mouth on the subjects in question.