Apropos the Knowledge Argument
The knowledge argument tells us that complete physical knowledge of the world is not complete knowledge of the world—in particular, it is not complete knowledge of the mind. How interesting is this conclusion? It depends what we mean by “physical”. Suppose we mean “included in Newtonian physics”, with its talk of mass, gravity, space, and motion. That would not be terribly interesting, because the science of physics has long since expanded its inventory of the physical (electromagnetism, fields of force, unobservable particles, etc.). It would be like saying that knowledge of Cartesian physics, in which only extension is recognized as physical, is insufficient for knowledge of the mind. That would be a very implausible materialist doctrine that no one today would be attracted by. And matters are not much helped by saying “physical” means “what is contained in current physics”, since it too will probably expand its conceptual resources with time. On the other hand, if we mean physics as conceived by Russell and Eddington, we get a quite different answer, because they included a mental component in their account of the physical world (“neutral monism”). If matter has a mental nature, then knowledge of it might well add up to knowledge of mind, depending on how much of the mind we choose to inject into the physical world. Then again, we might choose to mean by “physical” something like “pertaining to the body”, as opposed to the supernatural soul or spirit. If we meant that, knowledge of the physical would certainly entail knowledge of the mind, since everything about the mind arises from the brain–there being no immortal soul or spirit. Having a sensation of red is bodily in this sense, since it is caused by the brain; so, it’s a “physical” thing (not a “spiritual” thing). It has a bodily correlate and cause, not an immaterial basis in the soul (compare different conceptions of the nature of mental illness). None of these possible answers is particularly interesting, and the answers differ according to the conception of the “physical” being adopted. And what other conceptions are there? The knowledge argument is therefore bedeviled by the old problem of defining the “physical” (see Hempel, Chomsky, et al). What is an interesting question is the following: Is there a description of the mind and a description of the brain under which there is an a prioriconnection between the two? Here we don’t use the word “physical” (or indeed the word “mental”); we leave it open what kind of description might have the property in question, viz. allowing for an a priori connection. In other words, are there any concepts applicable to the brain that might lead to a priori entailments to concepts applicable to the mind as ordinarily conceived? We don’t call these concepts physical or non-physical (concepts we might well reject as ill-defined) and simply ask whether any concepts could provide the necessary entailments. For if there were such concepts, knowledge of the one would provide knowledge of the other as an a priori matter. Now that is an interesting question. But it is not a question that is easy to answer, mainly because we have very little idea what these concepts might be. Nagel once suggested that such bridging concepts might be provided by what he called “objective phenomenology”, the idea being that such concepts would have some chance of straddling the conceptual divide by being both objective and phenomenological. This suggestion is certainly worth pursuing, but we can also expand the idea to include any concepts that might deliver the requisite entailments—including those not accessible to human thinkers.What might we call such a doctrine? We might try “quasi-physicalism”, but that still contains the word “physical” and “quasi” doesn’t give us much guidance as to how far we can depart from customary uses of “physical” (there are several). No convenient label suggests itself, so I propose just calling it “brain-ism” or “somatic-ism”: that is, the claim that mental attributes are a priori entailed by descriptions of the brain or body—but descriptions not aptly classified as “physical” or “material”. We need to add that these descriptions must not be our ordinary mental descriptions, on pain of triviality; nor need they be expressible in any human language. They are stipulated to be different from our ordinary mental and cerebral descriptions, though intimately related to them. It seems to me very likely that such descriptions exist—or else the mind-body problem has no solution. Something must intelligibly link the two—some kind of a priori necessitation. The knowledge argument would be powerless against such a view, because knowledge of the one would provide knowledge of the other: B-concepts would entail M-concepts (where B-concepts apply to the brain and M-concepts apply to the mind—without being our usual concepts of brain and mind). If there were a proof that no such concepts could exist, then we would have a form of the knowledge argument that refuted any theory along these lines, leaving us only with a bare and irreducible dualism. But I know of no such argument and it seems to me that there must be descriptions of the requisite type, on pain of rendering the world absurd (with a miracle-performing pineal gland at its heart). The “world-knot” must be capable of being untangled, whether this is achievable by us or not. The usual formulations of the knowledge argument are rather like arguing that geometrical knowledge never entails phenomenological knowledge (of course not!), but the knowledge argument directed at other types of brain and mind description is unlikely to be persuasive. The argument is either too easy or too ambitious.
 Does anyone believe that the phenomena currently recognized by physics can all be explained by the concepts currently employed by physics? Black holes, dark matter, dark energy, quantum entanglement, pre-big-bang cosmology—can these be explained without introducing new concepts into physics? Unlikely.
 See “What is it Like to be a Bat?” (1972).
 A possibility is that some kind of quantitative description of brain and mind might provide the necessary a priori link, but this is nothing more than a glint in the metaphysician’s eye. Still, the idea of a mathematical unification has its attractions: an identity of mathematical structure (“homeomorphism”) would go a long way towards bridging the gulf.
 Suppose we had only color knowledge of water; that would never add up to knowledge of the boiling potential of water. This would show that “colorism” about water is a mistaken doctrine. But of course, water has other properties that do suffice to provide a priori links to its ability to boil (the motion of separable sliding particles), so a molecular theory of water is not refuted by any knowledge argument. A person without the concept of a molecule would be in the dark about water’s ability to boil, but not someone with that concept.