What is Physicalism? Jackson (1986): Physicalism is not the noncontroversial thesis that the actual world is largely physical, but the challenging thesis that it is entirely physical. This is why physicalists must hold that complete physical knowledge is complete knowledge simpliciter. Jackson (1994): Any world that is a minimal physical duplicate of our world is a duplicate simpliciter of our world. MPD = A world built with all & only the physical material of the actual world, put together in exactly the same way. 1 Meet Mary the Omniscient Scientist Frank Jackson (1986): Mary is confined to a B/W room, is educated through B/W books and through lectures relayed on B/W television. In this way she learns everything there is to know about the physical nature of the world. She knows all the physical facts about us and our environment, in a wide sense of physical which includes everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon this, including of course functional roles. If physicalism is true, she knows all there is to know. Knowledge Argument (1986): (1) Mary (before her release) knows everything physical there is to know [about other people]. (2) Mary (before her release) does not know everything there is to know [about other people] (because she learns something about them on her release). (3) Therefore, there are truths about other people (and herself) which escape the physical story. 2 1
The Knowledge Argument (KA) (1) Mary (before her release) knows everything physical there is to know about other people. (2) Mary (before her release) does not know everything there is to know about other people (because she learns something about them on her release). (3) There are truths about other people (and herself) which escape the physicalist story. Churchland s 1 st Formulation: (1) ( x)[(hx & Px) Kmx] (2) ( x)[hx & ~Kmx] (viz., "what it is like to see red") (3) ( x)[hx & ~Px] Translation: (1) For all knowables x, if x is about humans and physical, then Mary knows x. (2) There is something x that is about humans but Mary does not know it. (3) Therefore, there is something x about humans that is not physical. 3 (1) ( x)[(hx & Px) Kmx] (2) ( x)[hx & ~Kmx] (3) ( x)[hx & ~Px] Churchland s Criticism of KA Formally valid argument (i.e., if you accept the premises as true, you have to accept the conclusion as true) But are the premises actually true? According to Churchland, it depends on how you interpret the predicate K ( knows about ): If it is propositional knowledge expressible in terms of knowledge-that, (1) is true but (2) isn t If it is not propositional knowledge, but rather like knowledge-how, (1) is false but (2) is true So there is no univocal interpretation of K under which both premises are true. So keeping premises as acceptable to a materialist requires that K be interpreted as having different meanings in both premises, which makes the argument invalid (to see this, just replace K with different predicate letters in (1) & (2) ). Or else, the argument is unsound by virtue of having a false premise. 4 2
Know-that vs. Know-how Is it plausible that Mary, upon her release, gains merely a knowledge-how, a skill? It seems that Mary acquires new concepts denoting her color sensations, e.g., what it s like to see red. This is evidence by the fact that she can make judgments about them in a way she was not able to before. E.g., what it is like to see orange is more like what it is like to see red than what it s like to see blue, or If what it is like to see red is like that, then I ll try to have more experiences like that (where that refers to the reddish quality of her visual experience while looking at a crimson vase). But if she acquires new concepts and is now capable of making new judgments deploying them that she was incapable of before, then what she learns is knowledge-that, not just knowledge-how. So Churchland's criticism of KA fails. How might Churchland respond to this? 5 The Knowledge Argument against Substance Dualism (1) Let 'E' stand for 'is about something ectoplasmic in character' (where 'ectoplasm' is an arbitrary name for the dualist's nonphysical substance), and (2) Alter the story so that Mary becomes an exhaustive expert on a completed ectoplasmic science of human nature. (1) ( x)[(hx & Ex) Kmx] (2) ( x)[hx & ~Kmx] (3) ( x)[hx & ~Ex] The dualist, according to Churchland, must protest for the same reason that a materialist would protest: the premises are acceptable only if the knowledge in question is interpreted as different in the two premises. 6 3
Churchland 2 nd Formulation of KA The first premise must assert that, for any knowable x, and for any form f of knowledge, if x is about humans and x is physical in character, then Mary knows(f) about x. The second premise is modified in the same modest fashion, and the conclusion is identical. (1') ( x)( f)[(hx & Px) K(f)mx] (2') ( x)( f)[hx & ~K(f)mx] (3') ( x)[hx & ~Px] But now the argument is unsound even though it is formally valid: (1) is clearly false according to Churchland and not acceptable to a materialist. 7 Converting a Third-Person Account into a First-Person Account According to Churchland, when we learn new scientific concepts, it is all a matter of habituation to get used to applying them instead of old concepts of the folk. That is what happened when stop thinking of Heavens in terms of crystal spheres with holes in them and start using the terms of new modern astronomy. Same will happen when we have a mature neuroscience. We will apply its terms instead of using the old and defective terms of folk psychology like belief, desire, pain, etc. How plausible is this? Most folk psychological terms are intentional (having representational content), and that is where their usefulness lies. How is talking in brain state terms going to help? 8 4
Jackson s (1994) Defense 1 1) Let P stand for the complete microphysical description of the world, and K for the complete description of all truths/facts entailed by P. 2) P&K describes all facts about our world according to the physicalist, and that is what Mary knows. 3) Further: (P K), that is, the entailment is metaphysical necessitation. 4) So for any particular truth, K i, (P K i ). 5) However, for Jackson, this can t be a brute fact, and needs explanation. 6) The only plausible explanation is that given our ordinary competence with the semantics of terms/concepts involved in the expression/ judgment of K i, and sufficient acumen, we can a priori figure out how K i follows from P, that is P K i is a conceptual truth. 7) For example, we are able to figure out a priori how water facts are made true (explained) by H2O facts. In the absence of a conceptual connection, all we would have are metaphysically brute necessary correlations. There would be no or very little intelligible connection between the two sets of truths. 9 Jackson s (1994) Defense 2 8) If physicalism is not to be a mysterious doctrine, not only all Ks must follow this pattern, but as a matter of fact, they do follow this pattern, except when the the truths in question are phenomenological truths (call these, C) like people sometimes feel pain 9) While in the B/W room, Mary, who knows P, can derive all Ks except the truths about color phenomenology that she comes to know only after her release. 10) But even after acquiring this body of phenomenological knowledge after her release, it remains conceptually isolated: Mary still cannot derive it a priori, cannot explain it by appeal to P; that is, the connection still is unintelligible, except that now she at least possesses this knowledge and enjoys it very much, delights in it, etc. 11) So there are some truths, C, not entailed by P; thus physicalism is false. 12) The reason why phenomenological truths cannot be derived from P is because phenomenal concepts have no a priori conceptual analyses; or put less strongly, they have no cognitive reference fixers. 10 5