Wolfgang Schwarz

What the Ability Hypothesis Is Not

According to the Lewis-Nemirow ability hypothesis, knowing what it's like to see red is having a certain cluster of abilities. According to almost everybody who writes about the ability hypothesis, the hypothesis also claims that knowing what it's like neither is nor involves any kind of knowledge-that. This is indeed suggested by some of Lewis' remarks, in particular by this one on p.288 of "What Experience Teaches" (in Papers):

The Ability Hypothesis says that knowing what an experience is like just is the possession of [...] abilities to remember, imagine, and recognize. It isn't the possession of any kind of information, ordinary or peculiar.

One has to read the rest of the paper to find out that by "information", Lewis here most probably means exclusion of possible worlds. At any rate, it is clear from the rest of the paper that Lewis doesn't claim that all Mary learns are abilities.

For instance, he agrees (pp.268f. and 287) that certainly Mary acquires new indexical or de se knowledge, like the knowledge that she is seeing colours now. She couldn't know this before she was released simply because it wasn't true at the time. The same can be said about de se knowledge involving demonstrative reference to experiences: Only when she sees colours can she know that this (kind of) experience is a red experience. And only now can she wonder whether other people also have this (kind of) experience when they see ripe tomatoes. Lewis doesn't deny any of this. He merely argues (p.269) that such de se knowledge isn't strictly necessary for knowing what it's like, hence it shouldn't be identified with knowledge what it's like.

Nor does Lewis deny that Mary acquires new mental representations, i.e. new words or concepts in her language of thought, and that she can formulate new thoughts employing these new concepts (pp.278f. and 290). He doesn't fully endorse this view because he thinks it's an open question whether there is a language of thought. But he finds it at least plausible. So Lewis doesn't deny that in a sense Mary learns old facts in a new guise. Even less does he deny that Mary learns new structured (hyperintensional) propositions, or new modes of presentation of Russellian propositions. Again, he merely argues (p.279) that this alone can't explain Mary's epistemological progress. For, he says, one presumably also acquires new mental representations by learning Russian, but we wouldn't say that there are special facts that can only be known by people who know Russian. As Lewis concedes, this complaint presupposes that the new phenomenal concepts are in principle translatable into non-phenomenal concepts, just as Russian words are translatable into non-Russian words. Type-B materialists putting forward the old facts/new guise explanation would of course deny that. They would argue that even though Mary's newly possessed hyperintensional 'information' is necessarily equivalent with some physical information, it is not conceptually reducible to the latter. That is, the epistemic possibilities Mary can exlcude are not metaphysical possibilities; they are a posteriori impossibilities. Lewis, like Jackson and Chalmers (and me), thinks that this won't work.

But whether or not he is right here is somewhat besides the point. What's important is that Lewis doesn't claim that all Mary learns are abilities. He explicitly accepts that she may also acquire new de se knowledge and new concepts and thereby new hyperintensional 'information' (though Lewis would rather not call it 'information'). That's why he says in "Reduction of Mind" (293f. in Papers, my italics):

Materialists have said many things about what does happen in [the Mary case]. I myself, following Nemirow, call it a case of know-how: Mary gains new imaginative abilities. Others have said that Mary gains new relations of acquaintance, or new means of mental representation; or that the change in her is just that she has now seen colour. These suggestions need not be taken as rival alternatives.

He goes on to say that it is quite irrelevant "whether these various happenings could in any sense be called the gaining of 'new knowledge', 'new belief', or 'new information'", as long as they are not new information in the sense of exclusion of possible worlds. It has been suggested to me that in this paragraph Lewis has abandoned the ability hypothesis as being the correct answer to the knowledge argument. But this contradicts the fact that he clearly endorses the ability hypothesis in the second sentence of the paragraph. In fact, the whole paragraph could just as well occur in "What Experience Teaches". For as I've tried to convince you above, here too Lewis accepts that Mary gains new relations of acquaintance, new means of mental representation, and new indexical knowledge. And here too he says it's unimportant whether some of the things Mary learns are called "information" as long as it's not exlusion of worlds.

Why does this matter? Because most objections to the ability hypothesis simply ignore it. It is commonly assumed that if one can show that Mary acquires any kind of 'information' or knowledge-that, like the knowledge that this is what it's like to see red, then the ability hypothesis is refuted. It seems that those who put forward these objections have only read page 288 of "What Experience Teaches". From the rest of the paper I think it's clear that these objections doesn't even threaten Lewis' position. To argue against Lewis, one must show either 1) that the abilities Lewis cites are not necessary or sufficient for knowing what it's like, or 2) that gaining these abilities necessarily involves gaining information in the sense of excluding metaphysically possible worlds. (See Earl Conee, Torin Alter and Michael Tye for arguments in support of (1).) Everything else is just missing the point.