Notoriously, however, it’s an inadequate species. The essential problem in this area is to explain how thinking manages reliably to preserve truth; and Associationism, as Kant rightly pointed out to Hume, hasn’t the resources to do so. Theproblem isn’t that association is a causal relation, or that it’s a causal relation among symbols, or even that it’s a causalrelation among mental symbols; it‘s just that their satisfaction conditions aren’t among the semantic properties thatassociates generally share. To the contrary, being Jack precludes being Jill, being salt precludes being pepper, being redprecludes being green, and so forth. By contrast, Turing’s account of thought-as-computation showed us how tospecify causal relations among mental symbols that are reliably truth-preserving. It thereby saved RTM from drowningwhen the Associationists went under.
I propose to swallow the Turing story whole and proceed. First, however, there’s an addendum I need and an aside I can‘t resist. 1 2
Addendum: if computation is just causation that preserves semantic values, then the thesis that thought is computation requires of mental representations only that they have semantic values and causal powers that preserve them. I nowadd a further constraint: many mental representations have constituent (part/whole) structure, and many mental processesare sensitive to the constituent structure of the mental representations they apply to. So, for example, the mentalrepresentation that typically gets tokened when you think . . . brown cow. . . has, among its constituent parts, the mentalrepresentation that typically gets tokened when you think . . . brown . . . ; and the computations that RTM says getperformed in processes like inferring from . . . brown cow. . . to . . . brown . . . exploit such part/whole relations. Noticethat this is an addendum (though it’s one that Turing’s account of computation was designed to satisfy). It’suntendentious that RTM tolerates the possibility of conceptual content without constituent structure since everybodywho thinks that there are mental representations at all thinks that at least some of them are primitive.3 4
The aside I can’t resist is this: following Turing, I’ve introduced the notion of computation by reference to such semantic notions as content and representation; a computation is some kind of content-respecting causal relationamong symbols. However, this order of explication is OK only if the notion of a symbol doesn’t itselfpresuppose the notion of acomputation. In particular, it‘s OK only if you don’t need the notion of a computation to explain what it is for somethingto have semantic properties. We’ll see, almost immediately, that the account of the semantics of mental representationsthat my version of RTM endorses, unlike the account of thinking that it endorses, is indeed non-computational.
Suppose, however, it’s your metaphysical view that the semantic properties of a mental representation depend, wholly or in part, upon the computational relations that it enters into; hence that the notion of a computation is prior to thenotion of a symbol. You will then need some other way of saying what it is for a causal relation among mentalrepresentations to be a computation; some way that does not presuppose such notions as symbol and content? It may be possible tofind such a notion of computation, but I don’t know where. (Certainly not in Turing,who simply takes it for granted that the expressions that computing machines crunch are symbols; e.g. that they denotenumbers, functions, and the like.) The attempts I’ve seen invariably end up suggesting (or proclaiming) that every causalprocess is a kind of computation, thereby trivializing Turing’s nice idea that thought is.
So much for mental processes.
Fourth Thesis: Meaning is information(more or less).
There actually are, in the land I come from, philosophers who would agree with the gist of RTM as I’ve set it forth so far. Thesis Four, however, is viewed as divisive even in that company. I’m going to assume that what bestows contenton mental representations is something about their causal-cum-nomological relations to the things that fall underthem: for example, what bestows upon a mental representation the content dog is something about its tokenings beingcaused by dogs.