RTM says that there is no believing-that-P episode without a corresponding tokening-of-a-mental-representation episode, and it contemplates no locus of original intentionality except the contents of mental representations. Inconsequence, so far as RTMs are concerned, toexplain what it is for a mental representation to mean what it does is to explain what it is for a propositional attitude tohave the content that it does. I suppose that RTM leaves open the metaphysical possibility that there could be mentalstates whose content does not, in this sense, derive from the meaning of corresponding mental representations. But ittakes such cases not to be nomologically possible, and it provides no hint of an alternative source of propositional objectsfor the attitudes.
Finally, English inherits its semantics from the contents of the beliefs, desires, intentions, and so forth that it’s used to express, as per Grice and his followers. Or, if you prefer (as I think, on balance, I do), English has no semantics. LearningEnglish isn’t learning a theory about what its sentences mean, it’s learning how to associate its sentences with thecorresponding thoughts. To know English is to know, for example, that the form of words ‘there are cats’ is standardlyused to express the thought that there are cats; and that the form of words ‘it’s raining’ is standardly used to expressthe thought that it’s raining; and that the form of words ‘it’s not raining’ is standardly used to express the thought thatit’s not raining; and so on for in(de)finitely many other such cases.
Since, according to RTM, the content of linguistic expressions depends on the content of propositional attitudes, and the content of propositional attitudes depends on the content of mental representations, and since the intended senseof ‘depends on’ is asymmetric, RTM tolerates the metaphysical possibility of thought without language; for that matter,it tolerates the metaphysical possibility of mental representation without thought. I expect that many of you won’t likethat. I’m aware that there is rumoured to be an argument, vaguely Viennese in provenance, that proves that ‘original’,underived intentionality must inhere, not in mental representations nor in thoughts, but precisely in the formulas ofpublic languages. I would be very pleased if such an argument actually turned up, since then pretty nearly everything Ibelieve about language and mind would have been refuted, and I could stop worrying about RTM, and about whatconcepts are, and take off and go sailing, a pastime that I vastly prefer. Unfortunately, however, either nobody canremember how the argument goes, or it’s a secret that they’re unprepared to share with me. So I’ll forge on.
Third Thesis: Thinking is computation.
A theory of mind needs a story about mental processes, not just a story about mental states. Here, as elsewhere, RTM is closer in spirit to Hume than it is to Wittgenstein or Ryle. Hume taught that mental states are relations to mentalrepresentations, and so too does RTM (the main difference being, as we’ve seen, that RTM admits, indeed demands,mental
representations that aren’t images). Hume also taught that mentalprocesses (including, paradigmatically, thinking) are causal relations among mental representations..5 So too does RTM. In contrast to Hume, and to RTM, the logical behaviourism ofWittgenstein and Ryle had, as far as I can tell, no theory of thinking at all (except, maybe, the silly theory that thinkingis talking to oneself). I do find that shocking. How could they have expected to get it right about belief and the likewithout getting it right about belief fixation and the like?
Alan Turing’s idea that thinking is a kind of computation is now, I suppose, part of everybody’s intellectual equipment; not that everybody likes it, of course, but at least everybody’s heard of it. That being so, I shall pretty much take it asread for the purposes at hand. In a nutshell: token mental representations are symbols. Tokens of symbols are physicalobjects with semantic properties. To a first approximation, computations are those causal relations among symbolswhich reliably respect semantic properties of the relata. Association, for example, is a bona fide computational relationwithin the meaning of the act. Though whether Ideas get associated is supposed to depend on their frequency,contiguity, etc., and not on what they’re Ideas of, association is none the less supposed reliably to preserve semanticdomains: Jack-thoughts cause /ill-thoughts, salt-thoughts cause pepper-thoughts, red-thoughts cause green-thoughts, andso forth.6 So, Hume’s theory of mental processes is itself a species of RTM, an upshot that pleases me.