The traditional locus of the inference from finite determination to finite representation is, however, not Mentalese but English (see Chomsky 1965; Davidson 1967). Natural languages are learned, and learning is an ‘act of intellection’ parexcellence. Doesn’t that show that English has to have a compositional semantics? I doubt that it does. For one thing,as a number of us have emphasized (see Chapter 1; Fodor 1975; Schiffer 1987; for a critical discussion, see Lepore1997), if you assume that thinking is computing, it’s natural to think that acquiring a natural language is learning how totranslate between it and the language you compute in. Suppose that language learning requires that the translationprocedure be ‘grasped’ and grasping the translation procedure requires that it be finitely
and explicitly represented. Still, there is no obvious reason why translation between English and Mentalese requires having a compositional theory of content for either language. Maybe translation to and from Mentalese is a syntacticalprocess: maybe the Mentalese translation of an English sentence is fully determined given its canonical structuraldescriptions (including, of course, lexical inventory).
I don’t really doubt that English and Mentalese are both productive; or that the reason that they are productive is that their semantics is compositional. But that’s faith in search of justification. The polemical situation is, on the one hand,that minds are productive only under a tendentious idealization; and, on the other hand, that productivity doesn’tliterally entail semantic compositionality for either English or Mentalese. Somebody sane could doubt that theargument from productivity to compositionality is conclusive.
The Systematicity Argument for Compositionality
‘Systematicity’ is a cover term for a cluster of properties that quite a variety of cognitive capacities exhibit, apparently as a matter of nomological necessity.54 Here are some typical examples. If a mind can grasp the thought that P ^ Q, it cangrasp the thought that Q ^ P; if a mind can grasp the thought that CP( Q), it can grasp the thought that B and thethought that QP; if a mind can grasp the thought that Mary loves John, it can grasp the thought that John loves Mary. . .etc. Whereas it’s by no means obvious that a mind that can grasp the thought that P ^ Q can also grasp the thoughtthat R ^ Q (not even if, for example, (P ^ Q) ^ (R ^ Q). That will depend on whether it is the kind of mind that’sable to grasp the thought that R. Correspondingly, a mind that can think Mary loves John and John loves Mary may nonethe less be unable to think Peter loves Mary. That will depend on whether it is able to think about Peter.
It seems pretty clear why the facts about systematicity fall out the way they do: mental representations are compositional, and compositionality explains systematicity.55 The reason that a capacity for John loves Mary
It’s been claimed that (at least some) facts about the systematicity of minds are conceptually necessary; ‘we wouldn’t call it thought if it weren’t systematic’ (see e.g. Clark 1991). I don’t, in fact, know of any reason to believe this, nor do I care much whether it is so. If it’s conceptually necessary that thoughts are systematic, then it’s nomologicallynecessary that creatures like us have thoughts, and this latter necessity still wants explaining.
It’s sometimes replied that compositionality doesn’t explain systematicity since compositionality doesn’t entail systematicity (e.g. Smolensky 1995). But that only shows that explanation doesn’t entail entailment. Everybody sensible thinks that the theory of continental drift explains why (e.g.) South America fits so nicely into Africa. It does so,however, not by entailing that South America fits into Africa, but by providing a theoretical background in which the fact that they fit comes, as it were, as no surprise.Similarly, mutatis mutandis, for the explanation of systematicity by compositionality.Inferences from systematicity to compositionality are ‘arguments to the best explanation’,and are (of course) non-demonstrative; which is (of course) not at all the same as their being implausible or indecisive. Compare Cummins 1996, which appears to be confusedabout this.
thoughts implies a capacity for Mary loves John thoughts is that the two kinds of thoughts have the same constituents; correspondingly, the reason that a capacity for John loves Mary thoughts does not imply a capacity for Peter loves Marythoughts is that they don’t have the same constituents.Jean-marc pizano