[ Pobierz całość w formacie PDF ]
reason that a capacity for John loves Mary
end p.97
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 Mary thoughts is that they
don't have the same constituents. Who could really doubt that this is so? Systematicity
seems to be one of the (very few) organizational properties of minds that our cognitive
science actually makes some sense of.
If your favourite cognitive architecture doesn't support a productive cognitive repertoire,
you can always argue that since minds are really finite, they aren't literally productive.
But systematicity is a property that even quite finite conceptual repertoires can have; it
isn't remotely plausibly a methodological artefact. If systematicity needs compositionality
to explain it, that strongly suggests that the compositionality of mental representations is
mandatory. For all that, there has been an acrimonious argument about systematicity in
the literature for the last ten years or so. One does wonder, sometimes, whether cognitive
science is worth the bother.
Some currently popular architectures don't support systematic representation. The
representations they compute with lack constituent structure; a fortiori they lack
compositional constituent structure. This is true, in particular, of neural networks .
Connectionists have responded to this in a variety of ways. Some have denied that
concepts are systematic. Some have denied that Connectionist representations are
inherently unstructured. A fair number have simply failed to understand the problem. The
most recent proposal I've heard for a Connectionist treatment of systematicity is owing to
the philosopher Andy Clark (1993). Clark says that we should bracket the problem of
systematicity. Bracket is a technical term in philosophy which means try not to think
about.
I don't propose to review this literature here. Suffice it that if you assume
compositionality, you can account for both systematicity and productivity; and if you
don't, you can't. Whether or not productivity and systematicity prove that conceptual
content is compositional, they are clearly substantial straws in the wind. I find it
persuasive that there are
end p.98
quite a few such straws, and they appear all to be blowing in the same direction.
The Best Argument for Compositionality
The best argument for the compositionality of mental (and linguistic) representation is
that its traces are ubiquitous; not just in very general features of cognitive capacity like
productivity and systematicity, but also everywhere in its details. Deny productivity and
systematicity if you will; you still have these particularities to explain away.
Consider, for example: the availability of (definite) descriptions is surely a universal
property of natural languages. Descriptions are nice to have because they make it possible
to talk (mutatis mutandis, to think) about a thing even if it isn't available for ostension
and even if you don't know its name; even, indeed, if it doesn't have a name (as with ever
so many real numbers). Descriptions can do this job because they pick out unnamed
individuals by reference to their properties. So, for example, the brown cow picks out a
certain cow; viz. the brown one. It does so by referring to a property, viz. being brown,
which that cow has and no other cow does that is contextually relevant. Things go wrong
if (e.g.) there are no contextually relevant cows; or if none of the contextually relevant
cows is brown; or if more than one of the contextually relevant cows is brown . . . And so
forth.
OK, but just how does all this work? Just what is it about the syntax and semantics of
descriptions that allows them to pick out unnamed individuals by reference to their
properties? Answer:
i.Descriptions are complex symbols which have terms that express properties among
their syntactic constituents;
and
ii.These terms contribute the properties that they express to determine what the
descriptions that contain them specify.
It's because brown means brown that it's the brown cow that the brown cow picks out.
Since you can rely on this arrangement, you can be confident that the brown cow will
specify the local brown cow even if you don't know which cow the local brown cow is;
even if you don't know that it's Bossie, for example, or that it's this cow. That, however,
is just to say that descriptions succeed in their job because they are compositional. If
English didn't let you use brown context-independently to mean brown, and cow
context-independently to mean cow, it couldn't let you use the brown cow to specify a
brown cow without naming it.
end p.99
Names, by contrast, succeed in their job because they aren't compositional; not even
when they are syntactically complex. Consider the Iron Duke , to which Iron does not
contribute iron, and which you can therefore use to specify the Iron Duke even if you
don't know what he was made of. Names are nicer than descriptions because you don't
have to know much to specify their bearers, although you do have to know what their
bearers are called. Descriptions are nicer than names because, although you do have to
know a lot to specify their bearers, you don't have to know what their bearers are called.
What's nicer than having the use of either names or descriptions is having the use of both.
I agree that, as a piece of semantic theory, this is all entirely banal; but that's my point, so
don't complain. There is, to repeat, no need for fancy arguments that the representational
systems we talk and think in are in large part compositional; you find the effects of their
compositionality just about wherever you look.
I must apologize for having gone on at such length about the arguments pro and con
conceptual compositionality; the reason I've done so is that, in my view, the status of the
statistical theory of concepts turns, practically entirely, on this issue. And statistical
theories are now the preferred accounts of concepts practically throughout cognitive
[ Pobierz całość w formacie PDF ]