A commentary on Paul Bloom's How Children Learn the Meanings of Words, MIT Press, 2000
To appear in Behavioral and Brain Sciences
The empiricist supposes that word learning involves only general inferential abilities. While Bloom acknowledges the relevance of such abilities (p. 211), and does not believe there is a mechanism whose special purpose is to facilitate word learning per se, he proposes a key role for mechanisms whose special purposes are more broadly defined - e.g. a theory of mind, an understanding of principles of individuation, and an essentialist ability to form concepts. We think that the considerations Bloom marshals in favour of his theory in fact support the central involvement of a general purpose mechanism.
Consider the nature of the knowledge acquired through word learning. Despite his objections to associationism, Bloom describes learning the meaning of a word as acquiring an "association" (p. 17) or a "mapping" (p. 89) between a form and a concept or mental representation. Actually, given his position that word learning is a product of inference, it seems that what he should say is that learning the meaning of a word is learning some kind of fact. In the case of referring terms, one learns something about a word, e.g. "cat": that it refers to instances of the kind cat. (At the same time, one learns about the kind cat that its instances are called "cat.") This knowledge does not differ in format from any other knowledge one might acquire about the environment.
Bloom's commitment to an essentialist theory of many concepts coheres well with the following picture of how a general purpose mechanism could explain word learning. Essentialism is adaptive (p. 153) because regularities in the world are organized around "sources of correlation" (Ryder, submitted) or "substances" (Millikan, 1998; 2000). These are entities in the environment, e.g. real kinds and individuals, that have a set of correlated features where this correlation occurs for a reason. Essentialism encourages the conceptual tracking of sources of correlation. Concepts allow one to re-identify kinds or individuals as the same again, so that you can infer the presence of their currently unobservable features, and learn more about them in order to facilitate re-identification in the future (Millikan, 1998; 2000). This is what explains successful learning and induction (Bloom, p. 153). Obviously, it is to an organism's advantage to learn as many facts about a source of correlation as possible, to permit more induction and easier re-identification.
Now let us apply this idea to word learning. In order to believe that "cat" refers to cats, one needs three concepts: a concept of the word "cat", a concept of reference, and a concept of cats. Bloom is a psychological essentialist about the third concept; suppose that this is the correct stance to adopt towards the other two as well - after all, the word "cat" and intentions to refer are both kinds that have a set of features that are correlated for an underlying reason (social convention in one case, and human psychology in the other). According to the hypothesis bruited above, our cognitive system is set up to learn how to re-identify these kinds: here's a "cat" again, here's a cat again, and here's a case of reference again. One of the regularities these kinds participate in, and thus one way of re-identifying them, is that "cat" is used to refer to cats. Learning this fact will result from the general (essentialist driven) push to learn to re-identify each of these sources of correlation. In doing so, the general cognitive strategy will be to make use of whatever cues are available to help re-identify "cat"s, cats, and instances of reference. (Note that the learner need not possess any deep knowledge of the essences or individuative principles underlying the things it learns about, a possibility that Bloom acknowledges for some things [e.g. particular kinds, p. 168] but, puzzlingly, not others [e.g. individuals vs. kinds].)
Now, it emerges very clearly from Bloom's book how resourceful children are in learning words. It seems that if there is a valid cue available - whether artifact function, shape, substance, spatio-temporal history, others' intentions, object coherence, familiarity, importance, or syntactic context - at some point in her development, a child will make use of it. (Most of the cues Bloom rules out would actually constitute very poor evidence for what a word means.) This is just what one would expect if the above general purpose learning story were true.
All that is left to worry the empiricist is the apparent belief in essentialism that drives the whole process. We have proposed that there is no such belief, but rather that this cognitive habit emerges from a simple circuit that forms the basic building block for the entire cortical network (Ryder & Favorov, 2001; Favorov & Ryder, submitted).