Explanationbased Views Of Concepts

The theories we have reviewed so far have been quite successful in accounting for the evidence of typicality effects, prediction effects, and other results involving object concepts. However, these theories still find some pieces of evidence hard to explain (e.g., concept instability effects). One remedy for this deficiency is to suggest that more complex formulations of knowledge than attribute lists are required (see Putnam, 1975a, b, for arguments in philosophy on this point). In Chapter 9, we saw how a variety of more complex, structured representations clearly reside in memory (e.g., schemata and scripts).

Initially, in this chapter, we introduced three guiding constraints for conceptual systems; informativeness, economy, and coherence. In attribute-based theories, concepts cohere because members of a category have similar attributes. However, there are concepts that have little similarity between their attributes. We have already seen how Barsalou's (1983) ad hoc categories upset this view of coherence (e.g., the category of things-to-sell-in-a-garage-sale). As mentioned earlier, Murphy and Medin (1985) point out that in the Bible, the dietary rules associated with the abominations of Leviticus produce the categories of clean and unclean animals. What is it that makes camels, ostriches, crocodiles, mice, sharks, and eels unclean, and gazelles, frogs, most fish, grasshoppers, and some locusts clean? Murphy and Medin argued that it was not the similarity of members of the concepts that determined the conceptual distinction but some theory or explanatory framework. The concept of clean and unclean animals rests on a theory of how the features of habitat, biological structure, and form of locomotion should be correlated in various animals (see Douglas, 1966). Roughly speaking, creatures of the water should have fins, scales, and swim, and creatures of the land should have four legs. If a creature conforms with this theory, then it is considered clean. But, any creature that is not equipped for the right kind of locomotion is considered unclean (e.g., ostriches).

Murphy and Medin's notion of a theory refers to any of a number of mental "explanations" (rather than a complete scientific account): for example, "causal knowledge certainly embodies a theory of certain phenomena; scripts may contain an implicit theory of entailment between mundane events; knowledge of rules embodies a theory of the relations between rule constituents;

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