Rosch (1976) has proposed an alternative to the view that concepts are com¬posed from sets of features which necessarily and sufficiently define instances of a concept. Rosch proposes that concepts are best viewed as prototypes: a ‘bird’ is not best defined by reference to a set of features that refer to such matters as wings, warm-bloodedness, and egg-laying characteristics, but rather by reference to typical instances, so that a ‘prototypical bird’ is something more like a robin than it is like a toucan, penguin, ostrich, or even eagle. This is the theory of prototypes. As we saw in the preceding section, individuals do have ideas of typical instances of colors, and these ideas are remarkably similar among vari¬ous cultural groups. Such similarity in views, however, is found not only in reference to birds and colors.
A variety of experiments has shown that people do in fact classify quite consistently objects of various kinds according to what they regard as being typical instances; for example, (1) furniture, so that, whereas a chair is a typical item of furniture, an ashtray is not; (2) fruit, so that, whereas apples and plums are typical, coconuts and olives are not; and (3) clothing, so that, whereas coats and trousers are typical items, things like bracelets and purses are not (Clark and Clark, 1977, p. 464). The remarkably uniform behavior that people exhibit in such tasks cannot be accounted for by a theory which says that concepts are formed from sets of defining features. Such a theory fails to explain why some instances are consistently held to be more typical or central than others when all exhibit the same set of defining features.
Hudson (1996, pp. 75-8) believes that prototype theory has much to offer sociolinguists. He believes it leads to an easier account of how people learn to use language, particularly linguistic concepts, from the kinds of instances they come across. He says (p. 77) that:
a prototype-based concept can