The problem of prototypicality
The third problem with the definitional view of categories is related to the problem of conceptual fuzziness, but while the problem of conceptual fuzziness concerns what happens at the boundaries of a category, the problem of prototypicality concerns what happens at the center of a category. As we will see in the next section, findings from experimental cognitive psychology reveal that categories give rise to prototype or typicality effects. For example, while people judge TABLE or CHAIR as ‘good examples’ or ‘typical examples’ of the category FURNITURE, CARPET is judged as a less good example. These asymmetries between category members are called typicality effects. While we might expect this to happen in the case of categories that have fuzzy boundaries, experiments have revealed that categories with distinct boundaries also show typicality effects. For example, Armstrong et al. (1983) found that the category EVEN NUMBERS exhibits typicality effects: participants in their experiments consistently rated certain members of the category including ‘2’, ‘4’, ‘6’, and ‘8’ as ‘better’ examples of the category than, say, ‘98’ or ‘10,002’. Categories that exhibit typicality effects are called graded categories. Typicality effects represent a serious challenge for the classical theory, because if each member of a category shares the same definitional structure, then each member should be equally ‘typical’. These problems with the classical theory of categorisation are summarised in Table 8.2.
Further problems
Laurence and Margolis (1999) discuss further problems with this approach which we mention only briefly here. These are what they call the problem of psychological reality and the problem of ignorance and error.
The problem of psychological reality relates to the fact that there is no evidence for definitional structure in psychological experiments. For example, we might expect words with a relatively ‘simple’ definitional structure or small set of features (like, say, man) to be recognised more rapidly in word-recognition experiments than words with a more ‘complex’ definitional structure or greater number of features (like, say, cousin). This expectation is not borne out by experimental evidence. The problem of ignorance and error relates to the fact that it is possible to possess a concept without knowing what its properties are. In other words, possessing a concept is not dependent upon knowing its definition. For example, it is possible to have the concept WHALE while mistakenly believing that it belongs to the category FISH rather than the category MAMMAL.
