Abstract

The principle of compositionality is a statement about the semantics of expressions. It can also be framed slightly differently so that it becomes a principle about the content of complex concepts. This article explains this principle, and the reasons for deviating from it. It will review the psychological research on typicality effects and non-logical reasoning which suggest that explanations can be given for significant phenomena if concepts are understood as prototypes. The evidence suggests that the combination of prototypes follows a principle corresponding to something like PC' rather than PC. PC' states that the content of a complex concept is completely determined by the contents of its parts and their mode of combination, together with general knowledge. A prototype representation of the conjunctive concept is formed by aggregating one feature with another. Any instance is then judged to belong in the conjunction on the basis of its overall similarity to this composite representation.