A detailed investigation of the pragmatic factors which determine the appropriateness of definite article usage (specifically of the non-generic uses of the definite article in English). The 'location theory' of definiteness is proposed: the use of thedefinite article acts as an instruction to the hearer to locate the referent of the noun phrase within one of a number of sets of objects which are pragmatically defined by different types of shared knowledge and the situation of utterance.