Defining aphasia: Some theoretical and clinical implications of operating from a formal definition

Abstract Theoretical and philosophical issues related to the need for and criteria of a formal definition of aphasia are discussed. Following a review of several definitions of aphasia and the contrast of two, a formal definition is advanced that meets the specific requirements of a scientific definition: criteria for group membership and the assumed mechanisms for these criteria. The specific criteria for group membership are discussed and the assumed mechanisms are presented. It is argued that this definition (or a well justified alternative) can serve as a first approximation to a general theory of aphasia. It is also claimed that it can inform the research consumer about important but unstated assumptions of researchers as well as provide clinical guidance.