The author presents an account of the principles shaping the morphological form of the verb. This book aims to exemplify contemporary linguistic theory. The analysis proceeds from the view that the structure of language is determined by its function as an instrument of human communication. This position breaks with sentence-based theory to return to Saussurean conception of a language as an inventory of signs. It expands the programmatic Saussurean picture by emphasizing the pervasive influence of general human psychological characteristics on both linguistic structure and language use. In contrast to sentence-based theory, sign-based theory contains no formal component of syntactic rules. It must re-characterize linguistic structure in functional, not syntactic terms.