This paper describes a computational model of concept acquisition for natural language. W e develop a theory of lexical semantics, the Eztended Aspect Calculus, which together with a ~maxkedness theory" for thematic relations, constrains what a possible word meaning can be. This is based on the supposition that predicates from the perceptual domain axe the primitives for more abstract relations. W e then describe an implementation of this model, TULLY, which mirrors the stages of lexical acquisition for children. .
