This study deals with the interpretation of verbal commands for action. After an experimental study of human interpretation of instructions for drawing geometrical figures, we have devised a model whose computerized version is called SIROCO. This model represents an attempt to simulate category construction for interpretation. The use of fuzzy logic and circumstantial semantic networks allows emphasizing the importance the situation plays in completing and clarifying propositions expressed in natural language. Finally, a simulation shows quite good results for the model.