A common theory of the interpretation of indefinite noun phrases is that they introduce new entities into the discourse. This, however, seems problematic if the indefinite NP occurs in an imperative context, since the command is to be carried out on an object already present in the physical context. We present a solution to this apparent problem using a theory of intensional knowledge representation within the architecture of a natural language understanding computational agent, which we have implemented. The agent creates a new intensional entity for the indefinite NP, but when, in the course of carrying out the command, it recognizes the object it is performing the command on, it considers the new entity and its previous conception of the object to be coextensional. This approach is consistent with, but different from, several previous analyses of this situation.