Most philosophers in the High Middle Ages agreed that what we immediately perceive are external objects. Yet most philosophers in the High Middle Ages also held, following Aristotle, that perception is a process wherein the perceiver takes on the form or likeness of the external object. This form or likeness — called a species — is a representation by means of which we immediately perceive the external object. Thomas Aquinas defended this thesis in one form, and Durand of St.-Pourçain, his Dominican successor, rejects it. This paper explores Durand's novel criticism of Aquinas's species-theory of cognition. I first develop and defend a new interpretation of Durand's central criticism of Aquinas's theory of cognition. I close with some considerations about Durand's alternative to the theory.