The Walter Burley's physics: his theory about the number of principles of generation. In terms of originality and influence, the Doctor Planus et Perspicuus was one of the most significant thinkers of the fourteenth century. In this article, I offer an introduction to the Burley's physical thinking restricted to his theory of matter and privation. Burley replaces a nominal interpretation for a real one of privation. In fact, the Burley's theory is a direct attack on Ockham's views expressed in this Expositio librorwn Physico rum. Burley answer each argument proposed by Ockham, concerning the identification of matter and privation; and he defends the view of an exaggerated realism.