 Malebranche tells Arnauld that it was Augustine’s authority “which has given me the desire to put forth the new philosophy of ideas” (Malebranche [OC], 6:80). By contrast, he emphasizes in the preface of the Recherche that Augustine had failed to see that sensible qualities “are not clearly contained in the idea we have of matter,” adding that “the difference between mind and body has been known with sufficient clarity for only a few years” (Malebranche [OC], 1:20). The allusion here is to Descartes’s recent discovery of an idea of matter that reveals that its nature consists in extension alone. This idea dictates that sensible qualities such as colors, tastes and odors that are not reducible to modes of extension cannot exist external to mind. But since these qualities exist in the mind, and in particular in the mind’s perception of the qualities, the mind itself must be distinguished from body. In this way the Cartesian idea of matter reveals “the difference between mind and body.”