  What role does consciousness play in Descartes' theory of mind? Many scholars believe that, for Descartes, consciousness is the defining property of mind (e.g., Rozemond 2006). There is some support for this position in the Second Replies. There Descartes defines mind as “the substance in which thought immediately resides” (7:161). He says of the term “thought” that it extends to “everything that is within us in such a way that we are immediately conscious of it” (7:160*). If mind is thinking substance and thoughts are essentially conscious, perhaps consciousness is the essence of thought?