  Descartes denied that the senses reveal the natures of substances.  He held that in fact the human intellect is able to perceive the nature of reality through a purely intellectual perception. This means that, in order to procure the fundamental truths of metaphysics, we must “withdraw the mind from the senses” (7:4, 12, 14) and turn toward our innate ideas of the essences of things, including the essences of mind, matter, and an infinite being (God). Descartes constructed the Meditations so as to secure this process of withdrawal from the senses in Meditation I. Meditation II brings the discovery of an initial truth, in the cogito (7:25), which is elsewhere summarized as the argument “cogito, ergo sum,” or “I think, therefore I am” (7:140). Descartes observes that the cogito result is known only from the fact that it is “clearly and distinctly” perceived by the intellect (7:35). Hence, he sets up clear and distinct intellectual perception, independent of the senses, as the mark of truth (7:35, 62, 73).