  Descartes in fact did hold that all thoughts are, in some way, conscious (7:226). He did not mean by this that we have reflective awareness of, and can remember, every thought that we have (5:220). In the Second Meditation, he describes himself as a thinking thing by enumerating all the modes of thoughts of which he is conscious: understanding (or intellection), willing, imagining, and (at this point, at least seeming to have) sense perceptions (7:28). He thus sets up consciousness as a mark of thought. But is it the essence? There is another possibility. If perception (intellection, representation) is the essence of thought, then all thoughts might be conscious in a basic way because the character of the intellectual substance is to represent, and any representation present in an intellectual substance is thereby conscious. Similarly, any act of will present in an intellectual substance also is available to consciousness, because it is of the essence of such a substance to perceive its own states (11:343). Accordingly, perception or representation is the essence of mind, and consciousness follows as a result of the mind's being a representing substance.