 Summary. Descartes provides one of the first purely psychological uses of the concept of consciousness when he defines thought in terms of consciousness. However, he does not provide an analysis of the concept. Rather, he employs the concept in a way that grounds his epistemic claims in the Meditations, for example. But the ways in which he employs the concept is suggestive of an analysis: a conscious thought is a mental state that is somehow self-intimating. And all thoughts, according to Descartes, have this basic property.