 Further, like Descartes, Locke argues that this is the essence of thought—one can’t have a thought without “being conscious of it” (2.1.19). However, he will extend this idea only as far as experience will allow—it is not at all clear to him that “the soul always thinks,” since we often fail to have conscious experience while asleep. And so, as Locke says, “every drowsy nod shakes their doctrine, who teach that the soul is always thinking” (2.1.13; see 2.1.10–20 for the full argument). This argument resembles that offered by Cudworth, and, like Cudworth, Locke will conclude that thinking is not the essence of the soul. The soul can persist through a state in which there is no thinking—this is the beginning of his separation of the underlying substance from its psychological states. The consciousness of an individual bears no necessary relation to the substance it inheres in, and so the substance contributes nothing to the identity of the individual. 