The more certain existence and the better we know is indisputably ours, because, of all other objects, we possess external and superficial triable notions, while we perceive ourselves internally, deeply. What do we check then? What is, in this exceptional case, the meaning of the verb ‘to exist’?
First I see that I passage from one state to another state. I’m cold or heat, I’m happy or sad, I work or do nothing, I look around me or think about something else. Sensations, feelings, volitions, representations, such are the modifications among which distributes my existence and which color it alternately. I change, then, without ceasing. (p.13)