that is, one that doubts, affirms, denies, understands a few things, is ignorant of many others, wills this and not that, and also imagines and perceives by the senses; for as I have already remarked, although the things I perceive or imagine outside myself do not perhaps exist, yet I am certain that the modes of thinking that I call sensations and imaginations, considered purely and simply as modes of thinking, do exist inside me.