In Descartes' Meditations on the First Philosophy, his "First Meditation" focuses on phenomenon that can be called into doubt. In this section, Descartes proceeds to discuss reality and illusion, and the questions these thoughts raise.
In the paragraph that begins with the line: "a brilliant piece of reasoning!," Descartes analyzes or draws connections between humans who are sane and insane, and sleep and dreams versus wakefulness and reality. In this paragraph, Descartes posits that a person whom, in insanity, has visions and hallucinations can be comparable to a person whom, in dreams, has similar visions and experiences. Furthermore, Descartes continues to note that the occurrences a person has in wakefulness perhaps can not be distinguished from the occurrences a person has in dreams. He states that (while awake): "I stretch out and feel my hand I do so deliberately, and I know what I am doing. …
