really mattered if people who tell dreams "really had these images while they slept, or whether it merely seems so to them on waking". He argues that the sentence "I am asleep" is a senseless form of words; that dreams cannot exist independently of the waking impression; and that skepticism based on dreaming "comes from confusing the historical and dream telling senses...[of]...the past tense" (page 120). In the chapter: "Do I Know I Am Awake ?" he argues that we do not have to say: "I know that I am awake" simply because it would be absurd to deny that one is awake. The dream hypothesis is also used to develop other philosophical concepts, such as Valberg's personal horizon: what this world would be internal to if this were all a dream. See also Cartesian doubt Consensus reality Evil demon False awakening Maya (illusion) Multiverse Reality in Buddhism Simulated reality Social simulation Solipsism Notes References Malcolm, N. (1959) Dreaming London: Routledge & Kegan Paul, 2nd Impression 1962. Epistemology Academic skepticism Arguments in philosophy of mind Internalism and externalism Reality Skepticism Science fiction themes Philosophical paradoxes