Full Idea
Because waking I often observe the absurdity of dreams, but never dream of the absurdity of my waking thoughts, I am well satisfied that, being awake, I know I dream not, though when I dream I think myself awake.
Gist of Idea
Dreams must be false because they seem absurd, but dreams don't see waking as absurd
Source
Thomas Hobbes (Leviathan [1651], 1.02)
Book Reference
Hobbes,Thomas: 'Leviathan', ed/tr. Macpherson,C.B. [Penguin 1981], p.90