Intuition is the undoubting conception of a pure and attentive mind, which arises from the light of reason alone, and is more certain than deduction.
Rene DescartesWhen I consider this carefully, I find not a single property which with certainty separates the waking state from the dream. How can you be certain that your whole life is not a dream?
Rene DescartesIt is to the body alone that we should attribute everything that can be observed in us to oppose our reason.
Rene Descartes