"I can easily conceive that there is nothing in the world, that there is no heaven, no earth, no minds, no bodies; is it not then likewise true that I do not exist?"

"The existence of God is a necessary consequence of my idea of God."

"I have long ago observed that in order to study the truth, it is necessary once in the course of our life to demolish everything completely and start again from the foundations."

"It is precisely because I am in the habit of using my senses to think of things that I find it difficult to think of anything else."

"The mind is a substance whose whole essence or nature is to think, and which needs no place, nor depends on any material thing, in order to exist."