"I have never made any distinction between the sciences, but have always held that all are linked together, and that it is easier to learn them all at once than to learn one separately."

"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 power of judging well and of distinguishing the true from the false, which is properly what is called good sense or reason, is by nature equal in all men."

"To be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it."

"The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, the kno…"