Here I beg you to observe in passing that the scruples that prevented ancient writers from using arithmetical terms in geometry, and which can only be a consequence of their inability to perceive clearly the relation between these two subjects, introduced much obscurity and confusion into their explanations.

The entire method consists in the order and arrangement of the things to which the mind's eye must turn so that we can discover some truth.

There is a little gland in the brain in which the soul exercises its functions in a more particular way than in the other parts.

I am thing that thinks: that is, a things that doubts,affirms, denies, understands a few things, is ignorant of many things, is willing, is unwilling, and also which imagines and has sensory perceptions.

Each problem that I solved became a rule, which served afterwards to solve other problems.

Science is practical philosophy.

Every man is indeed bound to do what he can to promote the good of others, and a man who is of no use to anyone is strictly worthless.