The only secure knowledge is that I exist.
Conquer yourself rather than the world.
There is nothing more ancient than the truth.
Each problem that I solved became a rule, which served afterwards to solve other problems.
Science is practical philosophy.
The nature of matter, or body considered in general, consists not in its being something which is hard or heavy or coloured, or which affects the senses in any way, but simply in its being something which is extended in length, breadth and depth.