I am indeed amazed when I consider how weak my mind is and how prone to error.

Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency.

Bad books engender bad habits, but bad habits engender good books.

It is to the body alone that we should attribute everything that can be observed in us to oppose our reason.

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.

Conquer yourself rather than the world.

All is to be doubted.