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.

I know that I exist; the question is, What is this 'I' that 'I' know.

[About Pierre de Fermat] It cannot be denied that he has had many exceptional ideas, and that he is a highly intelligent man. For my part, however, I have always been taught to take a broad overview of things, in order to be able to deduce from them general rules, which might be applicable elsewhere.

I can doubt everything, except one thing, and that is the very fact that I doubt. Simply put - I think, therefore I am

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

Common sense is the most fairly distributed thing in the world, for each one thinks he is so well-endowed with it that even those who are hardest to satisfy in all other matters are not in the habit of desiring more of it than they already have.

I was convinced that our beliefs are based much more on custom and example than on any certain knowledge.