Rene Descartes

Except our own thoughts, there is nothing absolutely in our power.

I think; therefore I am.

Good sense is, of all things among men, the most equally distributed: for every one thinks himself so abundantly provided with it, that those even who are the most difficult to satisfy in everything else, do not usually desire a larger measure of this quality than they already possess.

The reading of all good books is indeed like a conversation with the noblest men of past centuries who were the authors of them, nay a carefully studied conversation, in which they reveal to us none but the best of their thoughts.

In order to improve the mind, we ought less to learn, than to contemplate.

I know not if I was then a man dreaming I was a butterfly, or if I am now a butterfly dreaming I am a man.

Cogito ergo sum. (I think; therefore I am.)

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

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.