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

Your joy is your sorrow unmasked. And the self-same well from which your laughter rises was often-times filled with your tears.

It is only prudent never to place complete confidence in that by which we have even once been deceived.

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

The greatest minds are capable of the greatest vices as well as of the greatest virtues.

I think; therefore I am.

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

The first precept was never to accept a thing as true until I knew it as such without a single doubt.

One cannot conceive anything so strange and so implausible that it has not already been said by one philosopher or another.

Nothing is more fairly distributed than common sense - no one needs more of it than one already has

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.

It is not enough to have a good mind the main thing is to use it well.

Cogito, ergo, sum. (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.

Cogito ergo sum.

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

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

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.

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.