“He who hid well, lived well.”

Doubt is the origin of wisdom.

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

I took especially great pleasure in mathematics because of the certainty and the evidence of its arguments.

Mind and soul of the man is entirely different from the body.

So far, I have been a spectator in this theatre which is the world, but I am now about to mount the stage, and I come forward masked.

With me, everything turns into mathematics.

In order to seek truth, it is necessary once in the course of our life to doubt, as far as possible, of all things

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

I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.

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

I think; therefore I am.

To live without philosophizing is in truth the same as keeping the eyes closed without attempting to open them.

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.

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

Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.

Nothing is made from nothing.