I think; therefore I am.
The reading of all good books is like conversation with the finest men of past centuries.
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.
Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it.
I suppose therefore that all things I see are illusions; I believe that nothing has ever existed of everything my lying memory tells me. I think I have no senses. I believe that body, shape, extension, motion, location are functions. What is there then that can be taken as true? Perhaps only this one thing, that nothing at all is certain.
And thus, the actions of life often not allowing any delay, it is a truth very certain that, when it is not in our power to determine the most true opinions we ought to follow the most probable.
Doubt is the origin of wisdom.
Conquer yourself rather than the world.
It is not enough to have a good mind; the main thing is to use it well.
Except our own thoughts, there is nothing absolutely in our power.
The greatest minds are capable of the greatest vices as well as of the greatest virtues.