René Descartes

• Cogito ergo sum. (I think, therefore I am.)
• Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it.
• Conquer yourself rather than the world.
• Divide each difficulty into as many parts as is feasible and necessary to resolve it.
• Except our own thoughts, there is nothing absolutely in our power.
• 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.
• 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.
• It is not enough to have a good mind; the main thing is to use it well.
• The greatest minds are capable of the greatest vices as well as of the greatest virtues.
• The reading of all good books is like conversation with the finest men of past centuries.
• There is nothing more ancient than the truth.