"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."
"Except our own thoughts, there is nothing absolutely in our power."
"Let whoever can do so deceive me, he will never bring it about that I am nothing, so long as I continue to think I am something."
"Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it."
"I think; therefore I am."
"I hope that posterity will judge me kindly, not only as to the things which I have explained, but also to those which I have intentionally omitted so as to leave to others the pleasure of discovery."