René Descartes

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

"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."

"But in my opinion, all things in nature occur mathematically."

"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."

"Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it."

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

"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."

"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."

"There is nothing more ancient than the truth."

"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."

"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."

"I think; therefore I am."