Except our own thoughts, there is nothing absolutely in our... - René Descartes

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

"There is nothing more ancient than the truth."

"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."

"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."

"The reading of all good books is like conversation with the finest men of past centuries."