If you would be a real seeker after truth, it is necessary t... - René Descartes
"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."
More quotes by René Descartes
"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."
"There is nothing more ancient than the truth."
"I think; therefore I am."
"But in my opinion, all things in nature occur mathematically."