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 greatest minds are capable of the greatest vices as well as of the greatest virtues.
Everything is self-evident.
When it is not in our power to follow what is true, we ought to follow what is most probable.
The first precept was never to accept a thing as true until I knew it as such without a single doubt.
There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.