Delight at having understood a very abstract and obscure system leads most people to believe in the truth of what it demonstrates.

Man is a masterpiece of creation, if only because no amount of determinism can prevent him from believing that he acts as a free being.

A good method of discovery is to imagine certain members of a system removed and then see how what is left would behave: for example, where would we be if iron were absent from the world: this is an old example.

We are obliged to regard many of our original minds as crazy at least until we have become as clever as they are.

To err is human also in so far as animals seldom or never err, or at least only the cleverest of them do so.

Pain warns us not to exert our limbs to the point of breaking them. How much knowledge would we not need to recognize this by the exercise of mere reason.

Why does a suppurating lung give so little warning and a sore on the finger so much?