When a book and a head collide and a hollow sound is heard, must it always have come from the book?

The great trick of regarding small departures from the truth as the truth itself - on which is founded the entire integral calculus - is also the basis of our witty speculations, where the whole thing would often collapse if we considered the departures with philosophical rigour.

Great men too make mistakes, and many among them do it so often that one is almost tempted to call them little men.

The proof that man is the noblest of all creatures is that no other creature has ever denied it.

Some theories are good for nothing except to be argued about.

The most perfect ape cannot draw an ape; only man can do that; but, likewise, only man regards the ability to do this as a sign of superiority.

Ambition and suspicion always go together.