It often takes more courage to change one's opinion than to stick to it.

One's first step in wisdom is to question everything - and one's last is to come to terms with everything.

God creates the animals, man creates himself.

A person reveals his character by nothing so clearly as the joke he resents.

Above all things expand the frontiers of science: without this the rest counts for nothing.

The course of the seasons is a piece of clockwork, with a cuckoo to call when it is spring.

Diogenes, filthily attired, paced across the splendid carpets in Plato's dwelling. Thus, said he, do I trample on the pride of Plato. Yes, Plato replied, but only with another kind of pride.