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.

If an angel were to tell us about his philosophy, I believe many of his statements might well sound like '2 x 2= 13'.

Man loves company - even if it is only that of a small burning candle.

If nature be regarded as the teacher and we poor human beings as her pupils, the human race presents a very curious picture. We all sit together at a lecture and possess the necessary principles for understanding it, yet we always pay more attention to the chatter of our fellow students than to the lecturer's discourse. Or, if our neighbor copies something down, we sneak it from him, stealing what he himself may have heard imperfectly, and add it to our own errors of spelling and opinion.

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.

The natural scientists of the previous age knew less than we do and believed they were very close to the goal: we have taken very great steps in its direction and now discover we are still very far away from it. With the most rational philosophers an increase in their knowledge is always attended by an increased conviction of their ignorance.

A good metaphor is something even the police should keep an eye on.