No Roman ever died in contemplation over a geometrical diagram.

I am sure that one secret of a successful teacher is that he has formulated quite clearly in his mind what the pupil has got to know in precise fashion. He will then cease from half-hearted attempts to worry his pupils with memorizing a lot of irrelevant stuff of inferior importance.

You cannot be wise without some basis of knowledge, but you may easily acquire knowledge and remain bare of wisdom.

People make the mistake of talking about 'natural laws.' There are no natural laws. There are only temporary habits of nature.

Imagination is not to be divorced from the facts. It is a way of illuminating the facts.

Some of the finest moral intuitions come to quite humble people. The visiting of lofty ideas doesn't depend on formal schooling.

Ideas won't keep. Something must be done about them.