Out of man's mind in free play comes the creation Science. It renews itself, like the generations, thanks to an activity which is the best game of homo ludens: science is in the strictest and best sense a glorious entertainment.

The sole justification of teaching, of the school itself, is that the student comes out of it able to do something he could not do before. I say do and not know, because knowledge that doesn't lead to doing something new or doing something better is not knowledge at all.

Above all, the ability to feel the force of an argument apart from the substance it deals with is the strongest weapon against prejudice.

We cannot appreciate the art of any age without first acquiring an equivalent of the experience it depicts.

In ordinary speech the words perception and sensation tend to be used interchangeably, but the psychologist distinguishes. Sensations are the items of consciousness--a color, a weight, a texture--that we tend to think of as simple and single. Perceptions are complex affairs that embrace sensation together with other, associated or revived contents of the mind, including emotions.

Simple English is no one’s mother tongue. It has to be worked for.

The professionals resemble and recognize each other by virtue of the stigmata that their trade has left upon them. They are like the dog in the fable, whose collar has made an indelible mark around his neck. The amateur is the shaggy wolf whom no dog had better trust too far.