Science is the acceptance of what works and the rejection of what does not. That needs more courage than we might think.

We have to understand that the world can only be grasped by action, not by contemplation. The hand is more important than the eye ... The hand is the cutting edge of the mind.

The Principle of Tolerance, fixed once for all the realization that all knowledge is limited. It is an irony of history that at the very time when this was being worked out, there should rise, under Hitler in Germany and other tyrants elsewhere, a counter-conception: a principle of monstrous certainty. When the future looks back on the 1930's, it will think of them as a crucial confrontation of culture as I have been expounding it - the ascent of man against the throwback to the despots' belief that they have absolute certainty.

Dissent is the mark of freedom, as originality is the mark of independence of mind. … No one can be a scientist … if he does not have independence of observation and of thought.

By the worldly standards of public life, all scholars in their work are of course oddly virtuous. They do not make wild claims, they do not cheat, they do not try to persuade at any cost, they appeal neither to prejudice nor to authority, they are often frank about their ignorance, their disputes are fairly decorous, they do not confuse what is being argued with race, politics, sex or age, they listen patiently to the young and to the old who both know everything. These are the general virtues of scholarship, and they are peculiarly the virtues of science.

The human baby, the human being, is a mosaic of animal and angel.

One aim of physical sciences had been to give an exact picture the material world. One achievement of physics in the twentieth century has been to prove that that aim is unattainable.