The future is always present, as a promise, a lure and a temptation.

Science may be described as the art of systematic over-simplification.

Better our hypotheses die for our errors than ourselves.

Science is perhaps the only human activity in which errors are systematically criticized and, in time, corrected.

. . . it seems to me certain that more people are killed out of righteous stupidity than out of wickedness.

The war of ideas is a Greek invention. It is one of the most important inventions ever made. Indeed, the possibility of fighting with with words and ideas instead of fighting with swords is the very basis of our civilization, and especially of all its legal and parliamentary institutions.

The moral decisions of others should be treated with respect, as long as such decisions do not conflict with the principle of tolerance.