The modern world is full of the old Christian virtues gone mad. The virtues have gone mad because they have been isolated from each other and are wandering alone. Thus some scientists care for truth; and their truth is pitiless. Thus some humanitarians only care for pity; and their pity (I am sorry to say) is often untruthful.

If I did not believe in God, I should still want my doctor, my lawyer and my banker to do so.

There is not really any courage at all in attacking hoary or antiquated things, any more than in offering to fight one's grandmother. The really courageous man is he who defies tyrannies young as the morning and superstitions fresh as the first flowers. The only true free-thinker is he whose intellect is as much free from the future as from the past.

It is shorter to state the things forbidden than the things permitted; precisely because most things are permitted and only a few things forbidden.

There is no great harm in the theorist who makes up a new theory to fit a new event. But the theorist who starts with a false theory and then sees everything as making it come true is the most dangerous enemy of human reason.

All good men are international. Nearly all bad men are cosmopolitan. If we are to be international we must be national.

The telescope makes the world smaller; it is only the microscope that makes it larger.