No matter how eloquently a dog may bark, he cannot tell you that his parents were poor, but honest.

Few people can be happy unless they hate some other person, nation, or creed.

Dogma demands authority, rather than intelligent thought, as the source of opinion; it requires persecution of heretics and hostility to unbelievers; it asks of its disciples that they should inhibit natural kindliness in favor of systematic hatred.

But as the work proceeded I was continually reminded of the fable about the elephant and the tortoise. Having constructed an elephant upon which the mathematical world could rest, I found the elephant tottering, and proceeded to construct a tortoise to keep the elephant from falling. But the tortoise was not more secure than the elephant, and after some twenty years of very arduous toil, I came to the conclusion that there was nothing more that I could do in the way of making mathematical knowledge indubitable.

One is always a little afraid of love, but above all, one is afraid of pain or causing pain.

There is no excuse for deceiving children. And when, as must happen in conventional families, they find that their parents have lied, they lose confidence in them and feel justified in lying to them.

To be happy in this world, especially when youth is past, it is necessary to feel oneself not merely an isolated individual whose day will soon be over, but part of the stream of life flowing on from the first germ to the remote and unknown future.