One's work is never so bad as it appears on bad days, nor so good as it appears on good days.

If I were a medical man, I should prescribe a holiday to any patient who considered his work important.

The more we realize our minuteness and our impotence in the face of cosmic forces, the more amazing becomes what human beings have achieved.

An individual human existence should be like a river

If everything must have a cause, then God must have a cause. If there can be anything without a cause, it may just as well be the world as God, so that there cannot be any validity in that argument... The idea that things must have a beginning is really due to the poverty of our imagination.

To save the world requires faith and courage: faith in reason, and courage to proclaim what reason shows to be true.

If a Black Death could be spread throughout the world once in every generation survivors could procreate freely without making the world too full.