The desire to understand the world and the desire to reform it are the two great engines of progress, without which human society would stand still or retrogress.

Modern life cannot be constructed on . . . physically strenuous principles. A great deal of work is sedentary, and most manual work exercises only a few specialized muscles.

Science, by itself, cannot supply us with an ethic. It can show us how to achieve a given end, and it may show us that some ends cannot be achieved.

A man who has once perceived, however temporarily and however briefly, what makes greatness of soul, can no longer be happy if he allows himself to be petty, self-seeking, troubled by trivial misfortunes, dreading what fate may have in store for him. The man capable of greatness of soul will open wide the windows of his mind, letting the winds blow freely upon it from every portion of the universe.

The moral thing I should wish to say to them is very simple; I should say: "Love is wise - Hatred is foolish." In this world, which is getting more and more closely interconnected, we have to learn to tolerate each other.

Science seems to be at war with itself.... Naive realism leads to physics, and physics, if true, shows naive realism to be false. Therefore naive realism, if true, is false; therefore it is false.

Reason may be a small force, but it is constant, and works always in one direction, while the forces of unreason destroy one another in futile strife.