Man's maturity: to have regained the seriousness that he had as a child at play.

God is dead, but considering the state the species man is in, there will perhaps be caves, for ages yet, in which his shadow will be shown.

There are no beautiful surfaces without a terrible depth.

We have no dreams at all or interesting ones. We should learn to be awake the same way- not at all or in an interesting manner

It is perhaps just dawning on five or six minds that physics, too, is only an interpretation and exegesis of the world (to suit us, if I may say so!) and not a world-explanation.

With regard to philosophical metaphysics, I always see increasing numbers who have attained to the negative goal, but as yet few who climb a few rungs backwards; one ought to look out, perhaps, over the last steps of the ladder, but not try to stand upon them.

You say it is the good cause that hallows even war? I say unto you: it is the good war that hallows any cause.