In living through this great epoch, it is difficult to reconcile oneself to the fact that one belongs to that mad, degenerate species that boasts of its free will. How I wish that somewhere there existed an island for those who are wise and of good will. In such a place even I should be an ardent patriot!

Combinatory play seems to be the essential feature in productive thought.

My religion consists of a humble admiration of the illimitable superior spirit who reveals himself in the slight details we are able to perceive with our frail and feeble mind.

[Kepler] had to realize clearly that logical-mathematical theoretizing, no matter how lucid, could not guarantee truth by itself; that the most beautiful logical theory means nothing in natural science without comparison with the exactest experience. Without this philosophic attitude, his work would not have been possible.

You can never solve a problem with the same kind of thinking that created the problem in the first place.

A happy man is too satisfied with the present to dwell too much on the future.

I cannot conceive of a God who rewards and punishes his [sic] creatures, or has a will of the type of which we are conscious ourselves.