The theoretical idea ... does not arise apart from and independent of experience; nor can it be derived from experience by a purely logical procedure. It is produced by a creative act. Once a theoretical idea has been acquired, one does well to hold fast to it until it leads to an untenable conclusion.

It is difficult to say what truth is, but sometimes it is so easy to recognize a falsehood.

We must be prepared to make the same heroic sacrifices for the cause of peace that we make ungrudgingly for the cause of war.

You never fail until you stop trying.

My success wasn't so much due to intelligence, but the fact that I stuck with problems longer.

Even a fool is wise after an event.

It stands to the everlasting credit of science that by acting on the human mind it has overcome man's insecurity before himself and before nature.