I believe that whatever we do or live for has its causality; it is good, however, that we cannot see through to it.

The measure of intelligence is the ability to change.

[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.

As a human being, one has been endowed with just enough intelligence to be able to see clearly how utterly inadequate that intelligence is when confronted with what exists.

Great spirits often meet violent oppisition with mediocre minds.

Every day I remind myself that my inner and outer life are based on the labors of other men, living and dead, and that I must exert myself in order to give in the same measure as I have received and am still receiving.

You have to learn the rules of the game. And then you have to play better than anyone else.