The highest level than can be reached by a mediocre but experienced mind is a talent for uncovering the weaknesses of those greater than itself.

One has to do something new in order to see something new.

Man is a masterpiece of creation if for no other reason than that, all the weight of evidence for determinism notwithstanding, he believes he has free will.

Nothing makes one old so quickly as the ever-present thought that one is growing older.

Some people feel with their heads and think with their hearts.

As nations improve, so do their gods.

The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.