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.

Many intelligent people, when about to write . . . , force on their minds a certain notion about style, just as they screw up their faces when they sit for their portraits.

God creates the animals, man creates himself.

The book which most deserved to be banned would be a catalog of banned books.

Great men too make mistakes, and many among them do it so often that one is almost tempted to call them little men.

The wisdom of providence is as much revealed in the rarity of genius, as in the circumstance that not everyone is deaf or blind.

One is rarely an impulsive innovator after the age of sixty, but one can still be a very fine orderly and inventive thinker. One rarely procreates children at that age, but one is all the more skilled at educating those who have already been procreated, and education is procreation of another kind.