A man's worst difficulties begin when he is able to do as he likes.

The foundation of morality to have done, once and for all, with lying.

Every great advance in natural knowledge has involved the absolute rejection of authority.

Perhaps the most valuable result of all education is the ability to make yourself do the thing you have to do, when it ought to be done, whether you like it or not; it is the first lesson that ought to be learned; and however early a man's training begins, it is probably the last lesson that he learns thoroughly.

It is an error to imagine that evolution signifies a constant tendency to increased perfection. That process undoubtedly involves a constant remodelling of the organism in adaptation to new conditions; but it depends on the nature of those conditions whether the directions of the modifications effected shall be upward or downward.

There is no greater mistake than the hasty conclusion that opinions are worthless because they are badly argued.