Teach a man to read and write, and you have put into his hands the great keys of the wisdom-box.

The man who is all morality and intellect, although he may be good and even great, is, after all, only half a man.

The only objections that have occurred to me are, 1st that you have loaded yourself with an unnecessary difficulty in adopting Natura non facit saltum so unreservedly. . . . And 2nd, it is not clear to me why, if continual physical conditions are of so little moment as you suppose, variation should occur at all. However, I must read the book two or three times more before I presume to begin picking holes.

It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.

In scientific work, those who refuse to go beyond fact rarely get as far as fact.

The very existence of society depends on the fact that every member of it tacitly admits he is not the exclusive possessor of himself, and that he admits the claim of the polity of which he forms a part, to act, to some extent, as his master.

[Scientists] have learned to respect nothing but evidence, and to believe that their highest duty lies in submitting to it however it may jar against their inclinations.