The method of scientific investigation is nothing but the expression of the necessary mode of working of the human mind.

What are the moral convictions most fondly held by barbarous and semi-barbarous people? They are the convictions that authority is the soundest basis of belief; that merit attaches to readiness to believe; that the doubting disposition is a bad one, and skepticism is a sin.

If a little knowledge is dangerous, where is the man who has so much as to be out of danger?

It is one of the most saddening things in life that, try as we may, we can never be certain of making people happy, whereas we can almost always be certain of making them unhappy.

The only question which any wise man can ask himself, and which any honest man will ask himself, is whether a doctrine is true or false.

The population question is the real riddle of the sphinx, to which no political Oedipus has as yet found the answer. In view of the ravages of the terrible monster over-multiplication, all other riddle sink into insignificance.

My belief is that no human being or society composed of human beings ever did or ever will come to much unless their conduct was governed and guided by the love of some ethical ideal.