There is one thing in the world more wicked than the desire to command, and that is the will to obey.

When an action is once done, it is right or wrong for ever; no accidental failure of its good or evil fruits can possibly alter that.

The danger to society is not merely that it should believe wrong things, though that is great enough; but that it should become credulous, and lose the habit of testing things and inquiring into them; for then it must sink back into savagery.

He who truly believes that which prompts him to an action has looked upon the action to lust after it, he has committed it already in his heart.

To know all about anything is to know how to deal with it under all circumstances.

The scientific discovery appears first as the hypothesis of an analogy; and science tends to become independent of the hypothesis.

Remember that [scientific thought] is the guide of action; that the truth which it arrives at is not that which we can ideally contemplate without error, but that which we may act upon without fear; and you cannot fail to see that scientific thought is not an accompaniment or condition of human progress, but human progress itself.