This is what writers mean when they say that the notion of cause involves the idea of necessity. If there be any meaning which confessedly belongs to the term necessity, it is unconditionalness. That which is necessary, that which must be, means that which will be, whatever supposition we may make in regard to all other things.

Every great movement must experience three stages: ridicule, discussion, adoption.

Christian morality (so called) has all the characters of a reaction.... In its horror of sensuality, it made an idol of asceticism, which has been gradually compromised away into one of legality. It holds out the hope of heaven and the threat of hell, as the appointed and appropriate motives to a virtuous life - in this falling far below the best of the ancients, and doing what lies in it to give to human morality an essentially selfish character.... It is essentially a doctrine of passive obedience; it inculcates submission to all authorities found established.

Each undervalues that part of the materials of thought with which he is not familiar.

If opponents of all important truths do not exist, it is indispensable to imagine them and supply them with the strongest arguments which the most skillful devil's advocate can conjure up.

It's hardly possible to overstate the value, in the present state of human improvement, of placing human beings in contact with other persons dissimilar to themselves, and with modes of thought and action unlike those with which they are familiar. Such communication has always been... one of the primary sources of progress.

The successful conduct of an industrial enterprise requires two quite distinct qualifications: fidelity and zeal.