The philosophy of reasoning, to be complete, ought to comprise the theory of bad as well as of good reasoning.

When a thing is bought not for its use but for its costliness, cheapness is no recommendation. As Sismondi remarks, the consequence of cheapening articles of vanity, is not that less is expended on such things, but that the buyers substitute for the cheapened article some other which is more costly, or a more elaborate quality of the same thing; and as the inferior quality answered the purpose of vanity equally well when it was equally expensive, a tax on the article is really paid by nobody: it is a creation of public revenue by which nobody loses.

There is a limit to the legitimate interference of collective opinion with individual independence: and to find that limit, and maintain it against encroachment, is as indispensable to a good condition of human affairs, as protection against political despotism.

He must be able to hear them [the counter arguments] from persons who actually believe them; who defend them in earnest, and do their very utmost for them. He must know them in their most plausible and persuasive form; he must feel the whole force of the difficulty which the true view of the subject has to encounter and dispose of; else he will never really possess himself of the portion of truth which meets and removes that difficulty.

There is always need of persons not only to discover new truths, and point out when what were once truths are true no longer, but also to commence new practices, and set the example of more enlightened conduct, and better taste and sense in human life.

Human beings are not like sheep; and even sheep are not undistinguishably alike. A man cannot get a coat or a pair oboots to fit him, unless they are either made to his measure, or he has a whole warehouseful to choose from: and is it easier to fit him with a life than with a coat, or are human beings more like one another in their whole physical and spiritual conformation than in the shape of their feet? If it were only that people have diversities of taste, that is reason enough for not attempting to shape them all after one model.

In the human mind, one-sidedness has always been the rule, and many-sidedness the exception. Hence, even in revolutions of opinion, one part of the truth usually sets while another rises.