Truth emerges from the clash of adverse ideas.

To refuse a hearing to an opinion, because they are sure that it is false, is to assume that their certainty is the same thing as absolute certainty. All silencing of discussion is an assumption of infallibility.

Over one's mind and over one's body the individual is sovereign.

Lord, enlighten thou our enemies. Sharpen their wits, give acuteness to their perceptions, and consecutiveness and clearness to their reasoning powers: we are in danger from their folly, not from their wisdom; their weakness is what fills us with apprehension, not their strength.

The amount of eccentricity in a society has generally been proportional to the amount of genius, mental vigor, and moral courage it contained. That so few now dare to be eccentric marks the chief danger of the time.

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.

The process of tracing regularity in any complicated, and at first sight confused, set of appearances, is necessarily tentative; we begin by making any supposition, even a false one, to see what consequences will follow from it ; and by observing how these differ from the real phenomena, we learn what corrections to make in our assumption.