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.

The beliefs which we have most warrant for, have no safeguard to rest on, but a standing invitation to the whole world to prove them unfounded.

The despotism of custom is everywhere the standing hindrance to human advancement.

Mankind are greater gainers by suffering each other to live as seems good to themselves, than by compelling each to live as seems good to the rest.

The best state for human nature is that in which, while no one is poor, no one desires to be richer, nor has any reason to fear from thrust back, by the efforts of others to push themselves forward.

He who knows only his own side of the case (argument) knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion

... All ideas need to be heard, because each idea contains one aspect of the truth. By examining that aspect, we add to our own idea of the truth. Even ideas that have no truth in them whatsoever are useful because by disproving them, we add support to our own ideas.