The spirit of improvement is not always a spirit of liberty, for it may aim at forcing improvements on an unwilling people.

On religion in particular, the time appears to me to have come, when it is a duty of all who, being qualified in point of knowledge, have, on mature consideration, satisfied themselves that the current opinions are not only false, but hurtful, to make their dissent known.

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

All errors which a man is likely to commit against advice are far outweighed by the evil of allowing others to constrain him for his good.

if any opinion is compelled to silence, that opinion may, for aught we can certainly know, be true. To deny this is to assume our own infallibility.

A profound conviction raises a man above the feeling of ridicule.

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.