The perpetual obstacle to human advancement is custom.

... 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.

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

It is conceivable that religion may be morally useful without being intellectually sustainable.

In all intellectual debates, both sides tend to be correct in what they affirm, and wrong in what they deny.

A state which dwarfs its men, in order that they may be more docile instruments in its hands even for beneficial purposes--will find that with small men no great thing can really be accomplished.

It is not the feeling sure of a doctrine (be it what it may) which I call an assumption of infallibility. It is the undertaking to decide that question for others, without allowing them to hear what can be said on the contrary side. And I denounce and reprobate this pretension not the less, if put forth on the side of my most solemn convictions.