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.

We often hear the teachers of all creeds lamenting the difficulty of keeping up in the minds of believers a lively apprehension of the truth which they nominally recognize, so that it may penetrate the feelings, and acquire a real mastery over the conduct.... When it has come to be a hereditary creed, and to be received passively, not actively ... there is a progressive tendency to forget all of the belief except the formularies ... until it almost ceases to connect itself at all with the inner life of the human being.

the only way in which a human being can make some approach to knowing the whole of a subject, is by hearing what can be said about it by persons of every variety of opinion, and studying all modes in which it can be looked at by every character of mind. No wise man ever acquired his wisdom in any mode but this; nor is it in the nature of human intellect to become wise in any other manner.

This is what writers mean when they say that the notion of cause involves the idea of necessity. If there be any meaning which confessedly belongs to the term necessity, it is unconditionalness. That which is necessary, that which must be, means that which will be, whatever supposition we may make in regard to all other things.

Complete liberty of contradicting and disproving our opinion, is the very condition which justifies us in assuming its truth for purposes of action.

A [psychological] difficulty is not an impossibility.

It is useful that while mankind are imperfect there should be different opinions, so is it that there should be different experiments of living; that free scope should be given to varieties of character, short of injury to others.