Persecution for opinion is the master vice of society.

Love of power more frequently originates in vanity than pride (two qualities, by the way, which are often confounded) and is, consequently, yet more peculiarly the sin of little than of great minds.

We have ... dreamed so much and observed so little, that our imaginations have grown larger than the world we live in, and our judgments have dwindled down to a point.

It is in vain that we would circumscribe the power of one half of our race, and that half by far the most important and influential.

The sciences have ever been the surest guides to virtue.

He who lives in the single exercise of his mental faculties, however usefully or curiously directed, is equally an imperfect animal with the man who knows only the exercise of muscles.

Knowledge signifies things known. Where there are no things known, there is no knowledge. Where there are no things to be known, there can be no knowledge. We have observed that every science, that is, every branch of knowledge, is compounded of certain facts, of which our sensations furnish the evidence. Where no such evidence is supplied, we are without data; we are without first premises; and when, without these, we attempt to build up a science, we do as those who raise edifices without foundations. And what do such builders construct? Castles in the air.