Controversy, though always an evil in itself, is sometimes a necessary evil.

As an exercise of the reasoning faculties, pure mathematics is an admirable exercise, because it consists of reasoning alone and does not encumber the student with any exercise of judgment.

Everyone wishes to have truth on his side, but not everyone wishes to be on the side of truth.

To know your ruling passion, examine your castles in the air.

To teach one who has no curiosity to learn, is to sow a field without ploughing it.

Falsehood, like the dry-rot, flourishes the more in proportion as air and light are excluded.

To follow imperfect, uncertain, or corrupted traditions, in order to avoid erring in our own judgment, is but to exchange one danger for another.