It is exercise alone that supports the spirits, and keeps the mind in vigor.
In extraordinary events ignorance of their causes produces astonishment.
Friendship was given by nature to be an assistant to virtue, not a companion in vice.
Let every man practise the trade which he best understands.
But as to the affection which anyone may have for us, it is the first demand of duty that we do most for him who loves us most; but we should measure affection, not like youngsters, by the ardour of its passion, but rather by its strength and constancy.
To reduce man to the duties of his own city, and to disengage him from duties to the members of other cities, is to break the universal society of the human race.