In poverty and other misfortunes of life, true friends are a sure refuge.

The soul of animals is characterized by two faculties, (a) the faculty of discrimination which is the work of thought and sense, and (b) the faculty of originating local movement.

By 'life,' we mean a thing that can nourish itself and grow and decay.

All men by nature desire knowledge.

Everything necessarily is or is not, and will be or will not be; but one cannot divide and say that one or the other is necessary.I mean, for example: it is necessary for there to be or not to be a sea-battle tomorrow; but it is not necessary for a sea-battle to take place tomorrow, or for one not to take place--though it is necessary for one to take place or not to take place.

The body is most fully developed from thirty to thirty-five years of age, the mind at about forty-nine.

The things best to know are first principles and causes, but these things are perhaps the most difficult for men to grasp, for they are farthest removed from the senses.