For life is an exercise of faculties, and each man exercises the faculties he most loves upon the things he most loves; e.g. the musical man exercises his hearing upon melodies, and the studious man exercises his intellect upon matters of speculation, and so on with the rest.

But pleasure completes the exercise of faculties, and therefore life, which men desire.

Naturally, therefore, men desire pleasure too; for each man finds in it the completion of his life, which is desirable.

But whether we desire life for the sake of pleasure, or pleasure for the sake of life, is a question which we may dismiss for the present. For the two seem to be joined together, and not to admit of separation: without exercise of faculties there is no pleasure, and every such exercise is completed by pleasure.