To a review of the Platonic doctrine, Aristotle devotes a whole chapter. He urges against it various objections, very much of a piece with those brought against the theory of Ideas generally. If there be but one good, there should be but one science; the alleged Idea is merely a repetition of the phenomena; the recognized goods (_i.e._, varieties of good) cannot be brought under one Idea; moreover, even granting the reality of such an Idea, it is useless for all practical purposes. What our science seeks is Good, human and attainable (VI.). The Supreme End is what is not only chosen as an End, but is never chosen except as an End: not chosen both for itself and with a view to something ulterior. It must thus be--(1) An _end-in-itself_ pursued for its own sake; (2) it must farther be _self-sufficing_ leaving no outstanding wants--man's sociability being taken into account and gratified. Happiness is such an end; but we must state more clearly wherein happiness consists. This will appear, if we examine what is the work appropriate and peculiar to man. Every artist, the sculptor, carpenter, currier (so too the eye and the hand), has his own peculiar work: and good, to him, consists in his performing that work well. Man also has his appropriate and peculiar work: not merely living--for that he has in common with vegetables; nor the life of sensible perception--for that he has in common with other animals, horses, oxen, &c. There remains the life of man as a rational being: that is, as a being possessing reason along with other mental elements, which last are controllable or modifiable by reason. This last life is the peculiar work or province of man. For our purpose, we must consider man, not merely as possessing, but as actually exercising and putting in action, these mental capacities. Moreover, when we talk generally of the work or province of an artist, we always tacitly imply a complete and excellent artist in his own craft: and so likewise when we speak of the work of a man, we mean that work as performed by a complete and competent man. Since the work of man, therefore, consists in the active exercise of the mental capacities, conformably to reason, the supreme good of man will consist in performing this work with excellence or virtue. Herein he will obtain happiness, if we assume continuance throughout a full period of life: one day or a short time is not sufficient for happiness (VII.).