Every art and every method, and in like manner every action and deliberate choice, appear to aspire after a certain good. Hence, it is well said, that the good is that which all things desire. Of ends, however, there appears to be a certain difference; for some of them are energies; but others of them besides these are certain works. But in those things in which there are certain ends besides the actions, in these the works are naturally adapted to be better than the energies. Since, however, there are many actions and arts, and sciences, there will also be many ends. For the end of medicine is health; of the ship-building art, a ship; of the military art, victory; and of the economic art, wealth. But such arts as are of this kind are [arranged] under one certain power; just as the bridle-making art is arranged under the equestrian art, and such other arts as pertain to equestrian instruments.