In the first place, courage has protected the fierce brood of lions, and the savage races of other wild animals; and craft has secured the fox, as swiftness has saved the stag. But the light-slumbering breed of dogs, with their faithful affections, and all the various species of horses, and the woolly flocks, too, and horned cattle, all these, my dear Memmius, are committed to the protection of man. For they have anxiously avoided wild beasts, and have sought peace; and plenty of subsistence has been provided for them without labour of theirs, which subsistence we secure to them as a reward in return for their service. But of those to whom nature has given no such qualities, that they should either be able to live of themselves, or to afford us any service, why should we suffer the races to be maintained and protected by our support? Indeed all these, rendered helpless by their own fatal bonds, were exposed as a prey and a prize to other animals, until nature brought their whole species to destruction.

But Centaurs, and such creatures, there neither were, nor ever can be; for there can never exist an animal formed of a double nature and of two bodies; an animal made up of such heterogeneous members that the power in the opposite portions of the frame cannot possibly be equal. This you may learn, with however dull an understanding, from the following observations.

First, the horse, when three years of his age have passed, is flourishing in full vigour; the boy, at this time of life, is by no means so, but will even often seek in his sleep the milky teats of his mother’s breast. Afterwards, when, in old age, his lusty vigour and stout limbs are failing the horse, (growing torpid as life is departing,) behold, at that very period, the young man’s age being in its flower, youth prevails in him, and clothes his cheeks with soft down; so that you cannot possibly imagine that Centaurs can be composed or consist of a man and the servile seed of a horse; or that there can be Scyllae, of half-marine bodies, cinctured with fierce dogs; or other monsters of this sort, whose parts we observe to be incompatible with each other; parts which neither grow up together in their bodies, nor acquire vigour together, nor lose their strength together in old age; and which are neither excited by the same objects of affection, nor agree with the same tempers, nor find that the same kinds of food are nutritious to their bodies. For you may observe that bearded goats often grow fat on hemlock, which to men is rank poison.