[23] and a proof of this may be found in oxen, and horses, and men, and other animals of similar kinds, because it is their nature to be destroyed by the sword, or to be liable to die by disease; for it is difficult, or I might rather say impossible, to find anything which, being by nature at the mercy of some external cause perceptible by the intellect, will still not be liable to corruption... by itself when the world was not.