IX. But we must place those arguments first which make out the world to be uncreated and indestructible, because of our respect for that which is visible, employing an appropriate commencement. To all things which are liable to destruction there are two causes of that destruction, one being internal and the other external; therefore you may find iron, and brass, and all other substances of that kind destroyed by themselves when rust, like a creeping disease, overruns and devours them; and by external causes when, if a house or a city is burnt, they also are consumed in the conflagration, being melted by the violent impetuosity of the fire. A similar end also befalls animals, partly when they are sick of diseases arising internally, and partly when they are destroyed by external causes, being sacrificed, or stoned, or burnt, or when they endure an unclean death by hanging. And if the world also is destroyed, then it must of necessity be so either by some external cause, or else by some one of the powers which exist within itself; and both these alternatives are impossible, for there is nothing whatever outside of the world, since all things are brought together in order to make it complete and full, for it is in this way that it will be one, and whole, and free from old age; it will be one, because if anything were left outside of it, then another world might be created resembling that which exists now; and whole, because the whole of its essence is expended on itself; and exempt from old age and from all disease, since those bodies which are liable to be destroyed by disease or old age are violently overthrown by external causes, such as heat, and cold, and other contrary qualities, no power of which is able to escape so as to surround and attack the world, all those being entirely enclosed within, without any part whatever being separated from the rest. But if indeed there is any external thing it must by all means be a vacuum, or else a nature absolutely impossible, which it would be impossible should either suffer or do anything. And again, it will also not be dissolved by any cause existing within itself; first of all because, if it were, then the part would be greater and more powerful than the whole, which is the greatest possible absurdity, for the world, enjoying an unsurpassable power, influences all its parts, and is not itself influenced or moved by any one of them; in the second place because, since there are two causes of corruption, the one being internal and the other external, those things which are competent to admit the one must also by all means be liable to the other; 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.