In every uncertain and important business it is proper to invoke God, because he is the good Creator of the world, and because nothing is uncertain with him who is possessed of the most accurate knowledge of all things. But of all times it is most necessary to invoke him when one is preparing to discuss the incorruptibility of the world; for neither among the things which are visible to the outward senses is there anything more admirably complete than the world, nor among things appreciable by the intellect is there anything more perfect than God. But the mind is at all times the governor of the outward sense, and that which is appreciable by the intellect is at all times superior to that which is visible to the outward senses, but those persons in whom there is implanted a vigorous and earnest love of truth willingly undergo the trouble of making inquiries relative to the subordinate things, from that which is superior to and the ruler over them.
 If then, we, who have been practised and trained in all the doctrines of prudence, and temperance, and virtue, have discarded all the stains of the passions and diseases, perhaps God would not disdain to give to souls completely purified and cleansed, so as to appear in his image, a knowledge of heavenly things either by means of dreams, or of oracles, or of signs, or of wonders. But since we have on us the marks of folly, and injustice, and of all other vices strongly stamped upon us and difficult to be effaced, we must be content even if we are only able by them to discover some faint copy and imitation of the truth. It is right, therefore, for those who are investigating the question whether the world is perishable, since the two words, "corruption," and "the world," will be in continual use, first of all to investigate the precise meaning of both expressions, in order that we may know what is now signified, and what has been ordained. And we must enumerate, not indeed everything which is signified by those words, but so much as is useful for the purpose of our present instruction.
 The world, therefore, is spoken of in its primary sense
 
as a single system, consisting of the heaven and the stars in the circumference of the earth, and all the animals and plants which are upon it; and in another sense it is spoken of merely as the heaven. And Anaxagoras, having a regard to this fact, once made answer to a certain person who asked of him what the reason was why he generally endeavoured to pass the night in the open air, that he did so for the sake of beholding the world, by which expression he meant the motions and revolutions of the stars.
And in its third meaning, as the Stoics affirm, it is a certain admirably-arranged essence, extending to the period of conflagration, either beautifully adorned or unadorned, the periods of the motion of which are called time.
But at present the subject of our consideration is the world, taken in the first sense of the word, which being one only, consists of the heaven, and of the earth, and of all that is therein. And the term corruption is used to signify a change for the worse; it is also used to signify the utter destruction of that which exists, a destruction so complete as to have no existence at all; for as nothing is generated out of nothing, so neither can anything which exists be destroyed so as to become non-existence. This is similar to Lucretius’s doctrine- Nil igitur fieri de nihilo posse putandum est. For it is impossible that anything should be generated of that which has no existence anywhere, as equally so that what does exist should be so utterly destroyed as never to be mentioned or heard of again. And indeed in this spirit the tragedian says:— "Nought that e’er has been Completely dies, but things combined Before another union find; Quitting their former company, And so again in other forms are seen." From the Chrysippus of Euripides.