In Book I, chapter 9, of On the Heavens Aristotle concludes that nothing, neither “place”, “void” nor “time”, lies outside the heaven. He speaks of what is beyond as “unalterable and unmodified”, and of the “duration” (aion) of the whole heaven, a word which he says “possessed a divine significance for the ancients”. The passage is the source of a famous derivation of the word, and it stands under this term for that reason.
Read in contextIt is clear then that there is neither place, nor void, nor time, outside the heaven. Hence whatever is there, is of such a nature as not to occupy any place, nor does time age it; nor is there any change in any of the things which lie beyond the outermost motion; they continue through their entire duration unalterable and unmodified, living the best and most selfsufficient of lives. As a matter of fact, this word ‘duration’ possessed a divine significance for the ancients, for the fulfilment which includes the period of life of any creature, outside of which no natural development can fall, has been called its duration. On the same principle the fulfilment of the whole heaven, the fulfilment which includes all time and infinity, is ‘duration’-a name based upon the fact that it is always-duration immortal and divine.
