On The Heavens   

without changes of properties. But all natural bodies which change

their properties we see to be subject without exception to increase

and diminution. This is the case, for instance, with the bodies of

animals and their parts and with vegetable bodies, and similarly

also with those of the elements. And so, if the body which moves

with a circular motion cannot admit of increase or diminution, it is

reasonable to suppose that it is also unalterable.

The reasons why the primary body is eternal and not subject to

increase or diminution, but unaging and unalterable and unmodified,

will be clear from what has been said to any one who believes in our

assumptions. Our theory seems to confirm experience and to be

confirmed by it. For all men have some conception of the nature of the

gods, and all who believe in the existence of gods at all, whether

barbarian or Greek, agree in allotting the highest place to the deity,

surely because they suppose that immortal is linked with immortal

and regard any other supposition as inconceivable. If then there is,

as there certainly is, anything divine, what we have just said about

the primary bodily substance was well said. The mere evidence of the

senses is enough to convince us of this, at least with human

certainty. For in the whole range of time past, so far as our

inherited records reach, no change appears to have taken place

either in the whole scheme of the outermost heaven or in any of its

proper parts. The common name, too, which has been handed down from

our distant ancestors even to our own day, seems to show that they

conceived of it in the fashion which we have been expressing. The same

ideas, one must believe, recur in men's minds not once or twice but

again and again. And so, implying that the primary body is something

else beyond earth, fire, air, and water, they gave the highest place a

name of its own, aither, derived from the fact that it 'runs always'

for an eternity of time. Anaxagoras, however, scandalously misuses

this name, taking aither as equivalent to fire.

It is also clear from what has been said why the number of what we