On The Heavens   

and cannot at any future time be truly said not to be.) If, again, the

two terms are coincident, if the ungenerated is indestructible, and

the indestructible ungenearted, then each of them is coincident with

'eternal'; anything ungenerated is eternal and anything indestructible

is eternal. This is clear too from the definition of the terms,

Whatever is destructible must be generated; for it is either

ungenerated, or generated, but, if ungenerated, it is by hypothesis

indestructible. Whatever, further, is generated must be

destructible. For it is either destructible or indestructible, but, if

indestructible, it is by hypothesis ungenerated.

If, however, 'indestructible' and 'ungenerated' are not

coincident, there is no necessity that either the ungenerated or the

indestructible should be eternal. But they must be coincident, for the

following reasons. The terms 'generated' and 'destructible' are

coincident; this is obvious from our former remarks, since between

what always is and what always is not there is an intermediate which

is neither, and that intermediate is the generated and destructible.

For whatever is either of these is capable both of being and of not

being for a definite time: in either case, I mean, there is a

certain period of time during which the thing is and another during

which it is not. Anything therefore which is generated or destructible

must be intermediate. Now let A be that which always is and B that

which always is not, C the generated, and D the destructible. Then C

must be intermediate between A and B. For in their case there is no

time in the direction of either limit, in which either A is not or B

is. But for the generated there must be such a time either actually or

potentially, though not for A and B in either way. C then will be, and

also not be, for a limited length of time, and this is true also of D,

the destructible. Therefore each is both generated and destructible.

Therefore 'generated' and 'destructible' are coincident. Now let E

stand for the ungenerated, F for the generated, G for the

indestructible, and H for the destructible. As for F and H, it has