On The Heavens
being and of not being; but this has been shown to be impossible.
(4) Again, if the capacity is present prior to the activity, it will
be present for all time, even while the thing was as yet ungenerated
and non-existent, throughout the infinite time in which it was capable
of being generated. At that time, then, when it was not, at that
same time it had the capacity of being, both of being then and of
being thereafter, and therefore for an infinity of time.
It is clear also on other grounds that it is impossible that the
destructible should not at some time be destroyed. For otherwise it
will always be at once destructible and in actuality indestructible,
so that it will be at the same time capable of always existing and
of not always existing. Thus the destructible is at some time actually
destroyed. The generable, similarly, has been generated, for it is
capable of having been generated and thus also of not always existing.
We may also see in the following way how impossible it is either for
a thing which is generated to be thenceforward indestructible, or
for a thing which is ungenerated and has always hitherto existed to be
destroyed. Nothing that is by chance can be indestructible or
ungenerated, since the products of chance and fortune are opposed to
what is, or comes to be, always or usually, while anything which
exists for a time infinite either absolutely or in one direction, is
in existence either always or usually. That which is by chance,
then, is by nature such as to exist at one time and not at another.
But in things of that character the contradictory states proceed
from one and the same capacity, the matter of the thing being the
cause equally of its existence and of its non-existence. Hence
contradictories would be present together in actuality.
Further, it cannot truly be said of a thing now that it exists
last year, nor could it be said last year that it exists now. It is
therefore impossible for what once did not exist later to be
eternal. For in its later state it will possess the capacity of not
existing, only not of not existing at a time when it exists-since then