), the opinion of
philosophers who asserted the eternity of the world was twofold. For
some said that the substance of the world was not from God, which is
an intolerable error; and therefore it is refuted by proofs that are
cogent. Some, however, said that the world was eternal, although made
by God. For they hold that the world has a beginning, not of time,
but of creation, so that in a certain hardly intelligible way it was
always made. "And they try to explain their meaning thus (De Civ. Dei
x, 31): for as, if the foot were always in the dust from eternity,
there would always be a footprint which without doubt was caused by
him who trod on it, so also the world always was, because its Maker
always existed." To understand this we must consider that the
efficient cause, which acts by motion, of necessity precedes its
effect in time; because the effect is only in the end of the action,
and every agent must be the principle of action. But if the action is
instantaneous and not successive, it is not necessary for the maker
to be prior to the thing made in duration as appears in the case of
illumination. Hence they say that it does not follow necessarily if
God is the active cause of the world, that He should be prior to the
world in duration; because creation, by which He produced the world,
is not a successive change, as was said above (Q. 45, A. 2).

Reply Obj. 2: Those who would say that the world was eternal, would
say that the world was made by God from nothing, not that it was made
after nothing, according to what we understand by the word creation,
but that it was not made from anything; and so also some of them do
not reject the word creation, as appears from Avicenna (Metaph. ix,
text 4).

Reply Obj. 3: This is the argument of Anaxagoras (as quoted in Phys.
viii, text 15). But it does not lead to a necessary conclusion,
except as to that intellect which deliberates in order to find out
what should be done, which is like movement. Such is the human
intellect, but not the divine intellect (Q. 14, AA. 7, 12).

Reply Obj. 4: Those who hold the eternity of the world hold that
some region was changed an infinite number of times, from being
uninhabitable to being inhabitable and "vice versa," and likewise
they hold that the arts, by reason of various corruptions and
accidents, were subject to an infinite variety of advance and decay.
Hence Aristotle says (Meteor. i), that it is absurd from such
particular changes t