en of another in an infinite
series. But the father is the efficient cause of the son (Phys. ii,
text 5). Therefore in efficient causes there could be an infinite
series, which is disproved (Metaph. ii, text 5).

Obj. 8: Further, if the world and generation always were, there have
been an infinite number of men. But man's soul is immortal: therefore
an infinite number of human souls would actually now exist, which is
impossible. Therefore it can be known with certainty that the world
began, and not only is it known by faith.

_On the contrary,_ The articles of faith cannot be proved
demonstratively, because faith is of things "that appear not" (Heb.
11:1). But that God is the Creator of the world: hence that the world
began, is an article of faith; for we say, "I believe in one God,"
etc. And again, Gregory says (Hom. i in Ezech.), that Moses
prophesied of the past, saying, "In the beginning God created heaven
and earth": in which words the newness of the world is stated.
Therefore the newness of the world is known only by revelation; and
therefore it cannot be proved demonstratively.

_I answer that,_ By faith alone do we hold, and by no demonstration
can it be proved, that the world did not always exist, as was said
above of the mystery of the Trinity (Q. 32, A. 1). The reason of this
is that the newness of the world cannot be demonstrated on the part
of the world itself. For the principle of demonstration is the
essence of a thing. Now everything according to its species is
abstracted from "here" and "now"; whence it is said that universals
are everywhere and always. Hence it cannot be demonstrated that man,
or heaven, or a stone were not always. Likewise neither can it be
demonstrated on the part of the efficient cause, which acts by will.
For the will of God cannot be investigated by reason, except as
regards those things which God must will of necessity; and what He
wills about creatures is not among these, as was said above (Q. 19,
A. 3). But the divine will can be manifested by revelation, on which
faith rests. Hence that the world began to exist is an object of
faith, but not of demonstration or science. And it is useful to
consider this, lest anyone, presuming to demonstrate what is of
faith, should bring forward reasons that are not cogent, so as to
give occasion to unbelievers to laugh, thinking that on such grounds
we believe things that are of faith.

Reply Obj. 1: As Augustine says (De Civ. Dei xi, 4