[Aquinas begins with two objections
to the claim whose truth he means to prove, namely, that God exists. He
thereafter proves that God exists by five separate arguments before returning
to and answering the objections.]
Objection 1. It seems that God does
not exist; because if one of two contraries be infinite, the other would be
altogether destroyed. But the word "God" means that He is infinite
goodness. If, therefore, God existed, there would be no evil discoverable; but
there is evil in the world. Therefore God does not exist.
Objection 2. Further, it is
superfluous to suppose that what can be accounted for by a few principles has
been produced by many. But it seems that everything we see in the world can be
accounted for by other principles, supposing God did not exist. For all natural
things can be reduced to one principle which is nature; and all voluntary
things can be reduced to one principle which is human reason, or will.
Therefore there is no need to suppose God's existence.
On the contrary, It is said in the
person of God: "I am Who am." (Exodus 3:14)
I answer that, The existence of God
can be proved in five ways.
The first and more manifest way is
the argument from motion. It is certain, and evident to our senses, that in the
world some things are in motion. Now whatever is in motion is put in motion by
another, for nothing can be in motion except it is in potentiality to that
towards which it is in motion; whereas a thing moves inasmuch as it is in act.
For motion is nothing else than the reduction of something from potentiality to
actuality. But nothing can be reduced from potentiality to actuality, except by
something in a state of actuality. Thus that which is actually hot, as fire,
makes wood, which is potentially hot, to be actually hot, and thereby moves and
changes it. Now it is not possible that the same thing should be at once in
actuality and potentiality in the same respect, but only in different respects.
For what is actually hot cannot simultaneously be potentially hot; but it is
simultaneously potentially cold. It is therefore impossible that in the same
respect and in the same way a thing should be both mover and moved, i.e. that
it should move itself. Therefore, whatever is in motion must be put in motion
by another. If that by which it is put in motion be itself put in motion, then
this also must needs be put in motion by another, and that by another again.
But this cannot go on to infinity, because then there would be no first mover,
and, consequently, no other mover; seeing that subsequent movers move only
inasmuch as they are put in motion by the first mover; as the staff moves only
because it is put in motion by the hand. Therefore it is necessary to arrive at
a first mover, put in motion by no other; and this everyone understands to be
God.
The second way is from the nature
of the efficient cause. In the world of sense we find there is an order of
efficient causes. There is no case known (neither is it, indeed, possible) in
which a thing is found to be the efficient cause of itself; for so it would be
prior to itself, which is impossible. Now in efficient causes it is not
possible to go on to infinity, because in all efficient causes following in
order, the first is the cause of the intermediate cause, and the intermediate
is the cause of the ultimate cause, whether the intermediate cause be several,
or only one. Now to take away the cause is to take away the effect. Therefore,
if there be no first cause among efficient causes, there will be no ultimate,
nor any intermediate cause. But if in efficient causes it is possible to go on
to infinity, there will be no first efficient cause, neither will there be an
ultimate effect, nor any intermediate efficient causes; all of which is plainly
false. Therefore it is necessary to admit a first efficient cause, to which
everyone gives the name of God.
The third way is taken from
possibility and necessity, and runs thus. We find in nature things that are
possible to be and not to be, since they are found to be generated, and to
corrupt, and consequently, they are possible to be and not to be. But it is
impossible for these always to exist, for that which is possible not to be at
some time is not. Therefore, if everything is possible not to be, then at one
time there could have been nothing in existence. Now if this were true, even
now there would be nothing in existence, because that which does not exist only
begins to exist by something already existing. Therefore, if at one time
nothing was in existence, it would have been impossible for anything to have
begun to exist; and thus even now nothing would be in existence — which is
absurd. Therefore, not all beings are merely possible, but there must exist
something the existence of which is necessary. But every necessary thing either
has its necessity caused by another, or not. Now it is impossible to go on to
infinity in necessary things which have their necessity caused by another, as
has been already proved in regard to efficient causes. Therefore we cannot but
postulate the existence of some being having of itself its own necessity, and
not receiving it from another, but rather causing in others their necessity.
This all men speak of as God.
The fourth way is taken from the
gradation to be found in things. Among beings there are some more and some less
good, true, noble and the like. But "more" and "less" are
predicated of different things, according as they resemble in their different
ways something which is the maximum, as a thing is said to be hotter according
as it more nearly resembles that which is hottest; so that there is something
which is truest, something best, something noblest and, consequently, something
which is uttermost being; for those things that are greatest in truth are
greatest in being, as it is written in Metaph. ii. Now the maximum in any genus
is the cause of all in that genus; as fire, which is the maximum heat, is the
cause of all hot things. Therefore there must also be something which is to all
beings the cause of their being, goodness, and every other perfection; and this
we call God.
The fifth way is taken from the
governance of the world. We see that things which lack intelligence, such as
natural bodies, act for an end, and this is evident from their acting always,
or nearly always, in the same way, so as to obtain the best result. Hence it is
plain that not fortuitously, but designedly, do they achieve their end. Now
whatever lacks intelligence cannot move towards an end, unless it be directed
by some being endowed with knowledge and intelligence; as the arrow is shot to
its mark by the archer. Therefore some intelligent being exists by whom all
natural things are directed to their end; and this being we call God.
Reply to Objection 1. As Augustine
says (Enchiridion xi): "Since God is the highest good, He would not allow
any evil to exist in His works, unless His omnipotence and goodness were such
as to bring good even out of evil." This is part of the infinite goodness
of God, that He should allow evil to exist, and out of it produce good.
Reply to Objection 2. Since nature
works for a determinate end under the direction of a higher agent, whatever is
done by nature must needs be traced back to God, as to its first cause. So also
whatever is done voluntarily must also be traced back to some higher cause
other than human reason or will, since these can change or fail; for all things
that are changeable and capable of defect must be traced back to an immovable
and self-necessary first principle, as was shown in the body of the Article.
