Summa
Thelogica
First Part: Sacred Doctrine
Does God
exist?
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. |