QUESTION 2: THE EXISTENCE OF GOD
Because the chief aim of sacred doctrine is to teach the knowledge of
God, not only as He is in Himself, but also as He is the beginning of
things and their last end, and especially of rational creatures, as is
clear from what has been already said, therefore, in our endeavor to
expound this science, we shall treat: (1) Of God; (2) Of the rational
creature's advance towards God; (3) Of Christ, Who as man, is our way to
In treating of God there will be a threefold division, for we shall
consider: (1) Whatever concerns the Divine Essence; (2) Whatever concerns
the distinctions of Persons; (3) Whatever concerns the procession of
creatures from Him.
Concerning the Divine Essence, we must consider: (1) Whether God exists?
(2) The manner of His existence, or, rather, what is NOT the manner of
His existence; (3) Whatever concerns His operations---namely, His
knowledge, will, power.
Concerning the first, there are three points of inquiry:
(1) Whether the proposition "God exists" is self-evident?
(2) Whether it is demonstrable?
(3) Whether God exists?
Article 1: Whether the existence of God is self-evident?
Objection 1: It seems that the existence of God is self-evident. Now those
things are said to be self-evident to us the knowledge of which is
naturally implanted in us, as we can see in regard to first principles.
But as Damascene says (De Fide Orth. i, 1,3), "the knowledge of God is
naturally implanted in all." Therefore the existence of God is
Objection 2: Further, those things are said to be self-evident which are known as soon as the terms are known, which the Philosopher (1 Poster. iii) says is true of the first principles of demonstration. Thus, when the nature of a whole and of a part is known, it is at once recognized that every whole is greater than its part. But as soon as the signification of the word "God" is understood, it is at once seen that God exists. For by this word is signified that thing than which nothing greater can be conceived. But that which exists actually and mentally is greater than that which exists only mentally. Therefore, since as soon as the word "God" is understood it exists mentally, it also follows that it exists actually. Therefore the proposition "God exists" is self-evident.
Objection 3: Further, the existence of truth is self-evident. For whoever
denies the existence of truth grants that truth does not exist: and, if
truth does not exist, then the proposition "Truth does not exist" is
true: and if there is anything true, there must be truth. But God is
truth itself: "I am the way, the truth, and the life" (Jn. 14:6)
Therefore "God exists" is self-evident.
On the contrary, No one can mentally admit the opposite of what is
self-evident; as the Philosopher (Metaph. iv, lect. vi) states concerning
the first principles of demonstration. But the opposite of the
proposition "God is" can be mentally admitted: "The fool said in his
heart, There is no God" (Ps. 52:1). Therefore, that God exists is not
I answer that, A thing can be self-evident in either of two ways: on the
one hand, self-evident in itself, though not to us; on the other,
self-evident in itself, and to us. A proposition is self-evident because
the predicate is included in the essence of the subject, as "Man is an
animal," for animal is contained in the essence of man. If, therefore the
essence of the predicate and subject be known to all, the proposition
will be self-evident to all; as is clear with regard to the first
principles of demonstration, the terms of which are common things that no
one is ignorant of, such as being and non-being, whole and part, and such
like. If, however, there are some to whom the essence of the predicate
and subject is unknown, the proposition will be self-evident in itself,
but not to those who do not know the meaning of the predicate and subject
of the proposition. Therefore, it happens, as Boethius says (Hebdom., the
title of which is: "Whether all that is, is good"), "that there are some
mental concepts self-evident only to the learned, as that incorporeal
substances are not in space." Therefore I say that this proposition, "God
exists," of itself is self-evident, for the predicate is the same as the
subject, because God is His own existence as will be hereafter shown
(Question , Article ). Now because we do not know the essence of God, the
proposition is not self-evident to us; but needs to be demonstrated by
things that are more known to us, though less known in their
nature---namely, by effects.
Reply to Objection 1: To know that God exists in a general and confused way is
implanted in us by nature, inasmuch as God is man's beatitude. For man
naturally desires happiness, and what is naturally desired by man must be
naturally known to him. This, however, is not to know absolutely that God
exists; just as to know that someone is approaching is not the same as to
know that Peter is approaching, even though it is Peter who is
approaching; for many there are who imagine that man's perfect good which
is happiness, consists in riches, and others in pleasures, and others in
Reply to Objection 2: Perhaps not everyone who hears this word "God" understands
it to signify something than which nothing greater can be thought, seeing
that some have believed God to be a body. Yet, granted that everyone
understands that by this word "God" is signified something than which
nothing greater can be thought, nevertheless, it does not therefore
follow that he understands that what the word signifies exists actually,
but only that it exists mentally. Nor can it be argued that it actually
exists, unless it be admitted that there actually exists something than
which nothing greater can be thought; and this precisely is not admitted
by those who hold that God does not exist.
Reply to Objection 3: The existence of truth in general is self-evident but the
existence of a Primal Truth is not self-evident to us.
Article 2: Whether it can be demonstrated that God exists?
Objection 1: It seems that the existence of God cannot be demonstrated. For it
is an article of faith that God exists. But what is of faith cannot be
demonstrated, because a demonstration produces scientific knowledge;
whereas faith is of the unseen (Heb. 11:1). Therefore it cannot be
demonstrated that God exists.
Objection 2: Further, the essence is the middle term of demonstration. But we
cannot know in what God's essence consists, but solely in what it does
not consist; as Damascene says (De Fide Orth. i, 4). Therefore we cannot
demonstrate that God exists.
Objection 3: Further, if the existence of God were demonstrated, this could
only be from His effects. But His effects are not proportionate to Him,
since He is infinite and His effects are finite; and between the finite
and infinite there is no proportion. Therefore, since a cause cannot be
demonstrated by an effect not proportionate to it, it seems that the
existence of God cannot be demonstrated.
On the contrary, The Apostle says: "The invisible things of Him are
clearly seen, being understood by the things that are made" (Rm. 1:20).
But this would not be unless the existence of God could be demonstrated
through the things that are made; for the first thing we must know of
anything is whether it exists.
I answer that, Demonstration can be made in two ways: One is through the
cause, and is called "a priori," and this is to argue from what is prior
absolutely. The other is through the effect, and is called a
demonstration "a posteriori"; this is to argue from what is prior
relatively only to us. When an effect is better known to us than its
cause, from the effect we proceed to the knowledge of the cause. And from
every effect the existence of its proper cause can be demonstrated, so
long as its effects are better known to us; because since every effect
depends upon its cause, if the effect exists, the cause must pre-exist.
Hence the existence of God, in so far as it is not self-evident to us,
can be demonstrated from those of His effects which are known to us.
Reply to Objection 1: The existence of God and other like truths about God,
which can be known by natural reason, are not articles of faith, but are
preambles to the articles; for faith presupposes natural knowledge, even
as grace presupposes nature, and perfection supposes something that can
be perfected. Nevertheless, there is nothing to prevent a man, who cannot
grasp a proof, accepting, as a matter of faith, something which in itself
is capable of being scientifically known and demonstrated.
Reply to Objection 2: When the existence of a cause is demonstrated from an
effect, this effect takes the place of the definition of the cause in
proof of the cause's existence. This is especially the case in regard to
God, because, in order to prove the existence of anything, it is
necessary to accept as a middle term the meaning of the word, and not its
essence, for the question of its essence follows on the question of its
existence. Now the names given to God are derived from His effects;
consequently, in demonstrating the existence of God from His effects, we
may take for the middle term the meaning of the word "God".
Reply to Objection 3: From effects not proportionate to the cause no perfect
knowledge of that cause can be obtained. Yet from every effect the
existence of the cause can be clearly demonstrated, and so we can
demonstrate the existence of God from His effects; though from them we
cannot perfectly know God as He is in His essence.
Article 3: Whether God exists?
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." (Ex. 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
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