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.
Obj. 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.
Obj. 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" (Rom.
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 Obj. 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 Obj. 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 Obj. 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.
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