Proving that God Exists
St. Anselm & St. Thomas Aquinas
Can we prove God exists?
On one hand…
 People have believed in a God or gods for eons, and very few believers have been
philosophers or have studied philosophy.

Believing in God seems to have more to do with faith, with a life-commitment than
with proving something.
On the other…
 Pagan philosophers, such as Plato & Aristotle, argued that a supreme being must
exist.

The Bible says that “the heavens proclaim the glory of God.” (Ps. 19, 1), and the
Koran rebukes those who don’t recognize Allah’s many signs. For that matter, so
does St. Paul in Romans 1.
St. Anselm of Canterbury: The Ontological Argument

Although he was himself a very religious man, Anselm was also impressed by the power of
the human mind to use rational arguments to get to the truth of things. If the power of
reason is so great, then surely it must be able to prove that God exists. Eventually he came
up with his own ingenious argument

Anselm’s argument
God is a being than which nothing greater can be conceived (thought).

“The fool says in his heart, ‘There is no God.’” (Ps. 15, 1)

The Fool understands this, and what he understands is in his understanding.

It is one thing for an object to be in the understanding and another to understand it exists.

The Fool believes this, at least: that a being than which nothing greater can be conceived
exists in his understanding, for whatever is understood exists in the understanding.

However, this cannot exist in the understanding alone. If it did, it could be thought also to
exist in reality.

But to understand in reality would be greater.
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
Clinching the argument
If this being – one than which nothing greater can be thought – exists in the understanding alone,
we can think of a greater one … namely, such a being existing in reality.

“Hence there is no doubt that there exists a being than which nothing greater can be conceived, and
[that] it exists both in the understanding and in reality.”
Therefore, God exists.

A 2nd version
We can think of a being which cannot be thought not to exist. This is greater than one that
could be thought not to exist.

So, if this being – than which nothing greater can be thought – can be thought not to exist, then a
greater being can be conceived.

But that is an irreconcilable contradiction. Therefore, this being does exists and cannot
even be thought not to exist.
The idea here is that God is so great that it is impossible to think of him as not existing.
Where the Fool went wrong
If Anselm is right, then how could the Fool even say this, that there is no God? Aristotle says
that we cannot think a contradiction—not really. One 20th Century philosopher has even said
that Anselm proves that God does not exist. Why? Because if God is a being whose nonexistence is inconceivable, he must not exist, because there are many people who do deny his
existence.
Anselm answers by distinguishing two ways of ‘conceiving’ (‘thinking’) something:
When the word alone is though.
So according to the words, we can think that fire is water.
When the very entity conceived is understood.
Anyone who knows fire cannot think this, for it is contrary to the nature of fire to be water.
So no one who understands what God is can think that he does not exist.
That is to say, the Fool is just saying the words.
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Therefore…
God exists supremely, as the being than which nothing greater can be thought. Therefore he
must be the highest of beings, Creator of all, and lacking no good.
“You [God] are just, truthful, blessed, and whatever it is better to be than not to be.”
Reply: On behalf of the Fool by Gaunilo, the Monk

“Not so!” says Gaunilo.
Granted, this being than which nothing greater can be thought is in the understanding. We
still cannot conclude that it has to exist. Anselm has to pay stricter attention to what he is
saying.

This being has no real existence in my mind when I think it. You have to prove it exists
first, before you say it exists in the mind.
For example: The Lost Island
Gaunilo describes a fabulous island of immense wealth and delicacies. If you say this island
exists, Gaunilo understands you. But suppose you deny it. Can one not argue that since it
exists in your imagination, it must exist in reality, because a really existing island is much better
than a merely imaginary one.
“Well,” says Gaunilo, “that’s what Anselm has done with God.”
Anselm’s Response
The case with God is different. When we conceive God as a Being than which nothing greater can be
thought, we think of him as he really is and not just of a collection of words. The Lost Island
example does not really apply.
Where this argument comes from
In one way, it’s from the Bible: God said to Moses, “I am Who am.” (Exodus 3, 14) God is his
own existence. In another way, Plato and his disciples suggest it. According Plato’s theory of
Forms, every perfection has its supreme perfection. So there is a highest degree of being and
this is God. The Christian, Jewish, and Moslem philosophers said that degree of being must
belong to God.
And it seems right to say that God exists so perfectly that he cannot not exist. Otherwise he
would be less than supreme.
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