St. Thomas Aquinas
The Existence and Nature of God
Thomas Aquinas
Born in Roccasecca, Kingdom of Sicily, in 1224 or 25 and died at Fossanova, en route to
the Council of Lyons in 1274. A theologian and professor of Sacred Scripture at the
University of Paris, Thomas integrated the thought of Aristotle with Christian theology.
Summa Theologiae
Belief in God
Everyone believes in God. The only question is who or what God is.
Traditionally and historically
What a god is
A god is a superior, generally immortal kind of being, superior to human beings and
exercising some sort of governance over a part of the natural order. As understood by
Judaism, Christianity, and Islam, God is the Supreme Being and Creator of all things.
Human beings are ultimately responsible to him for their lives.
Believing in God
Every people of every age has worshipped God or gods. Religion and belief in something
divine are ubiquitous. Atheism is not ‘natural,’ not the ‘default’ position of the human mind
and heart.
Mikhail Gorbachev said: “Well, I believe in the cosmos. All of us are linked
to the cosmos. Look at the sun. If there is no sun, then we cannot exist. So
nature is my god. To me, nature is sacred. Trees are my temples and forests
are my cathedrals.”
The contemporary discussion.
Privatization of religion
Belief in God is a personal thing, one’s own business. So the existence of God is a religious
idea, but not an objective fact. Whether God is real and what God is cannot be known.
Each person has to decide who God is for him or herself.
Intellectual disrepute
The intellectual’s stance: “orthodox agnosticism.” Laplace on God’s role in the scientific
view of the universe: “Je n’ai pas besoin de cette hypothèse.” General hostility towards
God’s inclusion in science and human affairs
In sum:
To believe in God is today considered a decision of the will and not legitimately the fruit of
exercise of reason. So the question we ask ourselves is: ‘Is it reasonable to believe in God?’
Are there solid reasons for believing in God? Are there evidence and a chain of valid or
plausible argumentation establishing that God exists?
Summa Theologiae, q. 2: The existence of God
Article 1: The alleged self-evidence of God’s existence
Thomas first addresses himself to the devout belief that God is so great that no one could
miss him. Isn’t this the point I made above…that everyone believes in God anyway? So it’s
self-evident that God exists…right?
Objection 1: Teaching of one of the Church Fathers
Note the natural appeal of Damascene’s opinion, especially for a believer. We’re made in
God’s image; of course the knowledge of him is implanted in us.
Objection 2: St. Anselm’s famous «Ontological Argument»
Logical legerdemain or metaphysical insight? The issue: God is so great that he cannot
even be thought not to exist.
Objection 3: Self evidence of truth
If Jesus is the truth, then anyone who knows truth knows something of God, right?
Sed Contra and Response: Self-evidence & the meanings of terms.
Self evidence is a logical and conceptual notion, having to do with meanings of terms. “No
bachelor has a mother-in-law” is self evident. Thomas Jefferson’s self-evident truths are
not so for Aquinas. God’s existence is not and cannot be self-evident to us because we
cannot know the divine essence.
Digression on ‘essence’ and other Aristotelian concepts
Essence: “what a thing is”
When we know a thing’s essence, we have scientific knowledge of it. The essence is the
basis of a thing’s definition. Also important are

Matter: What that kind of thing is characteristically made of, and

Form: What kind or class of being it is.

Efficient cause: what made this thing to come into being.

Final cause: the good at which the thing aims; its purpose or goal; its perfection.
Potency and act
Complementary opposites: Potency is potentiality, power or capacity to become something
fully actual. Act is actuality, the realization of potentiality.
Does God exist? Article three
One of the most famous texts in philosophy and theology: St. Thomas Aquinas’s “Five
Ways” to prove the existence of God. (For a very detailed version of the first argument, see
Aquinas’s Summa Contra Gentiles, Volume 1. You can also check out Aristotle’s Physics,
where these arguments first appeared.)
Thomas’s strategy

We cannot know God directly. All we can know are his works.

If we look at his works (effects) we can know something about the maker that
produced them.

Therefore we can argue for God’s existence on the basis of things around us.
The “Five Ways”
1. From motion: There must be an unmoved First Mover.
2. From efficient causes: There must be an uncaused First Cause.
3. From possibility & necessity: There must be a first Necessary Being.
4. From the gradation of things: There must be highest, best thing that
causes all other goodness and perfection.
5. From governance of the world: There must be an intelligent being that
directs everything to its goal.
First Way – Change
This argument (as well as the 2nd one) is drawn from Aristotle.

Change is a fact of experience.

But nothing changes without something else changing it. Nothing that has a
potentiality makes that potentiality actual on its own.

Everything that changes requires something that changes it.

Whatever changes a thing must be changed by yet something else.

This something else must also be changed.

This cannot go on to an infinity of causes of change. Without some first cause,
nothing else would change.

Therefore there must be a First cause of change that is not itself changed. “This is
what everyone understands by God.”
Second Way
This is perhaps the most common popular argument. “How did the universe get here?”
There must be a God who made it.

In the observable world, causes come in series. We cannot find anything that causes
itself.

But a series of causes can’t go on forever, for there would be no first cause and
therefore no intermediate causes.
o Eliminate a cause and you eliminate its effects.

“So we are forced to postulate some first agent cause, to which everyone gives the
name God.”
Third Way
To our modern ears a strange argument, the Third Way actually addresses important
principles underlying the sciences and our understanding of the universe.

Some things are possible to be or not to be, since they are generated and corrupted.
They are made and destroyed.

Were such ‘possible’ beings the only beings, then it would be impossible for the
universe and what’s in it even to be. Beyond the ‘things’ in the universe are the
necessary laws and principles by which things are governed.

But the necessary laws and principles governing the universe must have an origin, a
cause. They are not ‘just there’, unexplained regularities.

Therefore there has to be a necessary Being from whom all other necessary beings
receive their necessity.
Fourth Way
This is drawn from the Platonic tradition.

Some things are more or less good, noble, beautiful, true, etc. than others.

But “more” and “less” are said according to some absolute standard. (This is how
Plato argued for his Forms.)

So there must be something that is cause of the perfection in all other things and
which is itself truest, noblest, best, and perfect in its being.

“This is what we call God.”
Fifth Way
This argument is finding echoes today in the “intelligent design” school in biology.

We see that inanimate objects act for a purpose. This is clear from the fact that they
obey what we call natural laws.

Hence, it is clear that their behavior is planned intelligently, just as an arrow is
aimed by the archer.

So, some intelligent being directs all things to their purpose, and this is God.
“And this is what everyone calls God”
This is the key to understanding these proofs. Everyone (almost) believes in a god of some
sort. Whatever is to count as God—supreme over all other beings, all-powerful, all-wise,
ultimate judge of good and evil—has to fit the criteria, as it were, in these proofs.
What to make of these proofs
Since they appeared, they have been subject of immense discussion and debate.
In a way, they present a philosophical version of what ordinary people think, when they
decide that there ‘has to be a God’ behind the world they live in.
Their logical ‘bite’
Of course, you can refuse to accept them, but the price is to consign the universe to
meaninglessness. There is no sense to anything and therefore no science and no ethical
standard of good.
Science does not affect their validity
Modern and contemporary sciences neither refute nor support Aquinas’s Five Ways. These
are not alternatives to physics. The Big Bang is not what Aquinas means by “first unmoved
mover.”
What they leave us with
Clearly, the Entity whose existence is proved by Aquinas’s Five Ways does not look a lot
like the God we worship in church. In fact, there is precious little that we can say positively
about this being. We can, however, say a lot about what God is not.
They do show—and for us in the 21st Century this is most especially important—that belief
in God’s existence is not simply a matter of blind faith or subjective religious, moral, or
aesthetic inclination.