The Cosmological Argument
Classic Philosophical Questions Part 3 - Philosophy of Religion
St. Thomas Aquinas, from The Basic Writings of St. Thomas Aquinas
Kem Stone - 19 August 2007
After looking at an argument that tries (and fails quite conclusively in my opinion) to establish proof of the
existence of God based on a priori principles, the text presents us with a different sort of argument for God’s
existence, an argument based on observable facts or empirical evidence. This is the cosmological argument for
the existence of God, and St. Thomas Aquinas formulates five different variations of it, all of which are based on
evidence and sound logic, but none of which are immune to doubt.
Aquinas begins by addressing three objections that may be offered by those who believe the cosmological
argument is unnecessary because the existence of God is self-evident, and we need only look to a priori
principles to understand the necessity of God’s existence. Before answering these objections, he distinguishes
between two different ways in which a thing may be self-evident: “on the one hand, self-evident in itself, though
not to us; on the other, self-evident in itself, and to us” (73). If the predicate of a proposition is included in the
essence of the subject (e.g. Man is an animal) the proposition is self-evident in the former sense (we all
understand that animal is contained in the essence of man). But if there are some to whom the essence of the
predicate and subject are not known, the proposition may only be self-evident in the latter sense, and its truth will
have to demonstrated by things that are understood. So although the existence of God may be self-evident,
because the essence of God is unknown, the cosmological argument is required to establish His existence.
The first objection Aquinas presents is that knowledge of the existence of God exists naturally within us, to which
he replies that this knowledge may in fact exist in us naturally, but only in a general way. “For man naturally
desires happiness, and what is naturally desired by man is naturally known by him” (73). So man is aware of the
existence of a perfect good (because it is what he most deeply desires) but in the same way that “to know
someone is approaching is not the same as to know that Peter is approaching” (73), we do not have inherent
knowledge that this perfect good is God.
The second objection is that God’s existence can be established by the ontological argument: that as soon as it is
understood that God is a being than which nothing greater can be conceived, we understand that by this very
nature God must exist, as it is greater to exist in reality than in the understanding alone. Aquinas refutes the
argument by pointing out that not everyone understands the essence of God as a being than which nothing greater
can be conceived. He also offers a variation of the objection which I have given to the ontological argument: “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” (73).
The final objection is that the existence of God is self-evident because the existence of truth is self-evident, and
according to the Bible, God is truth. “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” (72). As logically sound as the argument for the existence of truth is, Aquinas points out that there
is a confusion here between the existence of truth in general, such as the truth of a proposition, and the existence
of a Primal Truth, or fundamental reality, which is not self-evident.
Aquinas then turns to the critical question of whether God exists. He presents two commonly offered objections
to the existence of God, and after presenting his five variations of the cosmological argument, he refutes them
briefly. First is the problem of evil: that if God means infinite goodness, and God really existed, there would be no
evil. Aquinas does not give this argument a fraction of the treatment that it really warrants (as it is a very strong
objection), merely re-stating St. Augustine’s claim that allowing evil to exist and bringing good out of it is part of
God’s infinite goodness. Secondly, many contend that to suppose God’s existence is unnecessary, as the
existence of such a being is not needed to account for all that exists in the world. All natural things can be reduced
to the principle of nature, and all voluntary things can be reduced to human reason or will. Aquinas brushes over
this objection as well, merely re-stating his own fifth variation of the cosmological argument: “Since nature works
for a determinate end under the direction of a higher agent, whatever is done by nature must be traced back to
God as to its first cause” (75). Simply put, though all natural phenomena can be explained according to natural
law, natural law itself requires God as an explanation.
It is this form of logic which forms the basis of each of the five ways in which Aquinas asserts the existence of God
can be proven. He presents us with evidence from our experience of the world that requires an ultimate
explanation. Each argument establishes the necessity for the existence of a being which could serve as the ultimate
explanation, namely a prime mover, a first cause, a necessary being, a perfect good, and an intelligent being which
directs all natural things. In each case, Aquinas asserts that this role can only be filled by God.
His first argument is that which he derives from motion. It is evident to our senses, he asserts, that certain things in
the world are in motion. We know that that for anything to be in motion, it must be moved by something else, “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” (74). For instance, if wood is cold it is
potentially hot, but if fire burns the wood it becomes actually hot, and is no longer potentially hot but potentially
cold. A thing cannot be simultaneously potentially hot and actually hot, just as a thing cannot be both mover and
moved. Therefore anything in motion must have been moved by another, and because this cannot go on ad
infinitum, there must have been a first mover, and this is God.
His second argument is from the nature of efficient cause, and it is nearly identical to the first. In the world of our
senses we find an order of efficient causes. In the same way that a thing cannot be moved by itself, a thing cannot
be caused by itself. So everything requires an external cause, but this chain of causes can not go on to infinity
because there would then be no ultimate cause, and thus no effects. But we see effects taking place constantly,
and therefore there must have been a first cause, which could only be God.
The third argument is also very similar but perhaps the strongest formulation of them all, as Aquinas states the case
in terms of possibility and necessity. He states the evidence thusly: “We find in nature things that are possible to
be and not to be, since they are found to be generated, and to be corrupted, and consequently, it is possible for
them to be and not to be” (75). These beings have contingent existence, and are to be distinguished from beings
which have necessary existence which are not generated and cannot be corrupted. A necessary being exists
because it is impossible for such a being not to exist. One of the most solid metaphysical claims I have ever come
across is stated here: “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” (75). It would appear that to
assert that all beings are contingent is an absurdity, and therefore there must be at least one necessary being upon
which all other beings are contingent, and this being must be God.
The final two arguments are much weaker, and formulated somewhat differently though still in the same basic
spirit. “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”
(75). Aquinas insists that due to this gradation of qualities we find in nature, there must always be a maximum to
which that gradation approaches. Things are more or less x according as they resemble their maximum, while the
maximum x is the cause of anything else which is x. Simply substitute goodness for x and we find the need for
some perfect good which is the cause of all goodness, and this of course is God.
The last and by far the weakest argument is taken from the governance of the world. Aquinas points to the
evidence we see that things which lack knowledge such as natural bodies, act for an end which is nearly always to
obtain the best result. He asserts that nothing which moves toward an end could do so unless directed by some
intelligence—it cannot achieve its end merely by chance or fortune. “Therefore some intelligent being exists by
whom all natural things are directed to their end: and this being we call God” (75).
My objection to the fifth argument is simply to reject the entire claim. I do not believe it evident that beings which
lack knowledge act towards an end, and they most certainly do not act always as to produce the best result. An
asteroid floating in space is directed by the gravitational forces of the sun and planets, and should it collide with
Earth it could absolutely not be asserted that it has acted to obtain the “best result” and I cannot imagine what
Aquinas has in mind when he uses the term “best result” here anyway. How is he to know what the “best result”
of the action of a knowledge-lacking being might be? It is clear we do not need an intelligent being to explain the
actions of non-sentient beings—we can appeal to natural laws—so this argument fails completely. However, it
may be that we need such a being to explain the existence of these natural laws, though I believe this falls under
the much stronger second argument, that which asserts the need for a first cause.
The fourth argument is flawed as well for precisely the same reason that the ontological argument is flawed. To
assert that a thing is good insofar as it approaches the maximum of goodness is an error, and reminds me of the
“third man” fallacy in Plato’s theory of forms. We can use the analogy of heat to recognise the absurdity—is
something hot insofar as it approaches the maximum of heat? But we know that there is no such thing as a
maximum level of heat (there is no highest possible temperature), so why should we not also refuse to admit that
there is no such thing as a maximum level of goodness? If I conceive of the greatest good, can I not then conceive
that there is something of an even greater good than this, and so on?
I will take the first three arguments as one, because they are all very similar and I believe they are all very strong.
In fact, I believe they are the strongest arguments that have ever been presented for the necessity of God’s
existence. There are certain things about existence which seem to require God as an explanation, and among
these are motion, the order of efficient causes, and the existence of contingent beings. The existence of space and
time itself can be included among these and given the same logical treatment as these arguments with the same
result. I would go so far as to say that from the standpoint of pure reason, this type of logic may be the un-stated
reason for belief in God in the first place. How did it come to pass that anything exists at all? A first cause or a
necessary being seems to be required to explain the existence of the universe, and this is the very reason I have
never considered myself a complete atheist (although I have wanted to). Now, I will admit that belief in God is
usually not attributable to logical reasoning, and that for many people as well as the first of those in whom the
belief in God or any divinity came to be out of the desire for eternal life, justice, and so many other things that man
desires but finds lacking in the world. But having accepted that there may be no eternal life or concrete existence
of goodness or justice, I still hold to my belief in some sort of God for the very same type of reasoning formulated
by Aquinas in his cosmological argument—that for the existence of certain things we find in the world, including
the existence of the world itself, God is the only explanation.
And yet I can not accept this as an absolute certainty, as I am apparently a stronger fallibilist than I am a theist.
Every proposition, I believe, may be false, including the proposition that God must exist because the world exists.
The essence of the cosmological argument can be formulated as follows:
1. There exists a phenomenon X.Solid, seemingly infallible logic is never really infallible. Propositions 2 and 3 can both be denied. Something
2. Anything that exists must have a cause.
3. There can not be a chain of infinite causes.
4. For X to exist, there must be an ultimate cause Y (from 2 and 3)
5. Therefore Y exists (from 1 and 4), and this is God.
might exist uncaused. Though Aquinas would insist that God is the cause of Himself, one could easily interpret
God as an uncaused being, and thus the argument defeats itself. Proposition 3 is also not immune to doubt, as
though it may be inconceivable to our minds, the events of the universe may operate along a chain of infinite
causes. All universes may be the effect of events in other universes which were caused by other universes and so
on to infinity.
One may even go so far as to deny the third argument—that a necessary being must exist because otherwise there
would still be nothing in existence—and claim that there may have been a time when nothing really existed. I
would not accept this at all because of the absurdity it leads to—the very essence of non-existence is not to
exist, and therefore there must always be something in existence—but who is to say that reality or the universe or
whatever you might call it cannot admit of absurdities? As logical as the existence of a necessary being may be,
one may doubt the validity of logic itself, and in doing so eliminate all chance of this doubt being settled by logical
But going to this extreme is quite unnecessary, I believe, and goes well beyond the scope of the arguments I have
examined here. I would conclude that St. Thomas Aquinas ought to be credited with the best of the logical
arguments for God’s existence, but that in the end proof of God’s existence remains utterly impossible, and it will
always come down to a matter of faith.