The Cosmological Argument for the Existence of God

The cosmological argument is a classical argument for the existence of God. It is also known as the first cause
argument. Unlike the ontological argument, it derives the
conclusion that God exists from a posteriori premise. The
argument is a posteriori because it is based on what can be seen
in the world and the universe.
The cosmological argument is based on the belief that there
is a first cause behind the existence of the universe (cosmos).
In its simplest form, the basic cosmological argument is based
on contingency and states that:
things come into existence because something has caused
 them to happen
things are caused to exist, but they do not have to exist
there is a chain of causes that goes back to the beginning
of time
time began with the creation of the universe
the universe came into existence about 15 billion years
there must have been a first cause, which brought the
universe into existence
this first cause must have necessary existence to cause the
contingent universe
God has necessary existence
therefore God is first cause of the contingent universe's

 The cosmological argument has taken many forms and has
been presented in many ways. In each form, the argument
focuses upon the causes that lead to the existence of things.
The argument appears to answer the questions:
How did the universe begin?
Why was the universe created?
Who created the universe?

Over the centuries, the terminology used by philosophers for the first cause of the universe has varied. Some philosophers
refer to the Creator of the universe as the 'First Cause' or
'First Mover'; others to a 'necessary being', or a 'self-existent
being' - and for many it is God.
The argument pre-dates Christianity. Plato developed one of
its earliest forms. He argued that the power to produce
movement logically comes before the power to receive it and
pass it on. In order for movement to occur in the first place,
there must be an uncaused cause to originate the movement.
Plato termed this uncaused cause the 'First Cause' or 'First

St Thomas Aquinas' Version

St Thomas Aquinas developed the most popular version of
the cosmological argument. He developed his Five Ways to
prove the existence of God, which he called 'demonstratio' for
the existence of God. He put these forward in the Summa
Theologica. The first three of his Five Ways form the
cosmological argument as a proof of the existence of God.
The three ways that support the argument are:
motion or change

The First Way is based on motion. In the world there are
things that are in motion, and whatever is in motion must
have been moved by something else. According to Aquinas,
this chain of movement cannot go back to infinity. There
' must have been a first, or Prime, Mover, which itself was
unmoved. The Unmoved Mover began the movement in
everything without actually being moved. Aquinas argued
that the Prime Mover is God:
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 moved is
moved by another, for nothing can be moved except it is in
' potentiality to that towards which it is moved; whereas a
thing moves inasmuch as it is in act. For motion is nothing
else than the reduction of something from potentiality to
actually, except by something in a state of actuality.

Aquinas was speaking of motion in the broadest sense. He included not only movement from one place to another, but
also movement in the sense of change of quality or quantity.
According to Aquinas, an object only moved when an
external force was applied to it.
He continued that objects only changed because some external
force had brought about the change. He spoke of filings
achieving their potential through an external influence.
Aquinas used the example of fire making wood hot. When
applied to wood, fire changes the wood to achieve its potential
to become hot. In order for a thing to change, actuality is
required. If it were not, a thing would have to initiate change
in itself, which would require that it was both actual and
potential at the same time. Aquinas considered this to be a
contradiction. For example, if wood could make itself hot then
it would be hot already. Wood cannot be hot to begin with;
otherwise, it would not change and become hot. The fact that
it is not hot already is its actuality. The fact that fire can make
it hot is its potentiality. In turn, something must have made the
fire change and become alight. Each change, therefore, is the
result of an earlier change. Aquinas, however, did not accept
that there was a series of infinite changes. He concluded that
there was a point at which the first movement (or change)
occurred, brought about by 'a first mover'. Therefore,
according to Aquinas, 'it is necessary to arrive at a first mover,
moved by no other; and this everyone understands to be God'.

In Aquinas' Second Way, he identified a series of causes and
effects in the universe. Aquinas observed that nothing can be
the cause of itself, as this would mean that it would have had
to exist before it existed. This would be a logical
impossibility. Aquinas rejected an infinite series of causes and
believed that there must have been a first, uncaused, cause.
This first cause started the chain of causes that have caused all
events to happen. This first cause was God:

The second way is from the nature of efficient cause. In the
world of sensible things 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 . . . Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
St Thomas Aquinas, Summa Theologica

Aquinas' Third Way identified the contingency of matter in
the universe. On the basis of the fact that things come into
existence and later cease to exist, Aquinas concluded that
there must have been a time when nothing existed. Therefore
the cause of the universe must be external to it and must
always have existed. There must have been a 'necessary being',
to bring everything else in to existence. Aquinas argued that
this 'necessary being' was God. He concluded that if God did
not exist, then nothing would exist:

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 be
corrupted, and consequently, it is possible for them to be and
not to be. But it is impossible for these always to exist, for
that which can not-be at the same time is not. Therefore if
everything can not-be, then at one time there was nothing in
existence. Now if this were true, even now there would be
nothing in existence because that which does not exist begins
to exist through 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 even now
nothing would be in existence - which is absurd . . . therefore
we cannot but admit the existence of some being having of
itself its own necessity, and not receiving it from another, but
rather causing in other their necessity. This all men speak of as
St Thomas Aquinas, Summa Theologica

From Philosophy of Religion by Jordan, Lockyer, Tate