Spiritual Life
Reasons to Believe
Religions & Sects
Church History
In the News
Faith & Reason Press Speaker's Forum Links Resources About Us

Overview of the Cosmological Argument

William Lane Craig

In contrast to the ontological argument, the cosmological argument assumes that something exists and argues from the existence of that thing to the existence of a First Cause or a Sufficient Reason of the cosmos. This argument has its roots in Plato and Aristotle and was developed by medieval Islamic, Jewish, and Christian thinkers. It has been defended by such great minds as Plato, Aristotle, ibn Sina, al-Ghazali, ibn Rushd, Maimonides, Anselm, Aquinas, Scotus, Descartes, Spinoza, Berkeley, Locke, and Leibniz. The cosmological argument is really a family of different proofs, which can be conveniently grouped under three main types.


The kalam cosmological argument originated in the attempts of Christian thinkers to rebut Aristotle’s doctrine of the eternity of the universe and was developed by medieval look at the formulation of this argument by al-Ghazali (1058-1111). He reasons, “Every being which begins has a cause for its beginning; now the world is a being which begins; therefore, it possesses a cause for its beginning.”1 In support of the first premise, that every being that begins has a cause for its beginning, Ghazali reasons: anything that begins to exist does so at a certain moment of time. But since, prior to the thing’s existence, all moments are alike, there must be some cause that determines that the thing comes to exist at the moment rather than earlier or later. Thus, anything that comes to exist must have a cause.

The second premise is that the world, or the universe, began to exist. In support of this premise Ghazali argues that it is impossible that there should be an infinite regress of events in time, that is to say, that the series of past events should be beginningless. He gives several reasons for this conclusion. For one thing, the series of past events comes to an end in the present–but the infinite cannot come to an end. It might be pointed out that even though the series of events has at one end in the present, it can still be infinite in the other direction because it has no beginning. But Ghazali’s point may be that if the series is infinite going back into the past, then how could the present moment arrive? For it is impossible to cross the infinite to get to today. So today could never arrive, which is absurd, for here we are! Second, if the number of past events were infinite, that would lead to infinites of different sizes. For suppose Jupiter completes an orbit once every twelve years and Saturn once every thirty years and the sphere of the stars once every thirty-six thousand years. If the universe is eternal then each of these bodies has completed an infinite number of orbits, and yet one will have completed twice as many or thousands of times as many orbits as another, which is absurd. Finally, if we take the orbits completed by just one of these planets, we may ask, is the number of orbits it has completed odd or even? It would have to be one or the other, and yet it is absurd to say the infinite is odd or even. For these reasons, the universe must have had a beginning.

Therefore, the universe must have a cause of its beginning, which Ghazali identifies with God, the Eternal.

Thomas Aquinas

The Thomist cosmological argument is based on the impossibility of an infinite regress of simultaneously operating causes. It seeks a Cause that is First, not in the temporal sense, but in the sense of rank or source. Although Thomas Aquinas (1225-74) did not originate this line of reasoning, he is famous for his clear summary of it in his Five Ways of proving that God exists.2 We shall look at his first three ways, which are different versions of the argument for a First Cause.

The First Way is the proof for an Unmoved Mover based on motion. We see in the world that things are in motion. But anything that is in motion is being moved by something else. For a thing that has the potential to move cannot actualize its own potential; some other thing must cause it to move. But this other things is also being moved by something else, and that is also being moved by something else, and so on. Now this series of things being moved by other things cannot go on to infinity. For in such a series, the intermediate causes have no power of their own but are mere instruments of a first cause. It is important to keep in mind that Aquinas is thinking here of causes that all act simultaneously, like the gears of a machine, not successively, like falling dominoes. So if you take away the first cause, all you have left are the powerless instrumental causes. It does not matter if you have infinity of such causes; they still could not cause anything. Aquinas contend, in effect, that a watch could not run without a spring even if it had an infinite number of gears, or that a train could not move without an engine even if it had an infinite number of box cars. There must be a first cause of motion in every causal series. For all self-moving things–including humans, animals, and plants–this would be the individual soul, which is an unmoved mover. But souls themselves come to be and pass away and thus cannot account for the eternal motion of the heavenly spheres. In order to account for this cosmic motion, we must postulate an absolutely Unmoved Mover, the First Cause of all motion, and this is God.

The Second Way attempts to prove the existence of a First Cause of existence based on causation in the world. We observe that causes are ordered in series. Now nothing can be self-caused, because then it would have to bestow existence on itself, which is impossible. Everything that is caused is therefore caused by something else. Aquinas thinks here of the same sort of simultaneous causal series as he did in the First Way, except that here the causes are of existence, not motion. The existence of any object depends on a whole array of contemporary causes, of which each in turn depends on other causes, and so forth. But such a causal series cannot go on to infinity, for the same reason I explained above. Therefore, there must be a First Cause of the existence of everything else, which is simply uncaused; and this everyone calls “God.”

The Third way is the proof for an Absolutely Necessary Being based on the existence of possible beings. We see in the world beings whose existence is not necessary but only possible. That is to say, these beings do not have to exist, for we see them come to be and pass away. If they were necessary, they would always exist. But all beings cannot be merely possible beings, for if everything were merely possible, then at some point in time everything would cease to exist. Aquinas here presupposes the past eternity of the world and appears to reason that in infinite time all possibilities would be realized. Hence, if every being, including matter i8tself, were only a possible being, then it is possible that nothing would exist. Thus, given infinite past time, this possibility would be realized and nothing would exist. But then nothing would now exist either, since out of nothing, nothing comes. Since this is obviously absurd, not all beings must be possible beings. Some being or beings must be necessary. In fact, Aquinas believed that there were many necessary beings: the heavenly bodies, angels, even matter itself. Now, he continues, where do these necessary beings get their necessity–from themselves or from another? Thomas here distinguishes between a thing’s essence and existence. A thing’s essence is its nature, that set of properties which it must possess in order to be what it is. For example, the essence of man is “rational animal.” If anything lacked either of these properties, it would not be a man. A thing’s existence, on the other hand, is its being. Now if a being is not necessary in itself, this means that its essence is distinct from its existence. It does not belong to its nature to exist. For example, I could think of the nature of an angel without ever knowing whether or not an angel actually exists. Its essence is distinct from its existence. Hence, if such a being is to exist, something else must conjoin to its essence an act of existence. Then it would exist. But there cannot be an infinite regress of necessary beings that get their existence from another. (The reasoning is the same as that in the First Way, against an infinite regress.) So there must be a First Being, which is absolutely necessary in itself. In this Being, essence and existence are not distinct; in some mysterious way its nature is existence. Hence, according to Aquinas, God is Being itself subsisting (ipsum esse subsistens). God is pure Being and is the source of being to everything else, whose essences do not involve their existing.

G.W.F. Leibniz

The Leibnizian cosmological argument was developed by the German mathematician and philosopher G.W.F. Leibniz (1646-1716) and is often confused with the Thomist cosmological argument. But Leibniz does not argue for the existence of an Uncaused Cause, but for the existence of a Sufficient Reason for the universe.3 The difference will become clear as we proceed.

“The first question which should rightly be asked,” wrote Leibniz, “will be, Why is there something rather than nothing?” That is, why does anything at all exist? There must be an answer to this question, because “nothing happens without a sufficient reason.”4 Leibniz’s famous Principle of Sufficient Reason holds that there must be a reason or rational explanation for the existence of one state of affairs rather than another. Why does the universe exist? The reason cannot be found in any single thing in the universe, for these are contingent themselves and do not have to exist. Nor is the reason to be found in the whole aggregate of such things, for the world is just the collection of these contingent beings and is therefore itself contingent. Nor can the reason be found in the prior causes of things, for these are just past states of the universe and do not explain why there are any such states, any universe, at all. Leibniz asks us to imagine that a series of geometry books has been copied from eternity; such an infinite regress would still not explain why such books exist at all. But the same is true with regard to past states of the world: even should these be infinite, there is no sufficient reason for the existence of an eternal universe. Therefore, the reason for the universe’s existence must be found outside the universe, in a being whose sufficient reason is self-contained; it is its own sufficient reason for existing and is the reason the universe exists as well. This Sufficient Reason of all things is God, whose own existence is to be explained only by reference to Himself. That is to say, God