Cosmological Argument

Reasoning from the world to God

The cosmological argument begins with the existence of the world and asks what ultimately explains it. We encounter things that change, have causes and depend on other things. Catholics who accept the argument reason that these cannot provide their own complete explanation: there must be an ultimate source of their existence and activity, which they identify as God.

This is a philosophical argument: it uses observations and reasoning rather than starting by asking someone to accept a religious text. It can therefore support Catholic faith and provide a basis for discussion with people who do not share that faith. Its focus is why things exist and have causes, rather than whether their design suggests a designer.

Thomas Aquinas, a Catholic theologian and philosopher, presented five ‘Ways’ of showing God’s existence in his Summa Theologiae. His First Three Ways are forms of cosmological argument. Each begins with something observable and reasons towards an ultimate explanation.

The First Way: change and an unmoved mover

Aquinas’ First Way begins with motion, meaning change as well as movement through space. Something that could become different is made actually different by something already able to bring about that change. Aquinas gives the example of fire making wood hot: the wood has the possibility of becoming hot, while the fire is already hot.

Aquinas argues that something cannot, in the same respect, be both the thing needing to change and the complete source of that change. The source of a change may itself depend on another source. For example, a stick moves because a hand moves it: the stick’s activity depends on something else.

Aquinas argues that a chain of dependent movers cannot explain change without an ultimate source. There must be a first or unmoved mover which brings about change without itself being moved by another. He identifies this as God.

The Second Way: causes and an uncaused first cause

The Second Way begins with efficient causes: things that bring about effects. Aquinas observes that causes produce effects, and that those causes may themselves depend on other causes.

Nothing can be its own efficient cause, he argues, because it would have to exist already in order to cause its own existence. Where an effect depends on a series of causes, removing the source of their causal activity would remove the effect too.

Aquinas therefore rejects an endless chain of dependent causes as a complete explanation. He concludes that there must be a first cause which does not receive its causal power from another. Catholics identify this uncaused cause as God.

Here, ‘first’ means an ultimate foundation, not simply the earliest event on a timeline. Aquinas’ argument should not be reduced to ‘the universe began, so someone must have started it’. His concern is whether dependent causes can explain themselves, even if the universe had always existed.

The Third Way: contingent and necessary existence

The Third Way begins with things that come into existence and pass away. A tree grows and eventually dies; it does not have to exist. Such things are contingent: they exist, but could fail to exist.

Aquinas argues that if everything could fail to exist, there could have been a time when nothing existed. If absolutely nothing existed, nothing could begin to exist, because there would be nothing already existing to bring it about. Yet things do exist.

He therefore concludes that not everything can be contingent: there must be something necessary, which cannot fail to exist. He then argues that the explanation cannot be an endless series of necessary things each receiving its necessity from another. Ultimately, there must be a being whose necessity comes from itself rather than from something else. Aquinas identifies this as God.

The central contrast is between things whose existence needs explaining and a being which does not depend on anything else for its existence.

What this means for Catholics

The First Three Ways present God as the unmoved mover, uncaused cause and necessary being. God is not another dependent object within the universe, but its ultimate foundation.

Catholics connect this with belief in God as creator and sustainer: everything ultimately depends on God, while God depends on nothing else. They understand God as eternal, without beginning or end, and powerful enough to account for the existence and activity of the universe.

This matters because it offers rational support for faith. Belief in a creator need not rest only on religious upbringing or an unexplained feeling. Aquinas held that people could reason from effects they know to a cause they cannot directly observe.

However, showing that an ultimate cause exists would not by itself establish every Catholic belief about God. These arguments alone do not demonstrate the Trinity or fully establish that God is loving. Aquinas recognised that reasoning from effects does not give complete knowledge of God’s nature.

‘Who caused God?’

An atheist or Humanist may object that if everything needs a cause, God must need one too. Exempting God can look like special pleading: making an exception simply to protect the conclusion.

The Catholic response is that the argument does not claim that absolutely everything has a cause. It concerns things that change or depend on something else. God is proposed as necessary and uncaused, rather than as one more dependent cause.

This answers the simple objection that the argument contradicts its own rule. Nevertheless, a critic can still ask whether there is sufficient reason to accept that such a necessary being exists, and why the ultimate explanation must be God rather than the universe itself. Defining God as necessary is not, on its own, proof that God exists.

Could science or an endless chain explain existence?

Atheists and Humanists may prefer natural explanations and argue that the Big Bang explains the universe’s early development without requiring God. They may also suggest that the universe has always existed, or that its ultimate origin is not yet understood. Lack of a complete scientific explanation does not automatically establish a religious one.

Catholics can respond that science and the cosmological argument address different questions. A scientific account describes natural processes; the philosophical argument asks why those processes and the universe exist at all. The Big Bang can be compatible with creation, but it does not itself prove that God caused it.

Similarly, Aquinas’ argument is not defeated simply by suggesting an everlasting universe. His objection is that even an endless series of dependent things would lack an ultimate explanation. Adding more dependent causes does not necessarily explain why there is any causal activity.

The disagreement therefore concerns whether reality must have an independent foundation. A critic may accept an endless chain, or regard the universe’s existence as a fact needing no further explanation. A Catholic may judge these answers incomplete.

Does an ultimate cause have to be the Catholic God?

A further objection is that even a successful argument for an ultimate cause does not clearly identify that cause as a personal, loving God. This is an important limitation: proving a foundation of existence is not the same as proving the whole of Catholic Christianity.

Catholics can reply that the argument is one part of a wider case for belief. It supports God’s independence and role as creator, while revelation and other arguments inform their fuller understanding of God.

A justified conclusion should therefore distinguish two questions: does the argument establish an ultimate explanation, and does it establish the Catholic understanding of God? Someone may find it persuasive on the first question while judging it insufficient on the second. Catholics can value it as rational support for faith without claiming that it answers every question about God.