3.1.1 - Arguments for God: Cosmological argument (Aquinas' Way 3)
Why is there anything contingent at all? In Aquinas' Third Way from the Summa Theologiae, beings that come into and pass out of existence cannot explain themselves, so the argument moves toward a necessary being. You will explain contingency, necessity, and the rejection of an infinite regress, then evaluate whether the chain really reaches the God of classical theism.
Problem And Terms
Aquinas' Third Way is a cosmological argument. That means it argues from features of the world to a conclusion about the existence of God. It is not a design argument about order and purpose, and it is not an ontological argument from the idea of God alone.
The Third Way begins with a simple observation: things in the world come into being and pass away. Humans, trees, animals, planets, institutions and artefacts do not exist by their own necessity. They exist, but they could have failed to exist.
Contingent Being
A contingent being is something that exists but does not have to exist. Its non-existence is possible, and its existence depends on conditions or causes beyond itself.
Necessary Being
A necessary being is not merely one more dependent thing. In Aquinas' argument, the final necessary being has necessity in itself and does not receive its necessity from another.
The key contrast is therefore not "caused things" against "uncaused things" in a loose everyday sense. It is contingent existence against necessary existence. Aquinas wants to show that contingent beings cannot be the whole explanation of reality.
For AQA AO1, do not reduce Way 3 to "everything has a cause". Its distinctive focus is contingency and necessity.
Aquinas Source Card
| Source | Claim | Why It Matters | Challenge To Watch |
|---|---|---|---|
| Thomas Aquinas, Summa Theologiae I, q.2, a.3 | Some things are possible to be and not to be; not everything can be like this; there must be something necessary in itself. | This is the official AQA named presentation for the cosmological argument. | The move from "a necessary being exists" to "this is God" needs careful explanation rather than a quick slogan. |
Aquinas writes within natural theology: the attempt to reason about God using human reason and features of the world, rather than relying only on revelation. This matters for AQA because the argument has a basis in observation: we observe changeable, perishable, dependent things, then reason from that fact to a necessary ground of existence.
The argument is also metaphysical. Aquinas is not doing modern physics or asking for the first event after the Big Bang. He is asking whether the existence of contingent things can be finally explained if everything is contingent.
Argument Chain
Aquinas' reasoning can be set out as a chain. Each step matters; if one step is missed, the argument becomes too vague to evaluate well.
| Step | Aquinas' Move | Meaning In Clear Language |
|---|---|---|
| 1 | Some things are possible to be and not to be. | We observe things that exist but could fail to exist. |
| 2 | Such things come into being and pass away. | Contingent things are not self-explanatory or everlasting by nature. |
| 3 | If everything were contingent, then at one time nothing would have existed. | Aquinas denies that a total reality made only of contingent things can be ultimate. |
| 4 | If nothing had existed, nothing could have begun to exist. | Non-being cannot produce being; something already existing is needed for anything to begin. |
| 5 | But things do exist now. | The "nothing ever exists" result is false. |
| 6 | Therefore not everything is contingent. | There must be at least one necessary reality. |
| 7 | A chain of necessary things whose necessity is received from another cannot regress infinitely. | Derived necessity still needs explanation. |
| 8 | Therefore there is something necessary in itself, causing necessity in others. | Aquinas identifies this self-necessary reality as God. |
This is why Way 3 is called the argument from contingency and necessity. The conclusion is not simply "the universe began, so God began it." It is that contingent existence points beyond itself to a necessary source.
Notice the two-stage shape:
- From contingent beings to a necessary being.
- From a necessary being to what Aquinas calls God.
That two-stage shape is useful for AO2 because the first stage may appear stronger than the second to some evaluators. A student can therefore judge the argument without treating it as either obviously successful or obviously worthless.
Necessity And Regress
Aquinas makes a subtle distinction inside the idea of necessity. He does not merely say "there is a necessary being" and stop.
| Type Of Necessity | What It Means | Why It Is Not Yet The Final Answer |
|---|---|---|
| Necessity received from another | A being may be necessary in some sense, but its necessity is explained by something else. | It still depends on another explanation. |
| Necessity in itself | A being has its necessity from itself, not from anything else. | This can end the regress of explanation. |
The regress problem is central. If every necessary being received its necessity from another, and that other from another, explanation would never reach anything that has necessity in itself. Aquinas thinks that this cannot provide a final explanation for why anything exists at all.
This is why the Third Way is stronger than a bare statement such as "something must have started it all." Aquinas is not merely looking for an earliest item in a timeline. He is looking for a reality that does not borrow its existence or necessity from anything else.
The word "God" at the end of the argument should therefore be read carefully. For Aquinas, God is the self-necessary source on which contingent and derivative realities depend. The Third Way on its own does not yet describe every attribute usually associated with God, such as goodness, knowledge or worship-worthiness. Those would require further reasoning.
Common Misunderstandings
Misunderstanding 1: "Aquinas says everything has a cause."
Way 3 is more precise than that. Aquinas argues that contingent beings need explanation and that a final explanation cannot itself be merely contingent or dependent.
Misunderstanding 2: "The argument is just about the beginning of the universe."
The Third Way is not only about a first moment in time. Even if a student imagined an everlasting universe, Aquinas' question would remain: why is there contingent existence rather than nothing?
Misunderstanding 3: "Necessary means scientifically impossible to destroy."
Necessity is a metaphysical idea here. A necessary being does not just happen to be very durable; it does not receive its existence from something else.
Misunderstanding 4: "The conclusion instantly proves every religious belief about God."
The argument aims to establish a self-necessary source of existence. Its value for religious faith is that it gives a rational basis for belief in God, but it does not by itself teach a whole doctrine of God.
These distinctions help keep AO1 accurate and make AO2 sharper. A weak paragraph attacks a simplified version of the argument. A stronger paragraph judges the argument Aquinas actually gives.
AO1 To AO2 Bridge
AQA expects students to understand the presentation of the argument and also to think about its strengths, weaknesses, status as a proof, value for religious faith, and relationship between reason and faith. For this presentation lesson, the evaluation should stay close to Way 3 itself.
| AO1 Content | AO2 Use |
|---|---|
| The argument begins from observed contingent things. | This gives it practical force because it starts from a shared feature of experience, not from scripture or a private revelation. |
| Aquinas argues that contingent beings cannot be the whole explanation of reality. | This can support the judgement that the argument answers a deep metaphysical question: why is there anything dependent at all? |
| The argument concludes with a being necessary in itself. | This is more than an ordinary cause, so it may avoid the simple objection "what caused God?" |
| The final move identifies the necessary being as God. | This is a pressure point: the argument may establish a necessary reality more clearly than it establishes the full God of religious faith. |
A balanced judgement might say: Way 3 has value because it gives a rational structure for moving from contingent existence to a necessary ground of existence. However, as a proof, its success depends on whether the move from contingent beings to a self-necessary being is accepted, and whether that necessary being can justifiably be identified with God.
This is not yet the Hume and Russell criticism lesson. It is the evaluative shape that prepares for that lesson: understand the argument first, then test whether its key moves hold.
Future Essay Use
For a future 10-mark AO1 answer, Way 3 can supply a developed explanation of Aquinas' cosmological argument:
- define contingent and necessary being
- show that the argument begins from observation
- set out the "if everything were contingent" reasoning
- explain why Aquinas rejects an infinite regress of derived necessity
- state the conclusion: a being necessary in itself, identified by Aquinas as God
For a future AO2 paragraph, Way 3 gives a focused judgement:
- strength: it asks a serious explanatory question about dependent existence
- limitation: it may only reach a thin idea of a necessary being
- careful conclusion: its value may be as rational support for faith, not as a proof that compels every thinker
Synoptic link: this lesson belongs to the C1-arguments-for-the-existence-of-god cluster. It will connect most directly with the sibling cosmological criticism lesson on Hume and Russell, and more broadly with AQA's questions about whether arguments for God are proofs, supports for faith, or unsuccessful attempts to reason beyond experience.