Cosmological Arguments

The cosmological arguments are the family of a posteriori arguments for God that begin from the most general fact imaginable — that something exists, that there is a contingent world at all — and argue that this fact cannot be self-explanatory: it requires a being outside the series of dependent things, a first cause or necessary being, to account for it. Where the ontological argument reasons from a concept and the design argument from the world's order, the cosmological argument reasons from its sheer existence and contingency. It is the most resilient of the theistic arguments — versions run from Aristotle through Aquinas and Leibniz to a vigorous contemporary revival — because its starting datum is one no one can deny.

This page distinguishes the three sub-families (contingency, first-cause, and Kalām), states each carefully, and works through the standard objections: the assault on the Principle of Sufficient Reason, the Humean and Kantian critiques of causation, the fallacy of composition, the coherence of an actual infinite, and the "why not stop at the universe itself?" rejoinder.

Three families

The arguments share a skeleton — contingent/caused things exist → a regress of explanations cannot go on forever or in a circle → therefore a terminus of a special kind — but differ in what drives the regress and what the terminus is:

The first two are "vertical" — they concern a hierarchy of dependence that holds at each instant (a here-and-now causal sustaining), so the terminus is a being that grounds the world's existence now, and the argument does not need the world to have a beginning. The Kalām is "horizontal" — it concerns a temporal sequence reaching back, so it needs the universe to have begun and infers a cause of that beginning.

The argument from contingency (Leibniz)

Leibniz's version is the cleanest. It rests on the Principle of Sufficient Reason (PSR):

For every fact (or every truth, or every existing thing), there is a sufficient reason why it is so and not otherwise.

The argument:

1. Every contingent being has a sufficient reason for its existence (PSR).
2. The reason for a contingent being is either within it or in another being.
3. No contingent being contains the reason for its own existence (it might not have existed).
4. The totality of contingent beings is itself contingent (it might not have existed), so it too needs a reason.
5. This reason cannot lie within the totality (that would be circular) or in another contingent being (it would be part of the totality). So it must lie in a non-contingent — necessary — being, which exists by the necessity of its own nature.
6. This necessary being is God. ∎

The argument's power is that it does not depend on the world having a beginning; even an eternal contingent universe would still need a reason why it exists at all rather than nothing — Leibniz's famous question, "Why is there something rather than nothing?" The necessary being is invoked not as a first event in time but as the answer to that question.

The first-cause argument (Aquinas)

Aquinas's first three of the Five Ways (Summa Theologiae I, q.2) are cosmological. The First Way argues from motion (change): things are moved by others, and a regress of movers moved by another cannot be infinite, so there is a first Unmoved Mover. The Second Way runs the same structure on efficient causation: a first Uncaused Cause. The Third Way is a contingency argument (from "possibles" that come to be and pass away) to a necessary being.

The crucial and often-misunderstood point is that the regress Aquinas rejects is an essentially ordered (per se) causal series, not an accidentally ordered (per accidens) one:

• An accidental series is ordered in time, with each member's causal activity independent of its predecessor's continuing: a father begets a son who begets a grandson — the grandfather can die and the chain still runs. Aquinas does not claim such a series must be finite; he allowed (against most of his contemporaries) that the world might, for all philosophy can show, be eternal.
• An essential series is ordered in being, simultaneous, with each member exercising its causal power only because a prior member is here and now sustaining it: the hand moves the stick that moves the stone; the stone's motion derives entirely from a source it does not possess in itself. Such a series, Aquinas argues, cannot regress infinitely, because no member has the relevant power on its own — an infinite chain of borrowers with no lender never gets the loan. There must be a first member that has the power underivatively.

So the terminus is not a being that acted first long ago but one that sustains the dependent order at every moment — closer to Leibniz's necessary being than to a starting gun.

The Kalām cosmological argument

The Kalām (from the Arabic for the medieval Islamic "theology/dialectic") argument descends from al-Kindī and al-Ghazālī and was revived and made famous by William Lane Craig. Unlike the previous two, it does turn on the universe's having a beginning:

1. Whatever begins to exist has a cause.
2. The universe began to exist.
3. Therefore the universe has a cause.

Craig then argues, by conceptual analysis of what such a cause must be (causing the beginning of all space, time, and matter), that it is uncaused, beginningless, changeless, immaterial, timeless, spaceless, enormously powerful, and — since only a free agent can produce a temporal effect from a timeless state — personal.

The distinctive support is for premise 2, and comes in two forms:

• Philosophical: an actual infinite cannot exist in reality, because it generates absurdities — illustrated by Hilbert's Hotel, a hotel with infinitely many occupied rooms that can nonetheless accommodate infinitely many new guests (move the guest in room $n$ to room $2n$, freeing all odd rooms), and from which infinitely many guests can depart leaving the same number behind. If a beginningless past were real, it would be an actual infinite of elapsed events; so the past must be finite — the universe began.
• Scientific: the Big Bang cosmology, the thermodynamic arrow (a beginningless universe would already have reached equilibrium), and the Borde–Guth–Vilenkin theorem, which (Craig argues) shows that any universe with average positive expansion has a past boundary — a beginning — even granting inflation or a multiverse.

The objections

Each family inherits its own pressure points, and the modern debate is largely about these.

1. Against the Principle of Sufficient Reason

The PSR is the engine of the contingency argument, and it is the most attacked premise. Hume and, sharply, Russell (in his BBC debate with Copleston) reply that the demand for a sufficient reason can simply be refused:

"I should say that the universe is just there, and that's all." — Russell

The universe, or its existence, may be a brute fact — something with no explanation at all. Worse, a strong PSR (every fact has an explanation) seems to entail that every truth is necessary (van Inwagen's argument: if the conjunction of all contingent truths had an explanation, that explanation would itself be contingent and so part of the conjunction, explaining itself — impossible — or necessary, making all contingent truths necessary, collapsing contingency). The theist's reply is to weaken the PSR (to contingent existing things rather than all facts) or to argue that "the universe is just there" is not an explanation but a refusal to explain, and that refusing to explain the most striking fact of all is intellectually arbitrary.

2. Against causation (Hume, Kant)

The first-cause and Kalām arguments assume robust principles of causation. Hume argued that we can conceive an event without a cause (we can imagine something beginning to exist ex nihilo without contradiction), so "everything that begins has a cause" is not a necessary truth but at best an empirical generalisation — and one we have no warrant to extend to the beginning of the universe, an event utterly unlike the within-universe causings from which we learned the principle. Kant added that causality is a category of the understanding that structures our experience of the phenomenal world; applying it beyond all possible experience, to a first cause of the world as a whole, is an illegitimate transcendent use of reason that generates antinomies (he held one could prove both that the world has and has not a beginning).

3. The fallacy of composition

The contingency argument moves from "each contingent thing needs a cause" to "the totality of contingent things needs a cause." Critics (Hume, Russell) charge a fallacy of composition: inferring a property of the whole from the same property of each part, like arguing that because every brick is small the wall is small, or because every human has a mother the human race has a mother. Perhaps each thing in the universe is caused by another thing in the universe, and the series as a whole needs no external cause — every member is explained, so nothing is left over to explain. The theist replies that this commits the converse error: explaining each member by another member leaves the existence of the whole series unexplained — Leibniz's point that even an infinite chain of contingent things is still a contingent chain whose existence is not thereby accounted for. Whether "the existence of the totality" is a genuine further fact needing explanation, or an illusion of double-counting, is the crux.

4. The actual infinite and "why not the universe?"

Against the Kalām specifically: many philosophers and mathematicians deny that actual infinites are impossible. Since Cantor, the transfinite is a consistent and central part of mathematics; Hilbert's Hotel is counterintuitive but not contradictory — it shows only that infinite sets behave unlike finite ones (a proper subset can be equinumerous with the whole), which is a theorem, not a paradox. If actual infinites are possible, a beginningless past cannot be ruled out a priori, and premise 2 must rest entirely on contested empirical cosmology (and the BGV theorem's interpretation is disputed; quantum-gravity models with no initial boundary exist).

Against all the families is the "why not stop at the universe itself?" objection: every cosmological argument reaches a terminus that is itself unexplained — an uncaused cause, a necessary being whose necessity is just asserted. If we are permitted to halt the regress at a being whose existence requires no further explanation, why not halt it one step earlier, at the universe, and treat it as the necessary or brute terminus? The theist's answer is that the universe is manifestly contingent (it could have been otherwise, or not existed) and composite/changing, whereas only a being that exists by its own nature — necessary, simple, immutable (see aseity and simplicity) — is the kind of thing that could be a genuine stopping point. Whether that distinction is principled or ad hoc is the perennial standoff.

Where the cosmological argument sits

The cosmological argument is the most durable theistic argument because its premise — that a contingent world exists — is undeniable, and its conclusion — a necessary, self-existent ground of that world — captures something close to the core of the classical concept of God (aseity, necessity). Its fate turns on two deep and unresolved questions of general metaphysics, not on anything peculiar to religion: whether the Principle of Sufficient Reason holds or the world's existence is a brute fact, and whether the regress of explanation must, or even can, terminate in something other than the universe itself. Even granting it full success, the argument delivers only a necessary first cause — it is silent about that being's goodness, knowledge, or concern, which is why it is typically run alongside the teleological and moral arguments in a cumulative case, and why the problem of evil remains untouched by it.