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The Argument from Contingency

From the existence of things that need not have been — contingent things — to a being whose existence is necessary. Its classic forms are Aquinas's Third Way and Leibniz's argument from the Principle of Sufficient Reason.

Premises & Hinge

The Argument

The numbered form is ours, after Pruss & Rasmussen · cf. the Stanford Encyclopedia of Philosophy, "Cosmological Argument" — the words themselves are the philosophers', below.

  1. P1 Contingent things exist — things that are, but might not have been.
  2. P2 Every fact — including the existence of the whole of contingent things — has a sufficient reason or explanation. the hinge
  3. P3 The totality of contingent things is itself contingent — it too might not have been.
  4. There is an explanation of that totality lying outside it: a necessary being, one that exists by its own nature.

The sources

The Argument Saint Thomas Aquinas 1274
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 corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by 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 thus even now nothing would be in existence—which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

Source — Saint Thomas Aquinas, Summa Theologica I, q. 2, a. 3 — the Third Way

Defence Gottfried Wilhelm Leibniz 1714
And that of sufficient reason, in virtue of which we hold that there can be no fact real or existing, no statement true, unless there be a sufficient reason why it should be so and not otherwise, although these reasons usually cannot be known by us.

Source — Gottfried Wilhelm Leibniz, The Monadology, §32

Continued Gottfried Wilhelm Leibniz 1714
Now this sufficient reason of the existence of the universe cannot be found in the sequence of contingent things … Thus the sufficient reason, which has no need of any other reason, must needs be outside of this sequence of contingent things and must be in a substance which is the cause of this sequence, or which is a necessary being, bearing in itself the reason of its own existence, otherwise we should not yet have a sufficient reason with which we could stop. And this ultimate reason of things is called God.

Source — Gottfried Wilhelm Leibniz, Principles of Nature and Grace, §8

Objection David Hume 1779
In such a chain, too, or succession of objects, each part is caused by that which preceded it, and causes that which succeeds it. Where then is the difficulty? But the whole, you say, wants a cause. I answer, that the uniting of these parts into a whole, like the uniting of several distinct countries into one kingdom, or several distinct members into one body, is performed merely by an arbitrary act of the mind, and has no influence on the nature of things.

Source — David Hume, Dialogues Concerning Natural Religion, Part IX (Cleanthes)

Objection Immanuel Kant 1781
The transcendental principle: "Everything that is contingent must have a cause"—a principle without significance, except in the sensuous world. For the purely intellectual conception of the contingent cannot produce any synthetical proposition, like that of causality … But in the present case it is employed to help us beyond the limits of its sphere.

Source — Immanuel Kant, Critique of Pure Reason — the impossibility of a cosmological proof

Reply Gottfried Wilhelm Leibniz 1697
From this it is manifest that even by supposing the eternity of the world, we cannot escape the ultimate extramundane reason of things, that is to say, God. Accordingly the reasons of the world lie hid in something extramundane, different from the concatenation of states or the series of things, the aggregate of which constitutes the world.

Source — Gottfried Wilhelm Leibniz, On the Ultimate Origination of Things (1697) — a reply to the objection that an eternal series needs no cause beyond itself

Argument hinges on:

The Principle of Sufficient Reason Every fact — including the existence of the whole of contingent things — has a sufficient reason or explanation. What does that mean?
The library's note

In everyday life we take the Principle for granted: nothing simply is the case for no reason at all. Your coffee is warm because it was heated; the window cracked because something struck it; you exist because your parents did. The Principle of Sufficient Reason generalizes this — for anything that exists or is true, there is some reason why it is so rather than otherwise, even a reason we may never discover.

To deny it is not to say the reason is merely hidden — it is to say there is no reason at all. Concretely: a brick could begin to exist in the middle of your living room, uncaused, with nothing whatever to account for it — not physics, not chance, nothing. A fire could start with no cause of any kind. And the deeper worry follows: if even one thing is allowed to be a brute fact like that, what still entitles us to demand an explanation for anything else?

Whether that is too high a price to pay — or whether, instead, holding to the Principle carries its own cost — is what the two columns below set side by side.

Written for this library — not a quoted source. It reports how the premise is argued and answered; the philosophers' own words are above.

If you accept it

If every contingent fact has an explanation, the conjunction of all contingent facts needs one too — and the only available candidate may make that conjunction necessary, so that nothing is truly contingent (the "modal collapse" worry).
Peter van Inwagen, An Essay on Free Will (1983) ↗

A restricted Principle of Sufficient Reason avoids the collapse: a necessary being can explain the contingent facts through a free choice that could have gone otherwise — an explanation that does not necessitate what it explains.
Alexander Pruss, The Principle of Sufficient Reason (2006) ↗

The reply

Defenders restrict the principle rather than abandon it, holding that contingent facts require explanation while necessary ones do not — which leaves free acts explained by reasons rather than necessitated by them.
Alexander Pruss & Joshua Rasmussen, Necessary Existence (Oxford, 2018) ↗

If you deny it

Deny it and you admit brute facts — things that simply obtain with no explanation at all; and without a sufficient reason, Leibniz holds, inquiry has no principled place to rest.
Leibniz, Principles of Nature and Grace §7 (Latta 1898)

Giving up the Principle threatens the ordinary explanatory reasoning we rely on everywhere else, since one must then draw an unprincipled line between facts that need explaining and facts that do not.
Michael Della Rocca, "PSR" (2010) ↗

Where it leads

Accept the Principle of Sufficient Reason, and this argument leads to a necessary being — one that exists by its own nature.

Beyond the public domain

The modern revivals and their critics are under copyright, so we don't host them — the reading doesn't stop at the public-domain record. Follow it at the sources:

Stanford Encyclopedia of Philosophy — Cosmological Argument Stanford Encyclopedia of Philosophy — Principle of Sufficient Reason Pruss & Rasmussen, Necessary Existence (Oxford, 2018)

You have read the premise, the objection, and the cost of each move. The library draws no conclusion.