The modal cosmological argument or “argument from contingency” is the argument from the contingency of the world or universe to the existence of God. The argument from contingency is the most prominent form of cosmological argument historically. The classical statements of the cosmological argument in the works of Plato, of Aquinas, and of Leibniz are generally statements of the modal form of the argument.
What distinguishes the modal cosmological argument from the kalam cosmological argument is that it is consistent with the idea that the universe has an infinite past. The kalam cosmological argument rests on the controversial claim that the universe has a beginning in time. The argument from contingency, in contrast, is consistent with the universe having existed from eternity.
The argument from contingency draws on the distinction between things that exist necessarily and things that exist contingently.
Something is “necessary” if it could not possibly have failed to exist. The laws of mathematics are often thought to be necessary. It is plausible to say that mathematical truths such as two and two making four hold irrespective of the way that the world is. Even if the world were radically different, it seems, two and two would still make four. God, too, is often thought to be a necessary being, i.e. a being that logically could not have failed to exist.
Something is “contingent” if it is not necessary, i.e. if it could have failed to exist. Most things seem to exist contingently. All of the human artefacts around us might not have existed; for each one of them, whoever made it might have decided not to do so. Their existence, therefore, is contingent. You and I, too, might not have existed; our respective parents might never have met, or might have decided not to have children, or might have decided to have children at a different time. Our existence, therefore, is contingent. Even the world around us seems to be contingent; the universe might have developed in such a way that none of the observable stars and planets existed at all.
The argument from contingency rests on the claim that the universe, as a whole, is contingent. It is not only the case, the argument suggests, that each of the things around is us contingent; it is also the case that the whole, all of those things taken together, is contingent. It might have been the case that nothing existed at all. The state of affairs in which nothing existed at all is a logically possible state of affairs, even though it is not the actual state of affairs.
It is this that the argument from contingency takes to be significant. It is because it is thought that the universe exists contingently that its existence is thought to require explanation. If the universe might not have existed, then why does it exist? Proponents of the cosmological argument suggest that questions like this always have answers. The existence of things that are necessary does not require explanation; their non-existence is impossible. The existence of anything contingent, however, does require explanation. They might not have existed, and so there must be some reason that they do so.
Critics of the argument from contingency have sometimes questioned whether the universe is contingent, but it remains at least plausible to think that it is so.
The only adequate explanation of the existence of the contingent universe, the argument from contingency suggests, is that there exists a necessary being on which its existence it rests. For the existence of the contingent universe must rest on something, and if it rested on some contingent being then that contingent being too would require some explanation of its existence. The ultimate explanation of the existence of all things, therefore, must be the existence of some necessary being. This necessary being is readily identified by proponents of the cosmological argument as God.
The argument from contingency, then, can be summarised as follows:
The Argument from Contingency
(1) Everything that exists contingently has a reason for its existence.
(2) The universe exists contingently.
(3) The universe has a reason for its existence.
(4) If the universe has a reason for its existence then that reason is God.
(5) God exists.