Aquinas’s Contingency Argument Part 2: Contingent Beings

This is the second post in a series on Aquinas’s Argument from Contingency for the existence of God. In the Introduction, we discussed the different branches in the broader category of cosmological arguments for God’s existence; then we looked specifically at the Leibnizian contingency argument, emphasizing that it is completely different from Aquinas’s contingency argument, and that even though both refer to “contingent” and “necessary” beings, they don’t mean the same thing in both arguments.

Now, before we begin to lay out the argument itself, I’d like to make a quick comment. The Third Way is probably the most controversial/dubious of the Five Ways. For example, contemporary philosopher Robert Maydole writes that “The Third Way is not sound” and goes on to accuse it in several places of false premises and various logical fallacies [1]. However, Maydole does think the argument can be “modernized” via modal logic in order to make it arguably sound, but, as we shall discuss further on, his criticism, as well as the vast majority of modern critiques, completely misunderstand the actual argument. When the argument and its metaphysical foundations are really understood, I believe it is defensible. So let’s begin.

In contemporary philosophy, something is “contingent” if it could have been other than it is, and “necessary” if it must have been as it is. Or, as philosopher William Lane Craig explained it in a quote from the previous post:

“There are two kinds of being: necessary beings, which exist of their own nature and so have no external cause of their existence, and contingent beings, whose existence is accounted for by causal factors outside themselves. Numbers, sets, and other mathematical objects would be prime candidates for the first sort of thing, while familiar physical objects like people and planets and stars would be examples of the second kind of thing” [2].

In more technical terms, something is contingent if it exists in at least one possible world but not all possible worlds, and necessary if it exists in all possible worlds.

But how does Aquinas use the terms? Let’s take a look at his presentation of the argument in the Summa Theologiae:

“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” [3].

As can be seen, the word Aquinas actually uses is translated “possibility” rather than contingency, and this translation is beneficial, both as it makes it clear that we are referring to something distinct from contemporary use of “contingency”, and also gets at the truer meaning of what Aquinas is trying to say.

For Aquinas, the “possibility” of something has to do with the fact that it is generated and corrupted. Generation is not the absolute coming into existence of something, and corruption is not the absolute annihilation/ceasing to exist; but rather it is when a new form (essence/nature) is instantiated in matter. Or, in other words, generation is when a parcel of matter changes its form, gaining a new one; and corruption is when that parcel of matter loses its form. So if you take a tree, chop it down, and carve its wood into a table, no new matter has come into existence, but the existing matter has lost one form (that of a tree) and gained a new one (that of a table). The tree was corrupted, and the table was generated.

It’s important to note that for Aquinas, every physical thing that exists is a composite of matter and form. The basic, fundamental matter out of which everything is made, called “prime matter”, is pure potency. The matter has the potential to take any form. But no matter exists on its own without a form. Even things like atoms, electrons, neutrons, protons, quarks, etc., all have forms, and they’re all made out of prime matter. The form instantiates the matter, creating an object. This is called hylemorphism.

This is the point at which many modern thinkers misunderstand the argument. Consider what Robert Maydole has to say:

“The Third Way appears to have an empirical component which would distinguish it from all ontological and purely a priori arguments . . .  It turns out, however, that these observations of the natural world are not really essential to the logic of the Third Way, save in the trivial sense that observation might be required for the purpose of justifiably believing that something presently exists. Modality, not experience, is what gives promise to the Third Way” [4].

Here Maydole makes a completely unsubstantiated claim about the nature of the argument which entirely perverts Aquinas’s original intentions. It would be one thing to say, “I think the argument can be made better by being changed in this way”, which Maydole does say and do, and indeed his version of the argument is interesting and worth consideration in its own right. But it’s unfair to judge Aquinas on the basis of a standard which he wasn’t even using. The experiential aspects of the argument are not “trivial”, indeed they are what the whole argument is built upon. We perceive that objects around us are generated and corrupted all the time. What does this tell us? It tells us that it is part of the very nature of those objects to be generated and corrupted, not to exist indefinitely.

This is what Aquinas is referring to when he next says:

“But it is impossible for these always to exist, for that which is possible not to be at some time is not” [5].

Here Aquinas seems to make a curious claim, that if it is possible for something not to exist, then it will actually not exist at some point.

Consider now a criticism of this point from Maydole:

“It is true of course that things which are either generated or corrupted are things which can-not-be-at-some-time, simply because they do in fact fail to exist at some time. Things which are generated begin to exist at some time, and things which are corrupted cease to exist at some. Yet it fails to follow from this that things which can-not-be-at-some-time are things which in fact fail to exist at some time. They might fail to exist at some time in some possible world but always exist in the actual world. Matter-energy, for example, might in fact be eternal in the actual world, but either begin or cease to exist in some possible world” [6].

Philosopher Edward Feser discusses this type of objection in his book Aquinas:

“One common objection . . . is the suggestion that Aquinas commits an obvious fallacy when he claims that ‘that which is possible not to be at some time is not,’ for even if it is possible for something to go out of existence, it simply doesn’t follow that it will actually do so” [7].

The problem is that this objection follows an analysis based on modern conceptions of contingency, where something is contingent if it exists in at least one possible world but not all. So, Maydole says, why not just say that these “possible” beings exist in the actual world, but don’t exist in other possible worlds? If that is the case, there is no reason to think that at some point they will necessarily stop existing in the actual world. They could keep on existing forever in the actual world, but, because they only exist in some possible worlds, would still be considered contingent beings.

But that is precisely what Aquinas is not saying. Aquinas is not at all using the conceptual model of possible worlds. What he is saying is that a possible being is a being which is possible, in the actual world, to exist or not exist, given that it is actually generated and corrupted. But why think that what is merely possible, even in the actual world, will be actualized? Because the notion of possibility being employed here contains within it the idea of a tendency towards something. For example, a human child will have the natural tendency to grow into a human adult, and this natural tendency will automatically be actualized unless something prohibits it from doing so. In the same way, possible objects, says Aquinas, will naturally tend towards corruption. Why? Because of the very nature of their composition. Prime matter has the potency to take on any form, and so it will naturally tend to take on different forms. Since it can only instantiate one form at a time, it will naturally tend to lose whatever form it currently has and gain another. This is the process of generation and corruption. Feser writes:

“Given that the matter out of which the things of our experience is composed is inherently capable of taking on forms different from the ones it happens currently to instantiate, these things have a kind of inherent metaphysical instability that guarantees that they will at some point fail to exist. They have no potency or potential for changeless, indefinite existence; hence they cannot exist indefinitely” [8].

That last point is significant. Material objects do not have the potential to exist changelessly and indefinitely. Their very intrinsic essence is to change and to go through generation and corruption. And just as the possibility of the child to grow will automatically come about, so too will the possibility of an object to be corrupted (lose its form) automatically come about at some point. If things, by their very nature, have a tendency to/are directed to go out of existence, they will do so, unless something keeps them from doing so.

The argument continues from there:

“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” [9].

This is the crux of the entire argument, the make or break point which is criticized and even ridiculed by a large number of thinkers. Beyond this, even those who defend the argument are divided as to how exactly to interpret this point, such that two branches of defense have emerged, each taking the argument in a different direction. Both will be examined in this series.

Aquinas has already established that what is possible not to be at some point will not be, because it has a natural tendency to be corrupted. Now he seems to make a wild leap to the proposition that if all things are possible in this manner, then at some point all things will be corrupted, and nothing will exist. This, many claim, is not only completely unjustified, it is logically horrendous. Says Feser:

“It is widely held that his further inference . . . is clearly fallacious. Specifically, it is claimed that he is guilty here of a “quantifier shift” fallacy, of inhering from “Everything has some time at which it does not exist” to “There is some time at which everything does not exist.” This is called a “quantifier shift” fallacy because the quantifying expression “everything” shifts position from the first statement to the second” [10].

An example of the fallacy would be to say: “All humans have brains, therefore there is one brain which all humans have.” Which is obviously ridiculous.

So does Aquinas make this brutal mistake? Once again, not if we actually understand what is being said. An object with a natural tendency to go out of existence (where “go out of existence” means to be corrupted/lose its form), will at some point in time actually go out of existence. Therefore, if all objects have a natural tendency to go out of existence, then all objects will actually go out of existence at some point in time. This is valid. The only question is whether or not the time at which they all go out of existence will be the same time. This is where the supporters of the argument divide. The first branch argues yes, with two qualifications. First, we must suppose an infinite amount of time is given. Second, we must suppose that not only do all things individually have a tendency towards corruption, but that all things together have a tendency towards being corrupted together. Feser extrapolates:

“What Aquinas really seems to be getting at is the idea that given an infinite stretch of time, and given also the Aristotelian conception of necessity and possibility . . . then if it is even possible for every contingent thing to go out of existence together (which even Aquinas’s critic must concede), this possibility must actually come about. For (again, at least given an Aristotelian conception of possibility) it would be absurd to suggest both that it is possible for every contingent thing to go out of existence together, and yet that over even an infinite amount of time this will never in fact occur. “Possibility” here entails an inherent tendency, which must manifest itself given sufficient time, and an infinite amount of time is obviously more than sufficient” [11].

Renowned scholar Etienne Gilson also takes this view:

“If all beings can be born and perish, it would follow that at a given moment all beings would necessarily have perished. For . . . what is possible for a species, whose duration is eternal, must inevitable come to pass, otherwise the word possibility is in vain. Therefore, if disappearance were a true possible for all beings, considered as forming one sole species, they would have already disappeared . . . when the non-being of a thing is possible, there finally comes a moment when it does not exist. If therefore the non-being of everything were possible, there would have come a moment when nothing would have existed . . . [This] assumes . . . the eternity of the world . . . [It is] reasoning within the hypothesis that time is of infinite duration. Where there is infinite duration, it is unthinkable that a possible worthy of the name be not realized” [12].

There’s a lot in these quotes so we’ll spend some time unpacking them. First, the question might be raised, why in the world should we assume an infinite amount of time? Isn’t this a strange way for a philosopher arguing for the existence of the Christian God to proceed? One answer is that yes it would be strange, which is why Aquinas actually isn’t doing that. This is the answer of the second branch of interpretation, which we’ll look at later on. Feser and Gilson, and others, however, hold that on this view, Aquinas is assuming the eternity of the universe because that is what the majority of atheists would also believe, and he wanted an argument which could find common ground. In other words, the argument is set up like this: “If time is infinite, then the present argument works. If time is not infinite, then we have something like the kalam argument, which argues from the beginning of the universe to the existence of God. Either way takes us to God.” So yes, on this interpretation if time is finite then the argument doesn’t succeed. But if time is finite that sets up an entirely different argument, so it really doesn’t matter either way.

The other issue is still that of all things going out of existence “together.” Is it indeed possible (using the relevant sense of the term) for all contingent things to go out of existence together? Feser and Gilson suggest it is, since we can take all contingent things as one species, the entirety of which has the tendency towards corruption. However, let’s  first consider a few examples which might argue otherwise to see if this stands up.

Suppose, an objector of this point might put forth, we have an infinitely long chain of toppling dominoes. The chain goes backward and forward infinitely, with no beginning or end. Each individual domino is toppled by the proceeding domino, and it in turn, as it falls, topples the one after it. Couldn’t contingent beings be like this, where we just have an infinitely long overlapping series? The problem is that this analogy fails to account for the inherent, natural tendency of the objects. When dominoes are set up, they don’t fall over on their own. Either another domino, or gravity, or some other force has to operate to eventually topple them, but if we took away all of these things, the domino would presumably stay standing forever. Contrast this with contingent beings, which on their own tend towards “falling” out of existence. It would rather be like, instead of setting the domino up straight, we held it at a diagonal angle halfway between standing up straight and lying flat, and then let go. The domino automatically falls, without requiring other dominos to topple it. This is more akin to how contingent objects are (although even in this example gravity is acting on the domino externally). Now imagine that the entire  infinite chain of dominos is set up like this, and they are all at once let go. All of them will fall together.

But wait, you might wonder, if this is the case with contingent objects, then how come in our experience objects don’t go out of existence at the same time? Different objects are corrupted at different times all the time. This is plausibly because objects in our experience don’t exist independently; other objects are constantly interacting with and acting upon them, causing them to be corrupted sooner than they normally would be left to their own tendencies. Thus a baby mouse which is eaten my an owl dies much sooner than it would had it not been acted upon from an external agent. But even if no external agent had acted upon it, it would at some point have died anyways.

There is still one last possible objection, which relates to generation. It is true, you might grant, that all contingent objects are eventually corrupted. But objects in our experience, when they are corrupted, don’t just pop out of existence. Their present form is lost, but it is replaced by another form. So when a human dies, the form of “human” is replaced by the form of “corpse.” We could think of it in terms of reproduction. All humans die, but if a large number of humans reproduce, the human line will continue. So even though all human beings die individually at some point, because we reproduce it doesn’t follow that all humans collectively will die at the same time.

But this, Feser and Gilson would probably respond, still treats things as individuals, rather than as a species. They argue that not only does each individual thing have a possibility to go out of existence, but all things together, considered as one species, have an active tendency towards corruption.

To illustrate this, let’s use an extremely simplistic image. Think of prime matter as one, gigantic malleable plane or sheet that underlies everything. Now suppose that forms are solid objects that are dropped onto this sheet, and the sheet wraps around the solid object and takes its shape. Now, the sheet inherently has the tendency to “spit out” whatever object it currently possesses, to be replaced by another. And the time it takes for this to happen is affected by a vast, complex, intersecting network of external objects acting upon each other. So each little space on the sheet may be gaining and losing forms at its own, inconstant rate, that is different from the rest of the sheet, because of the various plethora of causal factors. New objects appear in the sheet all the time, and current objects are likewise lost. But the actual size of the sheet never changes. No new matter every appears or is lost.

How does this image help? Because instead of thinking of each individual contingent being as an individual parcel of matter tending to lose its form, we should think of prime matter as a whole having a tendency to lose all the forms that presently instantiate it–the entire sheet is “tossing up” its forms, if you will, all at once. But, you persist, as it loses all its forms, does it not gain new ones? Indeed, is not the very reason it has the tendency to lose its forms is so that it can instantiate new ones? Yes. But it cannot do so on its. Remember, prime matter is pure potency, which is actualized by the instantiation of forms. But it cannot actualize those forms in itself. Something else must actualize those forms in it, and that is Aquinas’s whole point. If prime matter has the tendency to lose all its forms, then if nothing else actualizes new forms, then nothing will exist at all. Prime matter is directed towards losing its forms, and if no new ones are instantiated, then nothing at all will exist. If time past is infinite, then at some point in the past this will have occurred, and nothing would now exist. But, obviously, things do exist now. So what does that mean? It means that not everything can be contingent. Not everything can possibly exist or not exist, having the tendency towards corruption. Something, at least one thing, must exist which is impossible not to exist. Something must exist which is necessary, not contingent.

The Third Way is probably the most complicated, difficult to understand argument for God’s existence I’ve ever studied. Even more so than the first two ways, it requires an in depth understanding of complex metaphysical principles. Even so, it is not as “laughably bad” as many modern thinkers make it out to be. I believe what has been established so far is defensible.

In the next post, we will trace the existence of a necessary being to the existence of God, as well as look at the second branch of interpretation of the argument.





[1]. Maydole, Robert E. “The Modal Third Way.” International Journal for Philosophy of Religion, 47: 1-28, 2000. The Netherlands: Kluwer Academic Publishers. <;.

Also found here:

[2]. Craig, William Lane. Reasonable Faith: Christian Truth and Apologetics. 3rd ed. Wheaton: Crossway, 2008. Print, 107.

[3]. Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook.

[4]. Maydole, Robert E. “The Modal Third Way.” International Journal for Philosophy of Religion, 47: 1-28, 2000. The Netherlands: Kluwer Academic Publishers. <;.

[5]. Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook.

[6]. Maydole, Robert E. “The Modal Third Way.” International Journal for Philosophy of Religion, 47: 1-28, 2000. The Netherlands: Kluwer Academic Publishers. <;.

[7]. Feser, Edward. Aquinas. London: Oneworld Publications, 2009. Print, 91.

[8]. Ibid., 92.

[9]. Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook.

[10]. Feser, Edward. Aquinas. London: Oneworld Publications, 2009. Print, 93.

[11]. Ibid., 94.

[12]. Gilson, Etienne. The Christian Philosophy of St. Thomas Aquinas. New York: Random House, 1956. Print. Online preview found here:


5 thoughts on “Aquinas’s Contingency Argument Part 2: Contingent Beings

  1. I have trouble with the inference that in an infinite past, there must have been a time when nothing existed. Why couldn’t it be the case that the time for nothing existing is to occur sometime in the infinite future, rather than in the infinite past? (admittedly, I also have trouble with the term ‘infinite.’)


    • Sorry for the delayed response. The conception of “infinite time” is indeed extremely difficult. Some philosophers, such as William Lane Craig, argue that an infinite amount of time is actually impossible in principle, because of certain paradoxes that seem to result from it. Others argue that, if past time were infinite, we would never arrive at the present moment. Needless to say, it’s very confusing to contemplate.
      For this argument specifically, the reason it is asserted that everything would already have gone out of time given infinite past time has to do with possibility. If a child has an inherent tendency (possibility) to grow into an adult, this tendency will automatically be actualized by a certain amount of time “X”. Now any certain amount of time X is a finite amount of time, because if it took an infinite amount of time for the tendency to be realized, then it never actually would be. The same is true of the inherent tendency of prime matter: it too will automatically be corrupted by a certain amount of time, which is necessarily finite. So, if past time is infinite, which means its stretches backwards forever and ever with absolutely no beginning, then of course that is literally infinitely more than enough time for an event which only requires a finite amount of time to be realized.


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