Aquinas’s Contingency Argument Part 3: Necessary Beings

This is the third and final post in a series on Aquinas’s Contingency Argument for the existence of God, also known as the Third Way. The argument that we laid out in the previous post goes like this:

  1. There are beings that exist which have the possibility to either exist or not exist (meaning that they have a natural tendency towards corruption or losing their form).
  2. Beings which have the possibility to either exist or not exist will necessarily, at some point in time, go out of existence (because given enough time, all natural tendencies are realized).
  3. If all beings are possible beings in this way, then, given infinite past time, all beings would have gone out of existence
  4. If all beings had gone out of existence, then nothing would exist now.
  5. But things do exist now
  6. So something, at least one thing, must exist which is impossible not to exist, a necessary being.

These premises were introduced and defended in the last post. I also mentioned there that there are two main branches of interpretation which take different routes. The argument above is the first interpretation. Its crucial distinctiveness lies in holding that we are assuming infinite past time, and that not only do all things individually have a tendency towards corruption, but that all things together have a tendency towards being corrupted together. The combination of these points assures us that if everything that exists is a possible being, then nothing would now exist.

The second branch of interoperation holds a somewhat different understanding. The main proponent of this line is the well known Thomistic scholar Brian Davies. The second branch does not assume infinite past time, and it does not focus on the “perishable” aspect of possible beings, i.e. their tendency towards non existence/corruption. Rather, it focuses on the generation or coming into existence of possible beings. So Davies writes:

“Aquinas, in his Third Way, can be read as arguing that not everything can be able to be and not to be because (i) all such things depend on something for their being there and (ii) without something not merely able to be and not to be there would be nothing at all. In the Third Way, so we may suggest, what Aquinas finds unbelievable is that everything is generated. He may be read as asking ‘How can everything be such that its coming into being depends on something else which has brought it about?” [1].

Again, generation does not mean absolute coming into existence out of nothing; it is not the creation of any new matter. Rather, generation is when a certain parcel of prime matter gains a new form. The new form instantiates the matter. Likewise, corruption is not absolute ceasing to exist, but rather just the loss of a current form, which is succeeded by the instantiation of a new form. Because prime matter is pure potency, it can gain any and all forms, but can only be instantiated with one form at a time, so it must lose its current form to gain another. Thus prime matter has a natural “metaphysical instability” as Ed Feser puts it, and this gives it a natural tendency towards losing its current form so that it can gain a new one. The first line of interpretation argued that all prime matter should be considered as a whole, and that it has an active tendency towards losing all its forms altogether, such that, if there were nothing to instantiate new forms, nothing would exist.

The second line of interpretation, however, wonders how all these things came about in the first place. In order to see this, we must first understand exactly why Aquinas refers to these as “possible” beings. On the face of it, calling something a “possible being” might sound a bit strange. Its actual meaning harkens back to the essence/existence distinction that we discussed for the Second Way (see here). Take a form of a physical object such as, say, a random tree. This form, before it is instantiated in matter, does not actually, physically exist; forms exist only in the objects they instantiate (contra Plato), or else in minds which grasp them. Thus this form cannot be said to have existence as intrinsic to its nature. For if existence is intrinsic to the nature of a form, then it will always have existence, and thus will always actually exist. But Aquinas’s whole point is that all the objects around us are most definitely not like that, because they are generated and corrupted all the time. If an object is generated and corruption, meaning that its form comes into and goes out of existence, then that means it does not always actually exist and so cannot have existence as intrinsic to its nature. A form that does not currently physically exist still, however, has the potential to exist, even if it does not actually do so. So this form can possibly exist, because its potential can be actualized; but it can also possibly not exist, because existence is not intrinsic to its nature and its potential for existence does not have to necessarily be actualized. It is, in Aquinas’s term, indifferent to existence or non-existence. But if that is the case, then there must be some explanation for why it does actually exist, rather than not; it must have some cause that has actualized its existence, instantiating it in matter.

But this immediately raises a profound problem: if everything that exists is possible in this way, then how does anything at all actually exist? Suppose, for illustration, that we aren’t talking about the entire universe, but rather a single marble. Suppose that this marble is the only physical thing that exists. Now, there are two possibilities: either this marble has always existed, or it came into existence. If it has always existed, then it is a necessary being and irrelevant to this argument. But if it has not always existed, then it was generated. But if it was generated, then before its generation its form did not actually, physically exist, and thus nothing at all actually, physically existed. And if nothing else existed to instantiate the marble’s form, then nothing at all would ever exist. But the marble does exist. The same is true for the set of all possible beings.

Now, we must be careful to make clear here that this interoperation of the argument does not necessarily rely, as the popular kalam argument does, on the universe having an absolute beginning. It could be, for example, that before the marble existed, the matter in which it would come to be instantiated had some other form which it then lost before gaining the form of the marble. And this arguably could in theory go back infinitely.

But remember that generation is essentially an instance of efficient causality, of a potency being actualized. In the previous post, we imagined all prime matter (which is pure potency) as one, whole, receptive “sheet” in which solid objects (forms) are dropped. But again, we are supposing a single marble is the entirety of physical existence, and prime matter can only receive one form at a time, so in order to receive the marble, it has to lose whatever object it is holding before. But once it has given up/lost that form, it is just pure potency, and cannot actualize anything on its own. How then could the next object come to be instantiated in it?

Now apply this same problem to the set of all existing possible objects. If this set is all that exists, and if this set by its very nature requires generation, then it never would have been able to be generated without some instantiating cause, and thus nothing at all would now exist. But things do exist, so the set of all existing possible objects cannot be all that exists. There must again be some being which is impossible not to exist, a necessary being.

In a sense, this second interoperation is really quite similar to the first, just considered from a different angle (generation rather than corruption). However, this interpretation does not require assuming infinite past time, because it is not arguing that existing possible things will go out of existence at some point, but that they would not have come into existence in the first place without at least one existing necessary being. This argument furthermore is somewhat similar to the essence/existence argument within the Second Way, and indeed could perhaps be interpreted just as that, for possible things by their nature do not have existence and thus must have been given existence by something which does have existence as its nature. The argument also implicitly assumes another distinct argument that could be labelled an “instantiating argument”, which is not actually one of the Five Ways; this argument I would rather discuss on its own in a future post.

But we are not finished yet, in fact we have only completed half the work. For we have established the existence of at least some “necessary” being, but we know nothing about it except that it cannot undergo generation and corruption. Indeed, some readers may be ready to point out an objection to the argument, the answering of which will provide a platform for the argument’s conclusion. For one might respond: wait a minute, why think that his necessary being is God? Even if we grant that all possible objects cannot be everything that exists, how do we know that all physical beings are also possible beings? Why not think that fundamental particles or matter, or space or energy or the fundamental forces, are the necessary beings?

Well, as a matter of fact, this response is correct. For Leibniz and others, God is the only necessary being. But Aquinas is not working with the same definitions. Aquinas thinks there are actually many necessary beings that are not God, including some physical things. Indeed, as you might have already considered, prime matter itself is necessary. But necessary just means not undergoing generation and corruption; it does not mean eternally self-existing. For once more, generation is not equivalent to absolute creation from nothing. Aquinas holds that things like angels, human souls, and even the physical heavenly bodies are all necessary beings, and yet they all were created from nothing at some point. Once existing, however, they do not generate or corrupt. This make sense, because generation and corruption involve gaining and losing forms; but angels, in Aquinas’s view, just are pure forms. How can something that is in itself a pure form gain or lose its form? Likewise, prime matter is pure potency, with no forms; how can something with no forms gain or lose its form? To emphasize once more in order to reduce confusion: all these things were definitely created, but once created they do not have a tendency to change forms. So, for instance, Aquinas says that physical heavenly bodies are necessary beings,

“because [their] matter has no potentiality in respect of another form, and the whole of its potentiality is determined by one form: such are the heavenly bodies in which there is no contrariety of forms. Accordingly a possibility of non-being is in the nature of those things alone whose matter is subject to contrariety of forms: whereas it belongs to other things by their nature to exist of necessity, all possibility of nonexistence being removed from their nature” [2].

Or in other words, because they matter in which their forms are instantiated are a “special” kind of matter that only has potency for that one form, so it cannot change forms. This is obviously incorrect given what we now know from astronomy and the physical sciences, but the point is just that there can exist many necessary beings, including, theoretically, physical ones (given what we know from modern science, I don’t think any physical beings actually are necessary, but that is irrelevant to the force of the argument).

Ed Feser explains this point more fully:

“A more promising strategy for the critic might seem to be to suggest (as J. L. Mackie does) that even if individual contingent things all go out of existence, there might still be some underlying stuff out of which they are made (a “permanent stock of matter” in Mackie’s words) which persists throughout every generation and corruption. Now if this were so, then what would follow, given the Aristotelian conception of necessity we’ve been describing, is that this stock of material stuff would itself count as a necessary being. But (so the suggestion continues) the critic could happily accept this (as Mackie does) given that such a “necessary being” would, in view of its material nature, clearly not be divine . . . In fact, as surprising at it might seem, Aquinas would be quite happy, at least for the sake of argument, to concede that the material world as a whole might be a kind of necessary being, in the relevant sense of being everlasting or non-transitory . . . Aquinas himself insists that while individual material things are generated and corrupted, matter and form themselves are (apart from special divine creation, to which he would not appeal for the purposes of the argument at hand lest he argue in a circle) not susceptible of generation and corruption. Far from regarding the notion of the material world as necessary as a blow to the project of the Third Way, Aquinas would in fact regard it as vindication of his claim that there must be a necessary being” [3].

For remember, the illustration of the marble was not meant to argue that the entirety of physical reality did in fact have a beginning; it was meant only to establish that if everything that exists is possible, then nothing would ever have come into existence, so not everything can be possible in this way. This is still theoretically compatible with an eternal material universe.

So Aquinas continues in his presentation of the Third Way in the Summa Theologiae with:

“Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary” [4].

We have now established our defense of this with two separate interpretations, both of which plausibly work. We will not advance to the conclusion of the argument:

“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” [5].

A necessary being is a being which, once it exists, does not undergo generation or corruption, having no tendency towards changing forms. It’s tendency is rather towards keeping and maintain its form in existence; it has a tendency towards permanence in existence. But this raises the question of the essence/existence distinction. The form of a necessary being has a tendency to continually exist. So either it contains existence as intrinsic to its nature, or existence is continually “added” to its nature, or the existence of the nature is continually sustained. If the former, then we have a self-existing, eternal, being; or, rather, we have Subsistent Being Itself, whose essence and existence are identical, which we established in our series on the Second Way is God. If the latter, meaning that existence is not intrinsic to its nature, then its essence is distinct from its act of existing. But this being still continually and permanently exists. So each and every moment existence must be given to/sustained in that being. And since this happens simultaneously each moment, we have an essentially ordered causal series, which cannot in principle have an infinite regress. Thus, even if we have non-divine or even physical necessary beings, we are taken back to an ultimate Necessary Being, whose necessity/permanence is within Himself, Subsistent Being Itself (I’m aware that if you have not read my previous series, much of what I’ve just said may not make any sense, and may even seem like unsubstantiated gibberish. But I am not merely asserting these things, I have already explained and defended them in detail several times over the past few series. If you have not already, please refer to them. Here is the article specifically on essence/existence. Here is the outline of the First Way, and here is the outline of the Second Way).

Since I’ve already established in the previous series that Subsistent Being Itself is also Pure Act, and that this Being is God, I will not further extrapolate on that. Instead I will make a few closing remarks on the distinctiveness of this the Third Way.

This argument does indeed converge on the Second Way, as it utilizes the essence/existence distinction employed therein. And the Second Way likewise converges in a sense on the First Way, sense the First Way establishes such conceptions as essentially ordered causal series and the Being of Pure Act, and the Second Way builds upon these. Altogether, the first three Ways form Aquinas’s three cosmological arguments. All three contain many similarities and even overlaps, but they also are distinct arguments, because they all begin from separate starting points: The First Way from motion, the Second Way from efficient causation in general, and the Third Way from the existence of possible beings. It makes sense that in the end they all ultimately converge, because the Being at which they arrive is Being Itself, the fundamental Reality and Existence that upholds and sustains all other reality. This Being is the ultimate source of all things, including motion, causality, and distinct forms, either possible or necessary.

That having been said, the Third Way is complex and extremely difficult to comprehend, much more so than the previous two ways. There is much that is debatable within it. But most of the criticisms I’ve encountered do not adequately grasp the fundamental metaphysics upon which the argument rests. These metaphysical principles are far from easy to understand, but once they are, the argument follows naturally from them. But one might still ask, what is the purpose of this argument? The previous two ways, especially the first, which Aquinas calls the “more manifest” argument for God’s existence, although they two are difficult and complicated, are still much simpler and clearer than the Third Way. If you’re trying to know whether God exists, would such a convoluted argument as the Third Way really be helpful? My answer is no, probably not, especially if you don’t already grasp the first two ways. Nevertheless, it is important, despite its extreme abstractness and difficulty, because it builds, expands, and gives a fuller depth to our understanding of reality. It also paints a kind of “hierarchical” structure within the first Three Ways. The First deals strictly with motion, the Second expands to include all efficient causality, of which motion is a type, and the Third expands to include all causality of transitory existence. Each “expansion” or step up the latter becomes a little more abstract, but also a little broader in its application, and gives us a richer picture of existence as a whole. It may not be  very useful as a popular “apologetic” argument, but for those looking for a deeper, more complete understanding of God’s existence, the Third Way surely will not disappoint.



[1]. Davies, Brian. “Aquinas’s Third Way.” New Blackfriars, vol. 82, no. 968, 2001, pp. 450–466. <>.

[2]. Aquinas, Thomas. Questiones Disputatae De Potentia Dei: On the Power of God. Translated by the English Dominican Fathers. Westminster, Maryland: The Newman Press, 1952, reprint of 1932. Html edition by Joseph Kenny, O.P. <;. Q. V, Article 3.

[3]. Feser, Edward. Aquinas. London: Oneworld Publications, 2009. Print, 95-96.

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

[5]. Ibid.


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