Plantinga and Aquinas on the Viability of the ‘Third Way’

Abstract

This article deals with Alvin Plantinga’s arguments against St. Thomas Aquinas’s third way to show that God exists. Although attacks on this argument have come from Christians and non-Christians, my contention is that these rebuttals of the third way arise because of a misunderstanding of the argument itself. Thus, the metaphysical background for understanding the third way is first explained, and then the arguments Plantinga raises against it are dealt with. After reading this article it should be clear that the third way to show God’s existence is plausible and that Plantinga’s attacks against it are based on a straw man rather than the substantive argument the third way actually is.

Both Christian and atheist have attacked Aquinas’s third way, an argument for God’s existence. In order to refute Aquinas’s argument, one must first understand it. Many modern critics have not understood the argument.1 Consequently, they do not attack Aquinas’s argument, but a caricature, and commit the straw man fallacy. In this paper, I will explain the third way, in order to disabuse their misunderstanding. In order to do so, I will do the following: section one will explain the metaphysical background needed to understand the third way; section two will explain the third way; section three will present Alvin Plantinga’s criticisms of the third way; section four will defend Aquinas’s third way against the aforementioned criticisms; section five will contrast the underlying presuppositions of Aquinas and Plantinga. As a result, one will see that Plantinga is just another person among the many who have not understood the third way.

1. The Metaphysical Background

It is important to know what the word actuality means in Aquinas for two reasons: (1) Aquinas divides being into actual and potential; (2) Aquinas’s division of being is essential to understanding the third way. Thus, what did Aquinas mean by actuality? Actuality is associated with the idea of activity or action. In contrast, a thing can be said to potentially act before it actually does. A person who can potentially run is not running. If a person is running, they do not have the potential to run, but they do have the potential to stop. One can think of actuality and potency as opposed. Something cannot be both actually doing something and potentially doing the same thing at the same time. In other words, someone cannot be actually reading and potentially reading at the same time. Thus, the distinction between act and potency can be compared to existence and non-existence. Joseph Owens, an expert in Aquinas’s metaphysics explains, “To be made actual was to be made to exist, either in reality or in cognition. While actuality for Aristotle was located in form, for Aquinas it is found primarily in existence, and anywhere else only through existence.” (Owens 1979). This articulation is advanced in the first of 24 Thomistic theses which states: “Potency and Act so divide being that whatsoever exists either is a Pure Act, or is necessarily composed of Potency and Act, as to its primordial and intrinsic principles.”2

As emphasized in 20th century Thomists such as Etienne Gilson, Joseph Owens, and R. Garrigou-Lagrange, Pure Act is found in God alone, who is existence. W. Norris Clarke explains, “The one ultimate utterly simple fullness of perfection must be the Pure Act of Existence itself, Subsistent Existence itself (Ipsum Esse Subsistens).” Whereas all the rest of creation, from angelic beings down to rocks have existence, God is existence. Created beings have existence via receiving this act of existing from God. Receiving an act of existence is called participation in the Thomistic conception. As St. Thomas explains: “To participate is to receive, as it were, a part; and therefore when anything receives in a particular manner that which belongs to another in its totality, it is said to participate in it.” (Aquinas 1998).

If a person exists (i.e., has the act of existence), then as long as they receive this act, they lack potential not to exist. An act of existence in creatures is limited by the nature of the creature receiving it. This is true even for angelic beings. This type of being would be composed of essence and its act of existence. The essence of this composition would be the limiting potency to the act of existing. As it relates to the overall structure of reality, the conception that St. Thomas envisages is comprised of various proportions of act and potency throughout all of reality, with the pure being of God at the highest level.

The aforementioned distinction between potency and act leads to the explanation about the primacy of actuality (Aquinas 1945, Q. 4. Art. 1, ad. 3). One way to think about the primacy of actuality emphasizes that existence precedes operation (Aquinas 1955, chap. 15.4). In other words, a person cannot do anything (operate) unless they exist. The act of existence, the first or primary act received by creatures, is that by which they exist. After creation, a creature can operate, which is the second act. Thus, if I tell you about the men who sailed across the ocean and who had the fear of falling off the edge of the world, we presuppose these men exist. If they did not exist, they could not have sailed, and neither could they have feared. Thus, the act of existence and act of operation are distinguished as first and second acts, respectively. The difference between these acts leads to Aquinas’s distinction between existence and essence.

There are many examples that may be used to illustrate this distinction. If a person asks about something’s essence, they want to know what it is. However, if a person asks about something’s existence, they want to know whether it is. For example, if I told a person that some scientists claim that the coelacanth is a missing link in the evolutionary chain, they may ask, “What the heck is a coelacanth?” To which I reply, “It is a fish.” The person who asks what a coelacanth is wants to know its essence. However, a person can also ask the question, “Are there any coelacanth alive?” The person who asks this question obviously wants to know whether these fish currently exist.

For Aquinas, creatures have a real distinction between their existence and essence. One can ask and understand what a creature is without knowing whether it is. One can ask this question because the essence of a creature does not contain its existence. For example, I can tell you what a unicorn is without telling you whether there are any existing unicorns. Furthermore, this distinction also notes that creatures are created as composed of the act of existence and their essence. The essence of a creature limits its act of existence. To clarify, picture someone filling up a balloon with air. The way the balloon limits the air that is filling it up is similar to the way the essence limits the act of existence.3 As the essence limits the act of existence in creatures, essence is potency to the act of existence.4 Thus, for Aquinas, all creatures are composed of essence and existence (Aquinas 1968). As W. Norris Clarke explains,

Thus essence is to the act of existence as limiting potency to act in the order of qualitative perfection; matter is to form as another mode of potency limiting the actuality of form by pinning it down to here and not there in the quantitative order of spatial extension…; substance is to accident as receptive and limiting potency to the whole range of accidental perfections open to successive participation by this particular kind of being.

(Clarke 2001, p. 157)

From this we can see how the distinction between essence and existence applies to creatures in Aquinas. The essence of creatures limits the act of existence.

How does this apply to God? In Aquinas’s conception, God has no real distinction between His existence and essence. This means that God’s essence is His existence. There is no difference. Although there are many reasons Aquinas gave for this conclusion, I will only present one. The conclusion that God is not composed comes from the metaphysical reasoning that leads to God’s simplicity. There is at least one type of being that exists. My own existence is as a composed being. However, every composed being is composed by something else. Furthermore, one cannot go on to infinity seeking an ultimate composer of the composed beings, because it leads to an infinite regress. Therefore, there must be a being that is an uncomposed composer. An uncomposed being is a simple being. From this reasoning, one can conclude there are at two types of beings: simple and composed beings. There is no composition in the existence and essence of the simple being; there is composition of existence and essence in composed beings. Thus, God is a simple being with no distinction between His essence and existence. Building on knowing the difference between these two types of beings, we will now turn to the difference between necessary and possible beings.

In the third way, Aquinas explains that there are two types of beings: (1) possible and (2) necessary. The word possible here may be thought of in a variety of ways. Pinning down the correct definition is important for understanding the argument. Etienne Gilson explains,

It may mean the simple absence of inner contradiction in an essence, and in such cases, all non-contradictory combinations of essences are equally possible, but none of them is one step nearer its actualization than another one. It may also mean that an essence is fully determined, so that it is actually capable of existing. Such possibles are in the condition which Scholastics would have called that of proximate potency to existence. But such a possibility still remains pure abstract possibility… The possibility of its essence does not include that of its existence, unless, of course, we count among its required conditions the very existence of its cause. But, if we do, the being of the cause is the reason why the possible is a possible being. Omne ens ex ente: all being comes from another being, that is not from a possible, but from an existent.

(Gilson 1949, pp. 210–11)

A possible being does not necessarily exist until it is filled with an act of existence from an already existing thing.5 One can say a possible being is indifferent to either existing or not existing. All created beings are possible beings. As created beings, possible beings cannot account for their own existence. Possible beings are composed of the act of existence and their essence. As possible beings are composed, and their essence is not existence, they must receive the act of existence at every moment. Thus, all possible beings, which are receiving the act of existence, are dependent on something else for their existence (Garrigou-Lagrange 1946). Note on this explanation that currently existing things can therefore be possible in one sense, and necessary in another, as effects that have received an act of existence. They are dependent on a necessary being in receiving their act of existence. A necessary being’s essence is existence.

One may recall that, for Aquinas, this is the description of God. He is not composed. God not only composes all possible beings, but he sustains them in existence each moment after He creates them. Thus, if there is a possible being, then there is a necessary being. To clarify, as long as I am typing this, then an arrangement of words are being created to communicate a message. If I stop typing at any moment, then the words will also stop. Thus, the words appearing on the page are dependent on me continuing to type. In a similar way, a possible being’s act of existence is dependent on receiving existence from a necessary being.

2. The Third Way Explained

Having explicated Aquinas’s metaphysics, I will now explain the third way. This is the third way as it appears in the Summa Theologica:

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 be corrupted, and consequently, it is possible for them to be and not to be. But it is impossible for these always to exist, for that which can not-be at some time is not. Therefore, if everything can not-be, then at one time there was nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist begins to exist only through something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist- 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 already been proved in regard to efficient causes. Therefore, we cannot but admit the existence of some being having of itself its own necessity. This all men speak of as God.

(Aquinas 1945, Q. 2, Art. 3)

There are four steps to this argument and I will explain each. (1) There are possible beings. (2) A possible being only begins to exist when composed. (3) If all beings were composed, nothing would ever exist. (4) Therefore, not all beings are composed, and there is a necessary being.

First, there are possible beings. Possible beings are beings that are composed. Composed beings, which are constituted of act and potency, can change. Generation and corruption are types of change that only occur in composed beings. Only a being that already exists causes a possible being to exist. Thus, generation only occurs to a possible being. There are possible beings that can corrupt since composed of form and matter. This would include all the material things you can see. If a possible being, which is composed, decomposes, then it corrupts. As generation and corruption are evident to all people, there are possible beings.

Second, it is impossible for possible beings to always exist, for that which is composed at some time does not exist. The reason for this is because possible beings are composed. It takes a composer to compose possible beings. Possible beings are composed of essence and an act of existence. It takes a prior being to compose a possible being, since a possible being could not compose itself. A being would have to exist and not exist at the same time to compose itself. Neither could a composed being have always existed. A possible being needs to be composed before it can exist. There is more going on here too, as this possible being is also currently being sustained in existence, to exist now.

Third, if everything is a possible being, then at one time there was nothing in existence, and there would still be nothing in existence. A possible being, composed of essence and the act of existence, cannot account for its existence. If only possible beings exist, then there would still be nothing in existence, as they cannot account for their composition or continued existing. If there were only possible beings, none of which account for their own existence, even now nothing would exist. Aquinas’s statement is reminiscent of the verse from The Sound of Music, “Nothing comes from nothing, nothing ever could.”

Some may misunderstand this point. There is often a confusion between a causal chain in the past and a causal chain that exists right now. This is sometimes distinguished between explaining the difference between an accidentally ordered series and a causal chain that is essentially ordered. Those familiar with arguments for God’s existence can note that the Kalaam argument for God’s existence argues to the finite past creation of the universe in what may be thought of as a horizontal and accidental series of causes. Examples of an accidentally ordered series of causes could be children and their parents, or an author and his writings. Even after the parents or an author perishes, what they have made may remain. This is different from an essentially ordered series of causes that are simultaneous with the effect. The classical example is a person moving a rock with a stick. We may also think of someone typing words, communicating a message, running, or even a train engine pulling cars. If not for the mover simultaneously providing the action, the effect would not take place. This also means Big Bang cosmology has no implications on the vertical argument of the third way, but it could affect the Kalaam argument, which is horizontally going into the past.

Let us now look at the claim that not everything is a possible being. If there are possible beings, there must be a necessary being that exists. A necessary being is needed to account for possible beings. A being that is a necessary effect is a dependent being because it depends on its cause. A dependent being cannot account for its own existence. One cannot have an infinite regress of necessary effects without a cause as the ground of their being. The cause that grounds the being of all the necessary effects or contingent beings is a necessary being. A necessary being is simple and not composed. This being, which accounts for the existence and composition of all other beings, is God.

Let us make clear something here about the wording in this part of the argument. We have already established that Aquinas says some possible beings are those which are corruptible. Clearly these can be or not be, due to their material conditions and the fact they can change. They are composed beings. However, there is another group of possible beings which are not composed of matter, but are composed of their essence and act of existence. These are also possible beings considered from the perspective of their composition of essence and existence. These are what Christian metaphysicians have called angelic beings. There is an efficient cause which is sustaining them in existence that is necessary and pure act.

Think of how this explanation unpacks some of Aquinas’s understanding of participation. The contingent or possible being participates in an act of existence it receives from the one necessary being. The essence of the possible being limits this act of existence. The necessary being is the superior source that provides for the continued existence of possible beings.

To summarize, Aquinas argues that possible or composed beings only begin to exist when composed. If all beings were composed then either an infinite regress would ensue, or nothing would begin to exist. Yet, both of these options are absurd. Therefore, there must be a necessary being that is the uncomposed composer.6

Some may dispute the aforementioned interpretation of the third way laid out in this paper. Despite objections to this interpretation, it has a long history among Thomists. Consider three major thinkers that interpret Aquinas to be saying this very thing. First, R. Garrigou-Lagrange explains the third way as follows:

If there exist contingent beings, which can cease to exist, then there must be a necessary being which cannot cease to exist, which of itself has existence, and which, here and now, gives existence to these contingent beings. If once nothing at all existed, there would not be now, or ever, anything at all in existence. To suppose all things contingent, that is, of themselves non-existent, is to suppose an absurdity.

(Garrigou-Lagrange 1950, p. 75)

Another Thomist, Frederick Copleston, follows a similar explication of the third way:

The third proof, which Maimonides took over from Avicenna and developed, starts from the fact that some beings come into existence and perish, which shows they can not be and can be, that they are contingent and not necessary, since if they were necessary they would always have existed and would neither come into being nor pass away. St. Thomas then argues that there must exist a necessary being, which is the reason why contingent beings come into existence. If there were no necessary being, nothing at all would exist.

(Copleston 1962, pp. 60–62)

Much of this understanding is based on the distinction between necessary and contingent beings. One must parse out this distinction to truly understand the third way.

Of course it must be admitted that one can generally grasp the distinction between necessary and contingent things as implying a causal connection between them. For the argument of the third way, there is the language of possible beings, and a necessary being. The necessary being argued for in the third way is God. He is the one who has being through Himself, meaning His essence is existence. Aquinas speaks of possible beings also. Possible beings are indifferent to existing or not existing. Excluded from the realm of possible beings would be married bachelors or four-sided triangles. Some of these possibles are those things that corrupt due to being composed of matter. The necessary being concluded in the third way is the one necessary in himself. It must be remembered that Aquinas is taking this argument from Avicenna, who discusses the necessary being and the possible beings. The doctrine of creation, says the great Muslim Aristotelian philosopher Averroes who explains the distinction of Avicenna, “that the heavenly bodies are necessary by another, and yet possible out of themselves.” (Averroes 1562, Disp. I, Vol. IX, f. 9). This is also addressed by St. Thomas in Question 44, Art. 1 in the Summa Theologica. This question addresses the objection of things that are created, and even the types of necessary things, as to whether they can not-be. We learn from this question the following three important points Aquinas wants us to take away:

• God is self-subsisting being itself (and only one)
• All other beings are beings by participation and are caused by one First being
• There are some necessary things which are necessary because they are effects of an efficient cause (Aquinas 1945, Q. 44., Art. 1)

It is to be noted that some things are considered as necessary by another or ab alio, and are not necessary in themselves as God is. They are necessary effects, which can be considered from different viewpoints. As previously explained, separated substances are composed of an act of existence and their essence. Angels then can be listed among the possibles in the order of existence because they do not exist in themselves, but only through God. Some think of angels as being necessary beings to which one may conclude, but the text of Aquinas makes clear that only God has necessity in Himself as the primary cause. However, in the Thomistic framework these too are dependent for their current existing on God’s sustaining them in existence via a concurrent act. God is the efficient cause of all things that currently exist.

3. Plantinga’s Understanding of the Third Way

This section explains how Plantinga views the third way, and the charges that Plantinga levels against it. Plantinga’s book God and Other Minds will be the primary text used for his understanding of the argument and his criticisms of it. Although it is important to point out that Plantinga’s main arguments are against a logically necessary being, he does present some arguments against what I will call a metaphysically necessary being.

After presenting the third way, Plantinga writes that the parts of the argument that trouble him include the relationship between what he calls premise 2, which he formulates as “Whatever can fail to exist, at some time does not exist,” and premise 3, which is “Therefore, if all beings are contingent, then at one time nothing existed.” (Plantinga 1967, p. 5). These two premises are taken from the section of the third way that says, “But it is impossible for these always to exist, for that which can not-be at some time is not. Therefore, if everything can not-be, then at one time there was nothing in existence.” How are these premises to be interpreted? Plantinga rightly suggests that before they can be interpreted one must have a proper understanding of what Aquinas means by the modal terms the argument contains (ibid., p. 6). Specifically, if a person is going to understand this argument, then it is essential to understand how the terms necessary and contingent are being used. How does Plantinga think the terms are being used?

According to Plantinga, Aquinas must be using the term necessary to mean logically necessary. Where does he get this idea? On the one hand he explains that Aquinas and his commentators say little about how they are using the modal terms necessary and contingent (ibid.). But, on the other he finds evidence that this argument is talking about logical necessity from Question II, Article 1 in the Summa Theologica. Plantinga writes:

In Question II, Article 1, he [Aquinas] points out that some propositions self-evident in themselves are not self-evident to us. A proposition is self-evident in itself, Aquinas says, if its subject contains its predicate; this characterization indicates pretty clearly that he takes these propositions to be necessarily true. Since, therefore, he maintains that the proposition God exists is self-evident in itself (but not to us), it is fairly clear that he takes the proposition to be logically necessary; and hence it is initially plausible to suppose that in the third way he sets out to demonstrate the existence of a logically necessary being.

(ibid.)

Thus, for these reasons, Plantinga will deal with the refutation of a logically necessary being in this argument. However, even after he proposes that Aquinas is describing a logically necessary being, the question still needs to be asked, what does it mean for a being to be necessary for Plantinga?

In God and Other Minds a necessary being is described as one that could not be caused to come into existence and cannot have a beginning of its existence (ibid., p. 8). Also, one cannot suggest “a necessary being has its necessity caused by another in case that other acts upon it in some specifiable way.” (ibid.). In God, Freedom, and Evil a necessary being is the opposite of a contingent being (Plantinga 1974a, p. 78). Since a contingent being can exist or not exist, that must mean a necessary being cannot not exist (ibid.). For Plantinga, “A necessary being exists in every possible world.” (ibid.).

Furthermore, in his chapter on the cosmological argument, Plantinga attacks the being that belongs to what he calls the “Geach–Brown interpretation.” Throughout most of the chapter Plantinga dismembers the concept of a logically necessary being as he conceives it is presented in the third way. When dealing with the second alternative, the “Geach–Brown interpretation”, he presents no argument against their distinctions between beings necessary in themselves and beings that have their necessity caused by another because he says the distinction is hard to grasp. Furthermore, Geach and Brown overlook that “there is the fact that on Aquinas’ view God is a logically necessary being.” (Plantinga 1967, p. 23). The most important argument against the metaphysical conception of the third way, according to Plantinga, is the difficulty that arises from premises 2 (Whatever can fail to exist at some time does not exist) and 3 (If all beings are contingent then at one time nothing existed) (ibid., p. 24). This argument is the only one Plantinga mentions. According to Plantinga, these premises are not self-evident, and 3 does not follow from 2. Plantinga concludes that even if this argument does work, it does not prove the existence of God, but only the existence of a necessary being, which could be the universe (ibid., p. 25). Is it the case that we should conclude with Plantinga that this piece of natural theology is ineffective?7

4. Responding to Plantinga

In this section, I will respond to Plantinga’s criticism of the third way. First, I will explain the difference between logical and metaphysical necessity. Then, I will give four arguments against the assertion that Aquinas is referring to a logically necessary being. Last, I will give answers to his arguments against a metaphysically necessary being.

If a proposition is logically necessary then it is a tautology. For example, it is logically necessary that A=A (the law of identity). In propositional form this looks like, ‘man is man’, or ‘if a man is 5 feet tall, then he has height’, or ‘if Alvin Plantinga is mountain climbing, then he is at a particular altitude’. In these examples the subject and predicate are based on identity (ibid., p. 157). It is logically necessary that a genus is included in a species, such as blue includes color. This distinction between genus and species is simply a result of the activity of the mind. For example, one can see the concept of height is contained in the subject five feet tall. It is logically necessary that when the premises of a logical argument are valid, then the conclusion necessarily follows. Logically necessary propositions are propositions whose predicate adds nothing to the subject. Moreover, if one were to deny something that is logically necessary, it would result in a contradiction.8 There is simply a necessary connection between the terms in the proposition based on identity. How does this differ and how is it like metaphysical necessity?

Just as logical necessity is a connection between terms, metaphysical necessity is said to be a connection between things. Logical and metaphysical necessities are alike in that they are both concerned with connection. They are different in what they are referring to. Logical necessity alone does not tell us about the existence of anything. Existence or being properly belongs to the realm of metaphysics. From this one can see that metaphysical necessity is concerned with the necessary connection between one thing and another. In contrast, unlike something that is logically necessary, to deny that something is metaphysically necessary does not always result in a contradiction. Thus, logical necessity deals with relationships in the mind and metaphysical necessity deals with relationships in reality.9 If something is metaphysically necessary, it cannot not-be. What are some different ways the term metaphysical necessity can be applied?

There are two ways a thing can be said to be metaphysically necessary: because of its nature or because it is an effect. Only God is metaphysically necessary because of His nature. For Aquinas a metaphysically necessary being would be God. He has no potential to come to be or to cease to be. A metaphysically necessary being, if there is one, must exist and has no potential not to exist. A metaphysically necessary being would have no potential and would be completely actual. A second way a thing is metaphysically necessary is if there is a causal sequence, then there is a necessary connection between the cause and effect. The causal elements involved in a sequence act to cause a change. The definition of change is the actualization of potency, insofar as it is in potency. In other words, all effects must move from a state of potentiality to actuality by something already in act. For example, suppose you throw a snowball at my head. The snowball has the potential to hit my head (assuming you have good aim) until it actually smashes against my cheek. At this point my head will bend to the side as I feel the icy snowball strike its target. In this example, you (already in act) caused the snowball to hit me (at the point of contact I move from being potentially creamed by a snowball to actually being creamed). It is impossible for an effect to cause itself. A thing would have to be in act and not be in act at the same time and in the same sense; an evident contradiction. How is this principle explained in terms of existence?

The principle of causality can be understood using the terms existence, act, and potency. Existence cannot be non-existence (being is not non-being); in the same way that act is not potency. Only something that exists can cause another to exist. In the same way, only what is actually can cause what is potentially to be actually.10 Thus, all effects must be caused by definition. It is metaphysically necessary that every effect have a cause. One can apply this principle to a possible (contingent) being. A possible being (that can not exist) does not necessarily exist. If a thing is in potency, it can only be made actual by something actual.11 Furthermore, a possible being is dependent for its existence on a necessary being. It is metaphysically necessary that if a possible being exists, a necessary being exists. With these distinctions in mind, let us now turn to Plantinga’s charge that Aquinas is referring to a logically necessary being.

Why does Plantinga assume that Aquinas is referring to a logically necessary being? His reasons for doing so are drawn from the Summa where Aquinas writes,

No one can mentally admit the opposite of what is self-evident, as the Philosopher states concerning the first principles of demonstration. But the opposite of the proposition God is can be mentally admitted: The fool said in his heart, There is no God (Ps. Lii. I). Therefore, that God exists is not self-evident… Yet, granted that everyone understands that by this name God is signified something than which nothing greater can be thought, nevertheless, it does not therefore follow that he understands what the name signifies actually, but only that it exists mentally.

(Aquinas 1945, Q. 2, Art. 1)

However, given this passage it seems very clear from what has been said about logical necessity that Aquinas cannot be referring to logical necessity. For something that is logically necessary is both self-evident and would entail a contradiction if it were denied. However, as Aquinas points out, the opposite of the proposition God is can be mentally admitted, unlike something that is logically contradictory. This is the first good reason for not believing this is referring to logical necessity. Are there other reasons?

Consider another to show that Aquinas is not referring to a logically necessary being. One is that logical necessity only deals with connections between terms. However, Aquinas is not dealing only with terms in his argument. He is talking about existing things. Certainly, Aquinas is trying to prove the actual existence of a necessary being. As has already been explained, he is explaining that the connection between things points to metaphysical necessity. A second point is that it is anachronistic to say that Aquinas is only using the term necessary being to refer to a logically necessary proposition. Philosopher James Ross points out that, not only did Aquinas think of what is logically necessary is self-evident, but also that

It is inaccurate to excise Thomas’s term from context where it is used as a property (or more properly as a modality of existence and not of propositions) and apply it to propositions. Thomas, and all philosophers who have claimed the name ‘Empiricist’, realized that it is one thing to say: ‘this proposition is necessarily true’ and entirely another to say ‘this fact is necessarily so.’.

(Ross 1961)

Yet, to his credit, Plantinga rightly states that Thomas makes the distinction between things that are evident in themselves, but not to us, and things that are evident in themselves and to us (ibid.). Unfortunately, one may question how seriously Plantinga takes this observation about Aquinas’s distinction. It seems that, since the proposition “God exists” is not a first principle that is undeniable, such as the law of contradiction or the law of identity, then people can deny it without contradiction. Furthermore, Thomas points out that it is because God’s essence is existence, which he will prove in Question 3, the proposition God exists is evident in itself. Thus, it seems that he is pointing to a metaphysical necessity of God being existence that makes the proposition true in itself but not evident to us. If this proposition was simply logically necessary, then it could not be denied because it would be based on first principles and it would only be referring to terms, not things.

One final point against thinking that Aquinas was referring to a logically necessary being is the textual evidence. Thomas criticizes Anselm for trying to argue for a logically necessary being in Question 2, Article 1; in the same question that is quoted by Plantinga. Thomas says that Anselm made the mistake in the ontological argument of moving from the concept of the thing in the mind (which he thought was logically necessary), to the existence of the thing in reality. According to Aquinas, this ontological argument provides no metaphysical grounds to proceed from the existence of something in the mind to the existence of something in reality based solely on propositions. Therefore, the arguments Plantinga gives to support the interpretation that for Aquinas God is a logically necessary being seem to crumble once one examines the text. Yet, if this is the case, all the arguments that Plantinga presents against a logically necessary being in the third way are not really arguing against Aquinas. However, Plantinga does present some arguments that can be taken to be against understanding this as a metaphysical argument for God. What are these arguments?

The three arguments Plantinga gives against a metaphysical understanding of the third way are based on the relationship between his formulation of premise 2 (whatever can fail to exist, at some time does not exist) and premise 3 (Therefore, if all beings are contingent, then at one time nothing existed). Plantinga’s three arguments are: (1) These premises are not self-evident. (2) Premise 3 does not follow from 2 (non-sequitur). (3) The argument does not conclude to God but only the universe. How would Aquinas respond to Plantinga’s three arguments against the third way?

To the first argument, Aquinas would give two answers. (1) The premises are not self-evident in the sense of being logically necessary. It is not contradictory to deny these premises. This does not mean that these premises are not evident in some other way. (2) Aquinas would assert that these premises are metaphysically necessary. Once a person understands the metaphysics behind the argument, these premises are evident.

Second, Aquinas would explain that premise 3 does follow from 2. Premise 2 says, “Whatever can fail to exist, at some time does not exist.” The principle that this premise describes is that if a thing needs to be composed before it actually exists, then prior to being composed a thing does not exist. Analogously, suppose you ask when a State of the Union speech began. This speech would not start until the orator begins. It also only continues as long as the orator speaks. In the same way, possible beings do not begin to exist until they are composed. This composition itself indicates not only that prior to being combined with the act of existence, it didn’t exist, but that even now it cannot account for its current existing.

Next, premise 3 says, “if all beings are contingent, then at one time nothing existed.” While some suggest this is an obvious case of the quantifier shift fallacy, one need not interpret this in such a way that it does so.12 Premise 3 is based on the same principle as premise 2. It is not only the case that everything that is composed does not exist before being composed, but in the case of possible beings, even now they would not exist if not being sustained in their existence. The principle that everything composed needs a composer leads to an uncomposed composer. Yet, in this scenario, there is no uncomposed composer, but only composed, possible beings. All possible beings must be composed both prior to their existing and currently due to still existing. Therefore, due to the impossibility of an infinite regress, if all are composed, possible beings, not only would it be the case that at one time nothing existed, but even now nothing would exist.

This is precisely the line of reasoning some philosophers are trying to revive from the third way.13 Here is a recent formulation of the argument:

• There are dependent beings.
• If there are dependent beings, then their existence must be continually sustained by something else.
• If dependent beings are continually sustained by something else, then either the chain of continually sustained dependent beings regresses infinitely or terminates in an independent being not itself sustained.
• The chain of sustained dependent beings cannot regress infinitely.
• Therefore, the chain of continually sustained dependent beings must terminate in an independent being that is not itself sustained (Hsiao and Sanders 2021).

This argument rejects the idea of existential inertia. Existential inertia indicates that if a possible being has existence, it simply will continue to exist without something sustaining it.

There are two problems with existential inertia from a Thomistic perspective. If existence were part of the nature of a possible being, then it would not cease to exist. Nobody would admit this for possible beings as everyone has experienced many that do pass out of existence. However, existence also cannot be accidental to a thing, as accidents such as Aristotle’s categories only exist in things that already exist. Existence is an act received in possible beings. In their article explaining the contingency argument, Tim Hsiao and Gil Sanders explain:

Existence must be an activity in the same way that change is an activity. When a person walks down the hall, he is changing in location. Change itself is not some thing out there, so it would be incorrect to say that change is what you attach to your feet. Change only describes a process. Similarly, existence describes the process of being made actual at every moment. It may be helpful to think of existence as a power generator and a TV as that which receives its power. A TV is constantly receiving new power from the power generator in order for it to continue operating.

(ibid., p. 3)

What can be made of those discussing a mathematical infinite series or series stretching back in time? Keep in mind that in these series, which can be thought of as horizontal, these are indeed the subject that Aquinas submits cannot be proven philosophically. Aquinas has in mind here a vertical dependent series. Frederick Copleston explains about St. Thomas on this point,

What he denies is the possibility of an infinite series in the order of actually depending causes, of an infinite ‘vertical’ series. Suppose that the world had actually been created from eternity. There would be an infinite horizontal or historic series, but the whole series would consist of contingent beings, for the fact of its being without beginning does not make it necessary. The whole series, therefore, must depend on something outside the series. But if you ascend upwards, without ever coming to a stop, you have no explanation of the existence of the series: one must conclude with the existence of a being which is not itself dependent.

(Copleston 1950, vol. 2, part 2, pp. 341–42)

This is the line of reasoning that Aquinas is using that rules out any infinite set of possible beings to account for the current existing of anything. There is an ontological dependence the entire realm of possible beings has on a necessary being. No possible or contingent being can even account for its own existence, as the act of existence is something added to its nature. A fortiori, possible beings cannot account for the existence of others. One must not confuse Aquinas’s argument here of an essentially ordered series where the effect is simultaneous with the cause sustaining it in existence and an accidentally ordered series such as parents who produce offspring. In the accidentally ordered series, even after the parents are gone the offspring continues. One can thus concur with St. Thomas’s assertion about the philosophical difficulties present in a backward accidental series through time and hold that is not what he is asserting here in the third way.14

There is also the problem with referring to time as it relates to the third way and possible beings as opposed to God as a necessary being. Necessary being has all sorts of attributes such as timelessness as being pure act or actus purus. Possible beings are limited, and one finds, as George Klubertanz explains in his Introduction to The Philosophy of Being, for possible beings, “the act of existing is limited by the potency in which it is received.” (Klubertanz 1963, p. 134). One characteristic of some possible beings is that they are subject to time in that there is a before and after, while necessary being is not. This article is suggesting adopting a metaphysical understanding of the third way as it relates to our conception of God and explained in those attributes immediately after the five ways are offered in the Summa. Thomistic philosopher Norman Kretzmann explains according to Aquinas’s argument that God must exist and cannot be (highlighting a few among nineteen predicates he lists), “anything that begins or ceases to exist, temporal, dependent for its existence, imperfect, composite in any way, [and] anything whose being is other than its nature.” (Kretzmann 1997, p. 118). Given the existence of possible beings subject to time, there must be a necessary being sustaining them in existence that is beyond time and pure act. Therefore, while some work has been done on modal understandings and temporal terms such as before or once, a more metaphysical approach that deals with what is necessary to account for the dependence of things right now is what I am suggesting should be the focus of the third way.

There are a number of ways to understand the implications of the necessary being that is pure act. As Joseph Owens explains,

Pure act will be substance, but incorporeal substance. Substance as directly known to human cognition is corporeal. But anything corporeal, as natural philosophy shows, has matter in its nature. Matter is potency, and so is excluded from pure act. Similarly, substances as pure act cannot be the subject of any accidents. An accident by its nature is imperfect, and as subject of accidents the substance would be in potency to them. In particular, all extension is incompatible with pure act. Extension is not only an accident, but is a corporeal accident, and so is found only in bodies. Subsistent being, then, is unextended. It occupies no space. It is not in any place, in the way definite extension locates a thing. It is not in any genus or species, because these imply potency to further determination; so it has to be unique. It can have no parts, for parts are in potency with respect to the whole. All composition has to be denied it. It is absolutely simple. It is entirely immutable, for mutability means potency to become something else or to be in some other way. It is therefore not subject to motion and so is not measured by time or any other imperfect duration. It has no past nor future, but has its existence all together. Its duration is an eternal now. Such duration is called eternity.

(Owens 1963, p. 84)

Understanding potency and act as it relates to necessary being yields the interpretation offered here of the third way. It is this type of reasoning whereby one discovers all the attributes of God that follows after the five ways. Aquinas deduces these from the metaphysical insights he thinks the five ways prove.

I will make two arguments against the assertion that the third way only proves the universe and not God. First, because Plantinga never understood the metaphysics of the third way, it is difficult to see how he can know what the third way concludes to. Second, the third way demonstrates that there is one necessary being. There can only be one necessary being because of the particular metaphysical attributes that follow from the third way.15 Aquinas explains these attributes in the chapters of the Summa immediately after proving God’s existence. Among these attributes are simplicity, immateriality, and pure actuality. These attributes cannot be applied to the universe, but they can be applied to God. The universe is not simple, because it can be divided. Only a composed being can be divided, and a simple being cannot. Therefore, the universe is not a simple being. When we speak of simplicity here, it does not mean there is only one, but that it is pure act and not composed in any way. Anything that is composed or can be divided cannot be pure act or simple.

The universe is either material or immaterial. But the universe cannot be immaterial because it can be measured. Although scientists may never measure the universe, they at least think it is possible. Therefore, the universe is not immaterial. The universe is either pure actuality or it is not. It cannot be pure actuality because it is changing. Changing things are composed of act and potency, and the universe is a changing thing, therefore the universe is not pure act. This also reinforces the idea that God is eternal as a necessary being. Thus, it is wrong to say that the third way concludes to a being other than God.

5. Rebutting Possible Challenges from Plantinga

There remain three important challenges Plantinga may have for Aquinas. (1) Can Aquinas have a priority of logical necessity? (2) What is referred to when we discuss the period before possible beings exist? (3) Is there a fallacy of composition he may be committing in this argument?

For Aquinas, there is a priority of metaphysical necessity (existence), not logical necessity. Metaphysical necessity is more important than logical necessity, especially when one wants to find out about the existence of something. Logical relationships are in the mind only after a person knows about reality. The first thing that a person knows is existence (being). From understanding the ontological truth that existence is not non-existence (being is not non-being), one can derive a plethora of other truths, such as logical truths. These logical truths are based on a prior understanding of the difference between existence and non-existence. Thus, the foundation of logical truth is ontology. Furthermore, the syllogistic reasoning a person uses in order to apply logical necessity comes from an act of the mind.16 Syllogistic reasoning is first dependent upon having knowledge of a being to reason about (see Owens 1963). For example, consider: (1) All men are mortal. (2) Socrates is a man. (3) Therefore, Socrates is mortal. A person knows what is said about the being involved before considering the logical validity of the argument. Thus, the act of the intellect prior to syllogistic reasoning that knows being is more basic. Aquinas would probably say that if a person has ‘broadly logical necessity’ as the starting point of their system that they have the cart before the horse. Consequently, Aquinas would assert that Plantinga, who takes ‘broadly logical necessity’ as his starting point, has the wrong starting point.17

To the second challenge, Aquinas would respond that the possible beings that are referred to before they exist are simply referring to the divine essence. Possible beings do not exist before they are actually.18 God knows the essence of things and prior to creation essences are in his mind. In the mind of God, the divine ideas are part of the divine essence. They do not have their own act of existence and are not composed. Just as an architect has the plan of a building in his mind before the building is built, so too God has an exemplar in His mind of possible beings. Once the architect composes the parts of the building it really exists.19 In a similar way, when God composes a possible being at creation, it really exists. The possibility comes from whether or not God chooses to create the being. Thus, when referring to possibility, one speaks of whether or not God exercises divine will and power to create. If a person refers to God when speaking of this possibility, then there is no problem accounting for the referent. Therefore, there is no need to postulate possible things existing before they are actual, contra this possible challenge from Plantinga.

What can be made of the charge of a fallacy of composition? It may be asserted that even if every part of the universe is contingent, how does it follow the entire universe is contingent? This is simply a transitive property that follows. For example, suppose I told you every tile on the roof of my house is green. You’d know that my roof is green from this. In the same way, if every part of the universe is dependent, then the universe as a whole is dependent. This is especially the case when one understands the metaphysics behind the assessment as it relates to act and potency in the Thomistic framework.

6. Conclusions

In conclusion, we have exposed the background for the third way, the argument in four steps, presented Plantinga’s criticisms, answered his arguments, and have given some answers to anticipated objections. Most arguments against Aquinas’s third way come because people do not understand his metaphysics. Thus, it is plausible that Plantinga’s criticism of Aquinas’s argument is a result of his lack of understanding of Aquinas’s metaphysics, which causes him to attack a straw man rather than the third way. Therefore, the misplaced criticisms of Plantinga seem to indicate that he is just another person among the many who have not understood the third way.20