‘There can be only one’: A response to Joseph C. Schmid

Abstract

Recently, in response to an article of mine, Joseph C. Schmid has argued that some traditional theistic arguments for God's unicity are problematic in that they presuppose a controversial principle and conflict with Trinitarian theology. In this article, I answer Schmid's concerns. I defend one of the original arguments while advancing new ones, and I vindicate my abductive argument for theism over naturalism.

In previous articles . . .

Recently, I argued that theism (both in its classical and non-classical forms) enjoys an advantage over Graham Oppy's naturalism as a theory of the First Cause (Gel (2021)).¹ Given that there are several well-known arguments for the conclusion that there can be only one God, theism is able to give us an answer to how many first causes there are (one) and why (because there can be only one). Oppy's naturalism, on the contrary, leaves both questions hopelessly opened – any number of initial or fundamental physical items we were to pick (3, 44, a trillion, a morbillion . . .)² would appear arbitrary, especially given the fact that there does not seem to be a way to explain why such a number could not have been different, not even by a unit. Indeed, ‘[w]hat about the nature of initial physical items would make it impossible for there to be one more or one less than a given number N?’ (Gel (2021), 4). No answer appears to be forthcoming.

Hence, under theism the number of initial or fundamental entities is explained or made intelligible, whereas under Oppy's naturalism, as it stands, it is not. Whatever the number is, presumably it could not have been different (since, ex hypothesi, we are speaking about a necessary First Cause), but we are left wondering as to why. Theism, then, can do away with a brute fact to which, apparently, Oppy's naturalism is either committed or unable to shave off. Thus, I argued, this can be a reason to prefer theism over Oppy's naturalism, ceteris paribus. (Notice that the force of the argument relies more heavily on the ability to answer the why-part of the question.)

Joseph C. Schmid, though, begs to differ. In a recent article, Schmid (2022) has argued that this case fails on several counts, mainly because the arguments I presented for God's unicity do not work. As they stand, those arguments (i) presuppose a controversial principle, the Identity of Indiscernibles (IoI), (ii) fail to justify that there could not be any differentiating feature between two Gods and, to make things worse, (iii) actually conflict with Trinitarianism.

Schmid's response is both thoughtful and valuable – it provides opportunity for clarification and further discussion of arguments related to the gap problem, which is slowly gathering attention in the philosophy of religion. However, I don't think Schmid's criticisms succeed. In what follows I attempt to advance the debate by showing, first, that one of my original arguments, with some modifications, does work; second, that Schmid's parody argument against Trinitarianism is invalid; and third, that other arguments can be given without the above controversial principle, strengthening my case. I will also discuss the role this argument can play in the project of worldview comparison.

Defending an argument for God's unicity

God's unicity compromised? IoI

As I explained in my previous article, the classical theist's picture of God is that of a purely actual reality, something which is pure being (esse) itself. From the nature of something which was thus, I wrote, it follows it would have to be unique:

[S]uch a thing could not be multipliable, because it could not be subjected to any differentiating feature, as a genus (animal) is multiplied in its species (human) by the addition of a specific difference (rationality) or a species (human) in its individuals . . . by the addition of matter. There is nothing outside pure being that could act, with respect to it, as a differentiating feature, as the specific difference rationality is outside the genus animal or as matter is outside form, because ‘outside’ pure being there is only non-being, and non-being is nothing. So pure being could not be differentiated, as pure being, into multiple instances of itself . . . Hence, a purely actual reality that was pure being itself . . . would have to be unique. (Gel (2021), 3)³

Schmid (2022, 6) helpfully formalizes said argument thus:

1. (1) For there to be more than one thing that is pure esse, there would have to be some feature(s) that differentiate(s) each from the other(s).

2. (2) But nothing that is pure esse could have such a differentiating feature.

3. (3) So, there cannot be more than one thing that is pure esse. (1, 2)

4. (4) But whatever is purely actual is pure esse.

5. (5) So, there cannot be more than one purely actual thing. (3, 4)

Schmid's first complaint is that (1) essentially amounts to the controversial principle of the Identity of Indiscernibles (IoI), which is here just assumed without argument. IoI states that ‘if x is distinct from y, then there is some feature that one has that the other lacks’ (ibid.) – in short, that there cannot be two distinct indiscernible things. Given the controversial nature of IoI, anyone mounting an argument on it should be ready to give some argument for it – Schmid is right in pointing this out.

Now, one way to advance the discussion here would be to forget IoI altogether and put forward other arguments for God's unicity that didn't depend on it – and this I will do below. However, I don't think we need to abandon IoI that quickly. Though a full-blown defence of IoI far exceeds my purposes,⁴ I would like to briefly sketch a reason in its favour, in order to show that the above argument does not stand on intolerably unreasonable ground. And the reason is this: I think that, without IoI, our ontology runs the risk of getting chaotically overcrowded very quickly – or at least the possibility of this should force us to remain agnostic as to the number of ordinary objects we encounter in everyday experience.

For instance, I have one pencil on my desk. But if I allow it is possible that, were I to see one pencil, there are in fact two distinct indiscernible pencils, I'm not sure I can continue to be confident that there is only one pencil on my desk. Consider also that, presumably, if it is possible for there to be two distinct indiscernible objects, it is also possible for there to be three, four, ten, or a million of them. Hence, without IoI or some principle like IoI, we would constantly be in the dark as to how many objects we encounter in everyday experience.⁵

Maybe someone would argue that, even without granting IoI, the rational thing to do is to assume there is only one pencil on my desk – after all, it is rational to assume that things are as they seem to me, and it seems to me that there is only one pencil on my desk. But I don't think this objection works. For, yes, it is rational to assume thus . . . unless I have a reason to think things might not appear to me the way they are. And I think denial of IoI gives us precisely such a reason.

Consider a thought experiment. Mary is kidnapped by a mad philosopher and wakes up in a large room, chained to a wall. In front of her, she sees a nice little pine tree, and so, naturally forms the belief ‘There is a pine tree in front of me.’ But then, the kidnapper informs her that, before constructing the room, he flipped a coin to decide whether to plant one pine tree (heads) or more than one (tails) – with the condition that, were the coin to turn up tails, he would plant the additional trees so perfectly aligned behind the first one that, from Mary's perspective, nobody could tell whether there was more than one tree or not. Assuming Mary trusts her kidnapper (she knows he is a Kantian and would not lie, for instance), it seems to me that the rational thing for her to do in this situation is to remain agnostic as to how many trees there are in the room. For all she knows, there might be only one, sure, but there could also be two, three, four, etc. Mary has now a reason for not taking at face value how things appear to her.⁶

I propose that the one who denies IoI finds himself in a parallel situation. He, like Mary, has a reason for not taking at face value how things appear to him. After all, one pencil will appear to him as only one pencil – but so would two distinct indiscernible pencils (and three, four, five, etc.). As the saying goes, if it looks like a duck, swims like a duck, and quacks like a duck . . . well, without IoI, maybe it is two ducks.

One could say that we don't need the full-blown principle to avoid these (and other)⁷ undesirable consequences. Maybe it suffices to take IoI as a sort of rule-of-thumb that admits of exceptions, and to restrict these to very rare occasions. Personally, I would want to know why IoI should admit of exceptions, and why these ones and not others. It seems to me that, in the absence of a plausible story as to how contained and limited these exceptions are (and why), the previous sceptical conclusions follow – for we would be in the dark with respect to the situations in which application of IoI is warranted or not. Having said this, I am not entirely opposed to this rule-of-thumb approach. But then, I don't see either why the unicity argument would need more than a rule-of-thumb IoI. Sure, the argument would be stronger with a totally universal principle, but that a weaker one is conceded need not mean the argument is therefore without any merit. In the absence of any reason to think that beings of pure esse are not subject to IoI, the fact that no differentiating feature can be found between them should suffice to reasonably conclude that there can't be more than one.

Finally, it seems to me there is a way to tweak the above unicity argument to make it depend on a principle of identity not of indiscernibles simpliciter, but of necessary indiscernibles (that is, entities which are necessarily indiscernible, indiscernible in every possible world).⁸ This would have the advantage of being truer to premise 2, which states that there could not be any differentiating feature between beings of pure esse. If there is a possible world w where two beings of pure esse are distinguished by a differentiating feature, then one of the two is not a being of pure esse in w. Hence, beings of pure esse are indiscernible across every possible world – they are necessary indiscernibles.⁹ And while there may be some motivation to question the identity of indiscernibles, I can think of no reason to question the identity of necessary indiscernibles.

What about Schmid's objection to IoI? After suggesting that ‘the principal motivation behind IoI seems to be explicability’, for if there are no differentiating features between two distinct objects, ‘their individuation would seem to be primitive or brute’, he writes:

Why can't individuation or distinctness simply be primitive? In that case, there need not be some feature that grounds things' distinction. . . . Indeed, there seems to be a prima facie plausible argument that individuation or distinctness must ultimately be primitive. For we can equally ask: in virtue of what are those individuating features of x and y individuated? If they're not individuated by anything, then we have primitive individuation, which is precisely what IoI sought to avoid. If they have some further differentiating features, then we're off on a vicious regress. For we can further ask, of those features, in virtue of what are they individuated? And so on ad infinitum. It seems, then, that we must ultimately bottom out in primitive individuation. (Schmid (2022), 6)

It's not clear to me, though, how this objection is supposed to work. Consider two distinct physical objects, a rectangular object and a circular object. They are differentiated (among other things) by the one having the feature of being rectangular and the other that of being circular (or, if preferred, by the one being rectangular and the other not). Is there any need to appeal to something else in virtue of which the feature ‘being rectangular’ is different from the feature ‘being circular’ (or ‘not being rectangular’)? It doesn't seem so: their difference appears to be self-evident or self-explicative.¹⁰ Is this something the proponent of IoI seeks to avoid? Not really: what he seeks to avoid is diversity without discernibility. There is no indiscernibility between ‘being rectangular’ and ‘being circular’ (or ‘not being rectangular’), but there would be between two objects that shared all and only all features in common.

Additionally, even if it is true that we must accept primitive (understood in the sense of brute) individuation at some level, it doesn't follow that we need to accept it at all and any levels. In fact, we have just seen that there are compelling reasons against accepting primitive individuation for things or objects ('substances’), to which proponents of IoI usually restrict the principle.¹¹ Hence, it seems that a proponent of IoI could concede that we must ultimately bottom out in primitive individuation – only that we had better not have to do it with things or objects. And that's all the above argument for unicity needs.¹²

So, IoI, though certainly controversial and in need of a more in-depth defence, is not without warrant. Having said this, I think Schmid's points can help make the unicity argument more modest, which need not be a bad thing. Insofar as one finds IoI plausible, to that measure one has reason to think that there could only be one being of pure esse – granting that there couldn't be any differentiating feature between two hypothetic beings of pure esse, something to which I now turn.

Distinguishing beings of pure esse

We have now dealt with Schmid's criticisms of (1). But what about premise 2, that there can be no differentiating feature between two hypothetic beings of pure esse? Schmid complains that the justification given for (2) is sketchy at best, since it is unclear what ‘outside’ means in the context of the argument: ‘It certainly can't mean ‘distinct from’, since there most definitely are things distinct from pure being. But if it doesn't mean distinction, I struggle to see what it could mean’ (ibid., 7). This is fair enough,¹³ and I think a better and more straightforward justification for (2) can be given, following Edward Feser (2017, 121–122).

Under classical theism, God just is pure being itself – Aquinas's Ipsum Esse Subsistens. But if there were two Gods, two beings of pure esse, they would have to be distinguished by some differentiating feature (premise 1). However, if pure being A was distinguished from pure being B by having a feature F which B lacked, it would cease to be true that A just is pure being itself – instead, A would be being plus feature F. Add anything to A in order to distinguish it from B – A stops being something which just is pure being itself. Alternatively, being pure esse, both A and B are supposed to possess the fullness of being. But if A possesses a feature F which B lacks, then either A has the fullness of being and something else, which doesn't make sense, or B does not possess the fullness of being, in lacking F. Either way, one of the two stops being pure esse.

Consider further that feature F would have to be either an essential property of A (something which flowed from A's nature) or an accidental property A could have or not. But F could not be an essential property of A, since in such a case B would exhibit F as well. A and B, after all, are supposed to be two distinct beings with a shared nature, that of something which just is existence itself – otherwise, it is not the God of classical theism which we are multiplying. Hence, if F flowed from A's essence, it would also flow from B's essence. But neither could F be an accidental property of A, for then A would stop being something which just is existence itself, as was said above. So, nothing that was pure esse could have a feature that differentiated it from another being of pure esse. Thus, now (2) seems to be justified and we are in a better position to deal with Schmid's other objections.

Schmid's second complaint against premise 2 is that there seem to be plausible candidates for features that differentiate among beings of pure esse. He writes,

Consider, first, that most Thomistic classical theists think that being pure esse is compatible with being Trinitarian (i.e. existing as three persons). But if that's so, surely being pure esse is also compatible with being (say) Unitarian (i.e. existing as one person). It is not as though Jews and Muslims are prevented from affirming the traditional [Doctrine of Divine Simplicity] (and, with it, God's being identical to his existence) by dint of their Unitarianism. It would also seem intolerably ad hoc and inexplicable if Trinitarianism but not Unitarianism (or Binitarianism, or etc.) was compatible with God's being pure esse. If all this is correct, then we have on our hands a clear candidate for a differentiating feature among purely actual beings of pure esse: the number of persons in which they exist. In principle, one being of pure esse could be Unitarian; another could be Binitarian; still another could be Trinitarian; and so on. (Schmid (2022), 7)

Admittedly, Schmid does not claim that these are ‘genuine metaphysical possibilities’, only that ‘the argument that there cannot in principle be something that differentiates beings of pure esse fails’ (ibid.). The idea seems to be that it is the theist who has the onus to prove that the number of persons can't be a differentiating feature between beings of pure esse – say, because it is not metaphysically possible that said number be different. Until then, the number of persons could be, ‘in principle’, such a differentiating feature.

Now, this is a fair criticism given the original unclear presentation of the argument. But given how I have just defended premise 2, it should be clear what is wrong with it. For the justification offered for (2) is completely general – the point is that any feature F which pure being A had and pure being B lacked would imply that A (or B) was not, after all, a being of pure esse, contrary to hypothesis. Hence, whatever the number of persons in the Godhead is, such a feature (if we can speak this way) will have to follow necessarily from God's nature as pure esse and not be something which could vary from one being of pure esse to another. And this, after all, is what almost every classical theist participant in this debate will claim. Also, it need not be ad hoc nor inexplicable – Unitarians will typically claim that it is impossible for there to be more than one person in the Godhead (Trinitarianism being incompatible, for instance, with absolute divine simplicity); Trinitarians, that it is metaphysically necessary for God to be three persons.¹⁴ (I know of no Binitarian, or etc.). This prevents no-one (Jew, Christian, or Muslim) from affirming the key tenets of classical theism – it just means that one party in the debate is mistaken about what is or is not compatible with God's being pure esse.

Let's now address Schmid's last objection to premise 2. Schmid asks us to consider

the distinction between being identical to one's own act of existence and being identical to existence simpliciter or existence as such. Thomistic metaphysics already admits that there are (roughly speaking) different acts of existence. My act of existence, for instance, is not the same as God's act of existence . . . God, then, is identical not to the existence of you or me or trees; he is identical to his own act of existence. But in that case, it's not clear why there cannot be two things which are identical to their acts of existence. They could presumably each be identical to their own respective acts of existence, which are different from one another. (Schmid (2022), 7)¹⁵

I don't think, though, that this will work. In Thomistic metaphysics, my act of existence is different from yours (or from Fido's) because I am different from you (or from Fido). It is not, so to speak, that there is something in my act of existence that makes it different from yours or Fido's act of existence, but that our acts of existence are rendered different because they actualize something other – namely, different substances or essences (Wippel (2000), 151–152, 187–190), taking ‘essence’ technically as ‘the matter-form composite itself’ (Kerr (2015), 41).

But now take a being A whose essence is identical to its act of existence. What is the ‘content’ of A's essence? What does A's essence consist in? Simply, A's essence is to be, A's essence just is existence. What this means is that, pace Schmid, there is no real distinction between being identical to one's own act of existence and being identical to existence simpliciter or existence as such. And hence, to ask whether there could be two beings, A and B, each of which was identical to its own act of existence is not really anything different from asking whether there could be two beings, A and B, who just were existence or being itself. And we have already argued that this cannot be the case. Hence this last objection fails as well.

Trinitarian trouble?

I have now given a clearer defence of premise 2 and shown why Schmid's defeaters fail. Assuming (1) is true, does the Trinitarian need to worry? Schmid thinks yes. For anyone who accepts the above argument for God's unicity, he argues, should also accept the following parody argument against Trinitarianism (ibid.):

1. (6) For there to be more than one divine person that is pure esse, there would have to be some feature that differentiates each from the other(s).

2. (7) But nothing that is pure esse could have such a differentiating feature.

3. (8) So, there cannot be more than one divine person that is pure esse. (6, 7)

4. (9) Anything divine is pure esse. (Classical theism)

5. (10) Any divine person is divine.

6. (11) So, any divine person is pure esse. (9, 10)

7. (12) So, there cannot be more than one divine person. (8, 11)

Of course, if a sound argument for God's unicity is incompatible with Trinitarianism, so much the worse for the Trinitarian! That need not affect my overall case that theism has an advantage over Oppy's naturalism – and to be fair, Schmid is not claiming that it should. But does the Trinitarian really need to worry? I don't think so. For Schmid's parody argument, I contend, is invalid under a traditional account of the Trinity – one which Christian classical theists will often espouse. And hence, acceptance of the unicity argument does not force acceptance of Schmid's parody argument.

To see why, let's get clear on some background claims. The doctrine of the Trinity states that there is only one God who is three persons: Father, Son, and Holy Spirit. Under the traditional account of the Trinity I want to present, the three divine persons are subsistent relations within the Godhead, so that each of the persons is identical to one and the same God but really distinct from the other persons.¹⁶ The Father is God, the Son is God, the Spirit is God – but the Father is not the Son nor the Spirit, the Son is not the Father nor the Spirit and the Spirit is not the Father nor the Son. This usually invites the retort that, if each person is truly identical to one and the same God, then it follows that they should all be identical between themselves, which conflicts with Trinitarianism (see Cartwright (1987)).

One common solution to this problem that will help us advance our purposes here consists in pointing out that the objection equivocates on two distinct notions of identity – identity in being and identity in person.¹⁷ For the premises to be true to Trinitarianism, they must be understood in the first sense of identity (both the Father and the Son are identical in being to the one and only God), but for the conclusion to conflict with Trinitarianism, it must be understood in the second (the Father being the same identical person as the Son). But such a conclusion simply does not follow from the premises as understood above – all that follows from them is that the Father is identical to the Son in being, which is precisely what traditional Trinitarianism claims! The divine persons are the same one being, but they are distinct persons/subsistent relations within the same one being. In the words of Gilles Emery,

The Son is ‘an other’ (alius) from the Father, but he is not ‘something else’, and the Holy Spirit is ‘an other’ from the Father and the Son without being ‘something else’ than the Father and the Son are. . . . The alterity of the Father, the Son, and the Holy Spirit is . . . an alterity of persons based on a relation-distinction, but not an alterity of essence, nature, or substance. (Emery (2007), 133)¹⁸

Now, the Father, Son, and Spirit being identical in being, each of them simply is the one same God. How is it, then, that the three persons are distinguished from one another? By way of what's called their relations of origin – the Father is the unoriginated origin, the Son is generated from the Father, and the Spirit proceeds ('spirates’, in technical terminology) from the Father and the Son.¹⁹ And hence, ‘[e]ach [divine] person has a unique proper characteristic’ (Pawl (2020), 106) that grounds their distinction – paternity for the Father, filiation for the Son, and spiration for the Spirit. The Father is not the Son nor the Spirit, for he proceeds from no-one and is the origin of the Son and the Spirit; the Son is not the Father nor the Spirit for he is generated from the Father and contributes to the procession of the Spirit, and so on (Leftow (2004), 315; Pawl (2020), 105). Thus, the divine persons are subsistent relations in God that are distinguished because of their mutual or relative opposition – that is, because they do not relate to each other in the same way. Each one is the one God (each one has the one and only divine nature), but in a distinct relational way: the Son has the same divine nature of the Father, but in a filial way, as one who receives it from the Father; etc. (White (2022a), 445–447).

Now, what this all amounts to is to the claim that the one and only being or substance which is God admits of ad intra differentiation or distinction by way of internal immanent processions – that the one and only divine nature subsists in three personal modes which are relationally distinct according to an order of derivation (White (2022a), 409–424). And this is what will allow us to see the equivocation in Schmid's parody argument. For now we can distinguish, for lack of a better terminology, between ad intra differentiation and ad extra differentiation.²⁰ While the argument for God's unicity denies the possibility of any ad extra differentiating feature between two distinct beings of pure esse, it remains silent about the possibility of ad intra differentiation between subsistent relations or persons within the same one being of pure esse. For all the argument is committed to, this may or may not be possible. So, with this in mind, let's recover the first half of Schmid's parody argument:

(6) For there to be more than one divine person that is pure esse, there would have to be some feature that differentiates each from the other(s).

(7) But nothing that is pure esse could have such a differentiating feature.

(8) So, there cannot be more than one divine person that is pure esse.

Now, the conclusion is somewhat ambiguous and admits of two possible readings. For (8) to really conflict with Trinitarianism, it must be interpreted as

(8a) There cannot be more than one divine person that is the same one being of pure esse.

If, instead, we were to interpret it as

(8b) There cannot be more than one divine person that is, each, a different being of pure esse,

this will certainly make Tritheists object, but no traditional Trinitarian will complain. So, for this really to constitute an argument against Trinitarianism, (6) and (7) must establish (8a). But the same ambiguity is present in the way Schmid phrases the premises. For, again, (6) can be understood either as

(6a) For there to be more than one divine person that is the same one being of pure esse, there would have to be some feature that differentiates each from the other(s),

in which case it will be true for the Trinitarian (understanding the idea of a differentiating feature in a broad enough sense), for it refers to the ad intra differentiation that takes place within the Godhead, due to the distinct relations of origin between the divine persons.²¹ Or we can understand (6) as

(6b) For there to be more than one divine person that is, each, a different being of pure esse, there would have to be some feature that differentiates each from the other(s),

in which case it is also true, but not what the traditional Trinitarian has in mind when saying that there is a Trinity of divine persons. Likewise, (7) can be understood either as

(7a) Nothing that is a being of pure esse can have a feature that distinguished it from another that was the same one being of pure esse (for short: Nothing that is pure esse can admit of ad intra differentiation),

in which case such a premise is nowhere to be found in the unicity argument, explicit or implicit. Or we can understand (7) as

(7b) Nothing that is a being of pure esse can have a feature that distinguished it from another being of pure esse (for short: Nothing that is pure esse can admit of ad extra differentiation),

in which case it is true and part of the unicity argument. But then, we find that there is in Schmid's argument an equivocation that makes the inference to (8a) invalid – an equivocation, precisely, between the ad intra differentiation of the persons within the same one being of pure esse and the ad extra differentiation between two hypothetical beings of pure esse. For (6) to be true to Trinitarianism, it must be understood in the sense of ad intra differentiation, as (6a) – but for (7) to be true to the unicity argument, it must be understood in the sense of ad extra differentiation, as (7b). Hence, if we are speaking of ad intra differentiation, then (6) is true but (7) is false or unjustified, and (8a) does not follow.²² And if we are speaking of ad extra differentiation, both (6) and (7) are true, but (8a) still does not follow – what follows is (8b), something which no traditional Trinitarian denies.

At this point, could someone claim the problem to be that any justification for (7b) will inevitably carry over to (7a), creating a bridge between the unicity argument and the parody argument? Might one say, for instance, that if the Son has his proper characteristic (filiation) in distinction to the Father, then the Son can't be the same being of pure esse as the Father, but being plus filiation? Not really, not without misconstruing traditional Trinitarianism altogether. For the idea is that each person's proper characteristic is not something extra that gets ‘added on’ to the person or to the divine nature, like an accident to a substance. Given divine simplicity, there are no accidents in God and everything that is in God is God's own substance. And so, the persons are relative in all that they are, that is, the Father just is his paternity, the Son just is his filiation, and paternity and filiation just are, in turn, the one divine nature, despite being relationally distinct from one another (White (2022a), 431–434 and 448–449).²³ Thus, the argument for unicity defended above is not incompatible with a traditional account of the Trinity. Traditional Trinitarians need not worry about Schmid's parody argument.

More arguments for God's unicity but no more ‘IoI-ing’

I have now defended one of the unicity arguments from Schmid's objections. However, the controversial nature of IoI haunts it, and so it would be nice to my overall case if there were other arguments for God's unicity that did not depend upon IoI and that could appeal to someone who denied it. Are there any such arguments? I will explore two.²⁴

From simplicity to unicity

In Summa Theologiae, I, q. 11, a. 3, Aquinas gives three arguments to the effect that God is one. Our interest here is in the first one, an argument from simplicity. According to classical theism, God is absolutely simple, composed of no parts whatsoever. There is in God no composition of essence and existence, form and matter, substance and accidents and, for our purposes now, nature and subject, essence and individual. This means that God is identical to his Deity – or as Schmid himself puts it, ‘God is God's essence’ (Schmid (2022), 1). But then, reasons Aquinas, there can be only one God. Why? Because, in God, that which makes him God is identical to that which makes him this God. Deity, then, can't be shared between multiple individuals, as humanity can – whatever is God (whatever has Deity) will, by that same token, be this God, the same one God.²⁵

Consider for comparison that if Socrates was identical to humanity, there could only be one human being – Socrates. If Socrates is identical to humanity and Plato is not the same being as Socrates, then it follows that Plato can't be human. Likewise, if this God is identical to Deity and X is not the same being as this God, it also follows that X can't be divine.²⁶ Again, given divine simplicity, only that which is identical to this God can be divine. In other words, Deity is hacceity, and hence, when it comes to God, ‘There can be only one.’

Note how this argument does not depend on the truth of IoI. Even if there could be, in general, two distinct indiscernible objects, the point is that, in God's case, we could be certain that such a thing could not take place. There could not be two distinct indiscernible Gods, nor two distinct discernible ones, because given divine simplicity Deity is not an essence that can be shared by multiple individual substances. Hence, whatever is distinct from this God will be anything except another God.

From perfection to unicity

The second argument follows Brian Leftow (2012) and goes from perfection to unicity. In doing so it will have the advantage of being neutral between classical and non-classical theism.²⁷ The crux of the argument is that, plausibly, unicity is a perfection, or else follows from something which, also plausibly, is a perfection. And so, a perfect being (God) would have to be unique. Apart from direct intuition that unicity is a perfection, there are several indirect paths we could take to arrive at the same conclusion.

First, consider that F is a perfection if it is ‘objectively and intrinsically such that something F is more worthy of respect, admiration, honor, or awe than something not F, ceteris paribus’ (Leftow (2012), 178). But it seems that something unique is more worthy of respect, admiration, honour, or awe than something not unique. Hence, being unique seems to be a perfection. But there does not appear to be any incompatibility with being unique and other properties a perfect being ought to have. Hence, we can say that, plausibly, a perfect being would be unique.

Consider now that a perfect being would plausibly possess supreme or absolute value. But something is more valuable in the same measure as it is more unique – or at least that seems reasonable enough and congruent with how we measure value. Hence, a perfect being would plausibly be unique.

Consider also that it seems to follow from the notion of a perfect being that it could not have a superior, that nothing could be greater in perfection than it. But there is also a case to be made that ‘there cannot be something wholly distinct from [God] and as great as He is’ (ibid., 207) – that is, that a perfect being could not have an equal. Indeed, it seems greater to be unmatched in perfection than not to be. As Leftow puts it, ‘[i]t would be greater to be intrinsically such as to be the greatest possible being among commensurable rivals than not to be. No constellation of attributes could confer more perfection than one that made one thus greatest’ (ibid.). Hence, it seems to follow once more that a perfect being would plausibly be unique – it would have no superior and no equal.

Finally, consider what Leftow calls the GSA-property (short for ‘God, Source of All’): x has the GSA-property if, for any concrete substance wholly distinct from x, x and only x makes ‘the creating-ex-nihilo sort of causal contribution’ to its continued existence (ibid., 21). As Leftow argues, the GSA-property is either a perfection or a constituent of other perfections. Why think this? First, consider that ‘[b]eing a potential ultimate source of some proportion of what benefits things is a good property to have’ (ibid., 22). But being the ultimate source of all that benefits things would be the maximal degree of this good property, and hence, given that ‘a property is a perfection iff it is the maximal degree of a degreed good attribute to have’ (ibid.), being the ultimate source of all that benefits things is a perfection. Now, such a perfection supervenes on the GSA-property – and so, either the GSA-property, by a plausible supervenience principle, is itself a perfection or it is a necessary condition of a perfection. In either case, a perfect-being will have the GSA-property.

Consider also that the GSA-property, together with the ability to freely exercise one's own power, constitutes the property of having complete control over all other concrete objects. But ‘[i]t is good to have power over other things’ existence . . . Power over existence is degreed. Complete power over all other concrete things' existence is its maximum, and so plausibly a perfection’ (ibid.). In this case, the GSA-property is a constituent of another perfection, and so a perfect being would have the GSA-property.

But it seems clear that there could only be one being which had the GSA-property. For suppose there are two distinct gods, Alpha and Omega, which both have the GSA-property. Because of that, Alpha and Omega would simultaneously be causally dependent on each other, which is viciously circular – Alpha will be creating Omega only insofar as Omega will be creating Alpha, but Omega will be creating Alpha only insofar as Alpha will be creating Omega. So, at most only one thing can have the GSA-property (ibid., 192–193). But if a perfect being would plausibly have the GSA-property, it follows that there could only be one perfect being.

Again, none of these arguments from perfection to unicity relies on IoI. Even if IoI is false and we can have two distinct indiscernible beings, we still could not have two distinct perfect beings, indiscernible or not, for the reasons given. Sure, the arguments are far from being apodictic proofs. As Leftow himself acknowledges (ibid. 12), perfect-being arguments rely on intuitions about perfections, and our intuitions are fallible. Because of this I have explored several routes to support the same conclusion (and maybe more could be added), so that the argument has more force. Even so, modesty in argumentation need not be a bad thing. Insofar as someone finds these intuitions plausible, to that measure he has reason to think that there could not be more than one perfect being.

Does this reasoning conflict with Trinitarianism? If unicity is a perfection that any perfect being ought to have, some will say, then for a divine person to really be divine (and hence, perfect) it would also have to be unique. And so, the same intuitions would support the conclusion that there can only be one divine person. But at least the traditional account of the Trinity presented above can easily deal with this objection. The ad intra differentiation that takes place within God does not make it so that now we have more than one perfect being, and each divine person is still perfect in being identical to one and the same perfect substance, God. Also, further considerations about perfection could support the case that the one and only perfect being should be, internally speaking, more than one person (see, again, Sijuwade (2021)).

Can these arguments be of use to the naturalist?

Let's recapitulate. In my original article I argued that theism has an advantage over Oppy's naturalism as a theory of the First Cause because theism can answer how many first causes or fundamental entities there are and why. This throws additional light onto the First Cause, shaving off one brute fact to which Oppy's naturalism, as it stands, seems committed or unable to eliminate. Adopting the theist's hypothesis for a First Cause, we get to understand something that, adopting Oppy's, seems condemned to remain unintelligible. And this, ceteris paribus, is a point in favour of theism vis-à-vis Oppy's naturalism.

I have now defended one of my original arguments from Schmid's objections and put forward two more that do not depend on the controversial IoI. It seems to me, then, that the whole case is strengthened and poses a challenge to the naturalist. Can the naturalist appropriate the theist's unicity arguments and adapt them to a naturalistic First Cause? I briefly considered this question in my previous article (Gel (2021), 6 and 8), but it is worth pondering it once more.

I think the answer is clearly ‘No’ with respect to the arguments that go from perfection to unicity. Surely, to accept that the First Cause is a perfect being would be to abandon naturalism, at least in any relevant sense of the word. Could the naturalist borrow from the other arguments, and say, for instance, that the First Cause is absolutely simple, purely actual, or pure esse but still a natural reality? Here, I want to say that it depends – it depends on whether the rest of the divine attributes follow from the nature of something which was so. Classical theists, old and new, typically claim that they do.²⁸ However, further discussion is needed, given that 2nd-stage arguments (as they are sometimes called) tend to be ignored by those who do not concede the 1st-stage ones.

Anyhow, I want to address some remarks of Schmid that are relevant here. In his article, Schmid takes issue with my suggestion that a purely actual reality would have to be immaterial. Schmid claims that it is not at all clear that every material thing is both mutable and potential in many ways. He writes:

Consider atemporal wavefunction monism. According to this view, there exists a fundamental, physical, non-spatiotemporal entity: the universal wavefunction. This is a perfectly respectable view that has seen a blossoming of interest in philosophy of physics. If we understand ‘material’ and ‘physical’ to be synonymous, then it simply follows that there are perfectly respectable views on which there is a fundamental or foundational, unchangeable, timeless, material thing. We can also suppose that (a) the fundamental layer of reality is necessary (as Gel himself supposes in his second argumentative path) and (b) the fundamental layer of reality is cross-world invariant. From all of this it simply follows that the fundamental atemporal wavefunction has no potencies for change, cross-world variance, or non-existence. We therefore seem to have a perfectly respectable naturalist view on which the foundation of reality is a material, unchangeable, purely actual thing. (Schmid (2022), 9–10)

Surely, atemporal wavefunction monism is an interesting view in its own right. Still, as a hypothetical example of a purely actual material thing, in the Aristotelian-Thomistic sense of ‘material’ with which I was operating, it is bound to be incoherent. For a material thing, in Aristotelian-Thomistic philosophy, is that which has matter, and matter is that which persists through substantial change and is thus characterized as pure potentiality to receive any form (Feser (2019), 28–29). A purely actual material thing, then, in this sense of ‘material’, makes no sense – it would have to be something which lacked all potentiality and still was potential in some way.

Schmid's point here turns on the key phrase ‘If we understand “material” and “physical” to be synonymous’, but if this move allows for there to be a purely actual material thing, then Schmid needs to tell us what ‘physical’ means in this context and how it is opposed to ‘immaterial’ in the Aristotelian sense. For if it is not so opposed, we would simply be changing the subject, not speaking of material in the Aristotelian sense, but in another sense, material*. But then, a purely actual thing could both be necessarily immaterial in the Aristotelian sense and maybe also material in the material* sense. That does nothing to invalidate the classical theist's inference to the immateriality of the First Cause – it is no more proof that there could be a purely actual material thing than saying that if we understand ‘round’ as synonymous with ‘red’, then there could be a round square.

Is this advantage worth the price?

Schmid argues repeatedly in his article that, even if classical theism has a simpler account of the First Cause than naturalism, naturalism is simpler tout court, when both are compared as overall theories, and that it is this that should primarily concern us when assessing theories according to their simplicity (Schmid (2022), 4).

I have my doubts that this is entirely correct, but let's concede it for the sake of argument.²⁹ Let's assume also that I am right and there are sound unicity arguments such as those I have defended. Now, is the theoretical advantage of theism identified here worth the price of theism's added complexity? It is not easy to say – there is no straightforward equation when comparing gains in explanation and costs in simplicity. But it is important to remember that the advantage we have been discussing can be taken as ‘an additional or supplementary reason to be weighted jointly with any other available evidence’ (Gel (2021), 8). Maybe this advantage, on its own, does little to tip the scales in favour of theism, but it can still play an interesting role in a more overarching cumulative case that ends up doing just that.

Consider, for instance, that perfect-being theism can explain all or mostly all properties ascribed to God by appealing to just one basic property – perfection. If the traditional arguments for deducing the divine attributes are correct, classical theism can do so too. But there is nothing comparable in naturalism, and no expectation that there will be (Leftow (2017), 330–332). That a being is perfect, or purely actual, or pure esse, also seems to make sense of why it is necessary (see, for instance, Byerly (2019)). But in naturalism, and especially in Oppy's naturalism, the fundamental natural entities are necessary and that's it, full-stop (see Oppy and Pearce (2022), 113). Putting all of this together, it seems that theism could have the tools to explain the number of what is most fundamental, its nature and its necessity – and so, less and less is brute at the fundamental level in theism. Someone could add considerations from fine-tuning, beauty, and other arguments and the scales may begin to tip for him as more and more advantages in explanation are gained for the same price of some extra-ontology. And that seems to me a pretty good deal.

In conclusion

In my previous article, I argued that theism has an advantage over Oppy's naturalism in that theism can answer the double question of how many first causes there are and why, while Oppy's naturalism seems lost on both fronts. In this article, I have defended one of my original arguments for God's unicity from Schmid's objections and offered two more that don't rely on the controversial IoI principle, thereby strengthening my overall case. In addition, I have discussed whether the naturalist could appropriate the theist's first cause while remaining a naturalist and concluded that the prospects of such a move appear slim, though more work needs to be done on this front. Finally, I have considered the role this argument can play in a more overarching cumulative case for theism.

While I have been critical of Schmid's arguments, I think he provided an engaging response and much needed push-back. His objections have allowed us to go a step further than before – clarifying one of my original arguments, showing how it is no threat to the Trinitarian, and exploring additional arguments for God's unicity. If this article advances the discussion in any degree, as I hope it does, it is indeed to Schmid's credit.