The functional mind and the trinitarian God

Abstract

Within the space of monotheistic options, trinitarian monotheism holds a puzzling place. It asserts that God is a single being who is, somehow, also three distinct persons. This form of monotheism has regularly been charged with being either inconsistent, unintelligible, or undermotivated – and possibly all three. While recent explorations of trinitarian monotheism have tended to rely on work in metaphysics, this paper turns to the philosophy of mind, showing that functionalist theories of mind prove to be surprisingly hospitable to trinitarian monotheism. This paper will address only the inconsistency and unintelligibility objections, showing that if role-functionalism (or something near enough) is both consistent and conceivable, then it is both consistent and conceivable that: God is a single being who is exactly three distinct persons because there is one primary divine person who interacts with exactly one system-sharing re-realisation of his own person-type.

Introduction

Monotheism, for present purposes, is the view that there exists just one personal being whose knowledge, power, and rationality are jointly maximal. Monotheists reserve the name ‘God’ for this personal being.¹ Trinitarian monotheism is a version of monotheism that says God is not merely a personal being, but God is a tripersonal being, that is, God is three distinct persons. This form of monotheism has regularly been charged with being either inconsistent, unintelligible, or philosophically undermotivated – and possibly all three.² Call this the trinitarian trilemma.

A prominent response to this trilemma among philosophers has involved the development of models of the trinitarian God that borrow from established work in metaphysics. The body of work drawn upon has involved ideas about relative identity, time travel, hylomorphic compounds, spatially extended simples, qua objects, persisting fissioned individuals, and other metaphysical marvels.³ The aim of these forays into metaphysics is to discover a consistency proof (or proof sketch) that can also help blunt the force of the unintelligibility charge. In contrast, however, some have sought to blunt the force of the unintelligibility charge by, surprisingly, endorsing the inconsistency charge. This approach has involved the exposition of non-classical logics on which we can understand (or at least better understand) metaphysical structures that involve true contradictions.⁴ But when it comes to the undermotivation objection, philosophical defences of trinitarianism are largely silent. This is because most philosophers of religion appear to hold that the primary evidence for a tripersonal view of God, if there is any, comes from theological sources (creeds, scriptures, traditions) rather than from a priori insight.⁵

The approach to the trinitarian trilemma to follow is unlike these. Instead of turning to recent work in metaphysics, it turns to recent work in the philosophy of mind. In particular, it turns to the widely endorsed role-functionalist theory of mind to demonstrate the following:

Weak Functionalist Trinitarianism: If role-functionalism is both consistent and conceivable, then it is both consistent and conceivable that God is a single being who is exactly three distinct persons because there is one primary divine person who interacts with exactly one system-sharing re-realisation of his own person-type.⁶

The first section outlines the standard role-functionalist account of mental states, minds, and persons. On this view, mental state-types, mind-types, and person-types are functional kinds and these are realised in systems whenever a system has (instantiates) the relevant function. Systems with mental states can be made up of any kind of substances (material or immaterial) provided the substance in question instantiates the relevant function.⁷ While this paper relies on standard role-functionalism, its main conclusions can also be reached from non-reductionist and anti-physicalist variations on role-functionalism (noted below). Further, while this paper is anchored in role-functionalism, certain other forms of functionalism will likewise support the same kinds of claims about the trinity, for example, realiser-functionalism. Henceforth, ‘functionalism’ should be taken to refer only to role-functionalism.⁸

The next section develops a functionalist account of the second person of the trinity. Functionalism entails personal beings, including God, are systems that realise the structured network of functional roles that individuate person-types. This opens up what functionalists should view as a consistent and conceivable possibility: God has a constituent person – call him God¹ – who intentionally brings forth a maximally accurate, system-sharing, re-realisation of his own person-type. It will be argued that God¹, under certain assumptions, would have this ability and that this way of re-realising God¹’s person-type in the same system would yield a second token divine person who is ‘of the same substance’ with God¹. We’ll call this second divine person God².

The following section leverages a widely acknowledged entailment of functionalism: the interaction of token persons can itself realise further person-kinds. This entails that: if God¹ and God² jointly interact in ways that realise the network of functional roles associated with God¹’s person-type, then another token-distinct person will result. Assuming all of God¹’s and God²’s interactions are intra-system interactions, this third system-sharing, re-realisation of God¹’s person-type – call him God³ – will be ‘of one substance’ with God¹ and God². A distinctive feature of this approach to the trinity is that it entails that God is not only one tripersonal being, but that each token person is a realisation of one type of divine person.

The final section ends with a discussion of whether functionalist trinitarianism is compatible with God having a simple substance.

Weak functionalist trinitarianism I: towards the second person

What could God¹ do in order to generate a second divine person without generating a second substance? Functionalism entails an answer: God¹ could bring about a second realisation of his person-type in the same substance that serves as his realising system. We will quickly describe the typical functionalist view of mental states, minds, and personhood as well as a couple variations on functionalism that trinitarians can, if they wish, take advantage of: non-reductive functionalism and anti-physicalist functionalism. Next we will explain how and why functionalism entails that God¹ can generate a second divine realisation of his own person-type without generating a second substance.

Functionalist theories of mind

Functionalism is a, if not the, leading approach to the metaphysics of mind in contemporary philosophy.⁹ Functionalism is often introduced with obvious functional kinds: barriers, vehicles, traps, pumps, locks, calculators, leaders, law enforcement officers, and so on. These are defined not in terms of the stuff they are made of (silver, steel, plastic, silicon, grey matter, human bodies, souls, or some combination thereof), but in terms of the functional role they fulfil in a system. The kind of stuff that instances of them are made of only matters insofar as that kind of stuff is required to fulfil a given role in a system.

Let’s walk through, at a rather high level, how functionalists think of particular mental states before mentioning their view of minds and persons. Take Socrates’s belief that it is raining. Beliefs are a functional kind, a kind whose essential characteristics involve: specific ways of interacting with evidential inputs (e.g., perceiving rain, hearing weather reports, feeling raindrops); specific ways of interacting with other mental states (e.g., the desire not to get wet); specific ways of contributing to the formation of intentions (e.g., intending to take an umbrella or remain indoors); and a tendency to produce corresponding behaviours under certain conditions (e.g., retrieving an umbrella or choosing not to go outside). These ‘specific ways of interacting’ are to be specified largely in terms of counterfactual dependence relations. So a belief that it is raining is a type of mental state that is to be identified with that type of functional role, while Socrates’s token belief is the realisation of that functional role in Socrates. The realisation of mental states in Socrates happens in virtue of Socrates instantiating a lower-level or ‘base’ property (e.g., having a certain neuronal arrangement) that has the functional role of the mental state in question.¹⁰

A distinctive characteristic of functionalism is the multiple realisability of mental states: the kind of substance that makes up a system (biological, artificial, immaterial souls) does not matter so long as the system can instantiate the lower-level properties that realise mental states. Accordingly, functionalism implies that mental states can be not only realised in Socrates, but also re-realised in Socrates. Take a case of redundant memory storage. All that is needed for a re-realisation of a memory to occur in Socrates is for Socrates to twice instantiate the lower-level property that realised that memory to begin with, or for Socrates to instantiate a different lower-level property that realises that memory’s characteristic functional profile. Hence multiple realisability can occur within single individuals as well as across distinct individuals.

So functionalism treats mental state types as abstract role types, and it treats concrete individuals with minds as systems that instantiate token mental states in virtue of instantiating lower-level realisers, for example certain neuronal arrangements. So any system that instantiates mental states has a mind in at least a minimal sense. Like mental state types, mind-types are individuated by functional organisation: structured networks of functional roles. A collection of token states m₁…m_n (e.g., beliefs, desires, intentions, etc.) belongs to one mind just when m₁…m_n stand in the right pattern of mutual dependence (counterfactual/control) relations that integrate belief, desire, intention, etc. A single system can instantiate many mental state tokens without those tokens all being part of one mind. Functionalists can say, for example, that this is what separates the beliefs of Jekyll from those of Hyde. Jekyll and Hyde may be distinct minds instantiated in a single system (e.g., one brain) owing to a lack of functional integration among their mental states.

What is the relation between systems and substances (i.e., the bearers of properties)? The individual substance(s) that yield a mind (i.e., a mental state instantiating system) can in principle be a collection of distinct substances, a single mereologically composite substance, or a single mereologically non-composite (simple) substance. All that matters is that the substance(s) in question instantiate the lower-level properties that realise the relevant functional roles.¹¹

Minds may fail to be persons. Newborn lambs realise mental states given that they see, hear, and respond to things in their environment. But they fall short of the robust kind of personhood that is characteristic of mature human beings and divine persons. While characterisations of this sort of personhood can differ, such persons are widely taken to be minds that are conscious, self-conscious, and have rational capacities.¹² The relevant rational capacities are generally treated as a matter of having a constellation of functionally characterisable abilities involving reasons.¹³ As such persons are conscious, self-conscious, and rational beings, they are not abstract types that can be multiply realised. But mind-types and person-types are abstract kinds and these are multiply realisable. Were God to have cloned Adam rather than making Eve, he would have brought about two realisations of the person-type of Adam. There would then have been two token persons, but only one person-type.

Not all who are sympathetic to the functionalist account of mental states, minds, and persons embrace it without qualification. For example, Chalmers (1996, 247–249) has argued for non-reductive functionalism on which only non-phenomenal mental states can be identified with functional states, while phenomenal/conscious mental states are to be seen as systematically correlated with functional mental states. Alternatively, some might wish to maintain that the functionalist framework that fits best with traditional monotheism is one that adds the constraint that only immaterial substances (souls) are capable of realising the functional organisations sufficient for genuine mental states. This would be an anti-physicalist functionalism. Importantly, the view of the trinity to emerge below is consistent with these deviations from standard functionalism, and for expressive convenience we will limit our attention to standard functionalism.

From functionalism to the second person of the trinity

The idea that God¹ could cause or bring about a distinct co-equal person is not new to philosophical theology. Following Augustine (2012) and Richard of St. Victor (1958), Swinburne (2018, 429) takes this to be a straightforward implication of God¹ having maximal power. But we do not want to take this for granted without discussion. For we want to establish the claim that a being like God¹ would have what it takes to bring about the re-realisation of his own person-type in his own system.

According to traditional monotheistic views, God¹ has maximal knowledge. This includes both propositional knowledge (knowledge of truths) as well as practical knowledge (knowledge of how to do things). Now, God’s propositional knowledge extends to God¹ himself, that is, God¹ knows all the truths it is broadly logically possible for him to know about himself.¹⁴ Now, standard views of propositional knowledge entail that persons have propositional knowledge because they have certain representational mental states (e.g., beliefs).¹⁵ Assuming the same is true of God¹’s propositional knowledge, God¹’s propositional self-knowledge is constituted by a collection of self-representational mental states.

It is implausible to maintain that the collection of God¹’s self-representational mental states themselves realise the functional role persons.¹⁶ But, according to functionalism, God¹’s propositional self-knowledge and practical knowledge give him an opportunity. For God¹ is a person who is himself realised in a particular system (presumably an immaterial substance). And God¹’s knowledge will not only include facts about his mental states, it will also include knowledge of facts about how his mental states are realised in his system as well as knowledge how to bring about realisations of minds like his own within systems like his own. To assume otherwise would be to assume that God¹’s propositional and practical knowledge is not maximal.

Knowing all the facts about how a mind is related to its system as well as knowing how to bring about a realisation of a mind in a system is not generally enough to ensure that one has the ability or power to do so.¹⁷ For example, when we are considering the possibility of realising two minds within a single existing system, the issue becomes one of the capacity of the system in question. Some might worry, then, that God¹’s system is already ‘maxed out’ by God¹ himself and thus is not capable of enabling a re-realisation of God¹’s person-type. This is a worry that has bite with finite systems: for if the capacities of your system have an upper bound, it may not be possible for it to enable a re-realisation of your person-type.

But this worry gains less traction in the case of infinite systems, that is, systems that have the capacity to realise infinitely many states and dependence relations among those states. That is, assume the number of states and dependency relations among the states capable of being realised in God’s system is some order of infinity ℵ_n. Any system capable of realising ℵ_n-many states and dependency relations has the capacity to host 2 ✕ ℵ_n such states and dependency relations. This is an entailment of the mathematically trivial result that for any natural number к and any infinite quantity ℵ_n: к ✕ ℵ_n = ℵ_n.¹⁸ Since the natural numbers are countably infinite, you can select any arbitrarily large finite number к within the natural numbers and the result of multiplying it by ℵ_n will remain ℵ_n. Thus, for any natural number к, if God¹ is realised in an infinite system, then God¹’s system has the capacity to host к-many more realisations of God¹’s person-type.¹⁹ We will assume in what follows that God¹’s maximal knowledge and power require that God¹’s person-type be realised in an infinite system in the sense noted above. Within the space of monotheistic views, it is not unusual to maintain that God is infinite in various senses. What is unusual is the way it is being recast in functionalist terms: a mind with infinite capacity requires the system that instantiates it to have infinite capacity.

Take the following collection of claims:

The Maximality Package. God¹ is maximally powerful. God¹ has maximal propositional and practical knowledge. God¹ is himself instantiated in an infinite system (because that system hosts a realisation of his person-type).

The Maximality Package appears to entail the following:

The Power of Perfect Self-Re-Realisation (PPSR). God¹ has the power and knowledge to bring about a re-realisation of his own person-type in his own system in a way that is maximally accurate.

If God¹ has this power, then the result of God¹ exercising such power would be a token-distinct person according to functionalism. Again, let’s refer to this prospective second token instance of God¹’s person-type as God².

For the Maximality Package to fail to entail PPSR, it would have to be the case that God¹’s power, knowledge, or system could be limited in some way that either (i) prevented any additional realisation of his person-type, or (ii) prevented a re-realisation of his person-type that is maximally accurate. Standard views about God¹’s extremely high degree of knowledge and power will not support blocking the entailment at (i). But blocking the entailment at (ii) requires an unintended reading of ‘maximal accuracy’. So we’ll now say a couple of words about that.

To claim that God² is a maximally accurate re-realisation of God¹ is not to claim that they share all their intrinsic features. For God¹’s maximal power and self-knowledge can only ensure that there are no avoidable differences between God¹ and God². But some differences cannot be avoided. For example, if God² is to have maximal knowledge he should believe no falsehoods. Thus, he should not, for example, believe that he is numerically identical to God¹ even though God¹ will believe that he is identical to God¹. In general, God² should not believe falsehoods about who he is, who God¹ is, and what relations they stand in to each other. All of this logically requires that God¹ and God² have some distinct mental states.²⁰ This is all consistent with the intended reading of ‘maximal accuracy’.

Now, if God¹ re-realises his own person-type in his own system in a way that’s maximally accurate, then God²’s powers cannot fail to be as expansive as his own. For functionalism seems to imply that God¹ has the powers that he has because of the kind of person that he is and because of the kind of system his mind is realised in. Since God² is a maximally accurate re-realisation of God¹ in the same system, it follows that God² and God¹ should share the same powers.

For that same reason, God¹ and God² will be alike in their power to freely act and this will bring about further unavoidable differences between God¹ and God². For if God² is a maximally accurate re-realisation of God¹, and God¹’s power to act freely is a product of God¹ being the kind of person that he is, then God² must enjoy the same degree of freedom that God¹ does. Thus, when it comes to purely discretionary actions (free actions that are not required by God¹’s nature) God¹ and God² might make different choices or have (or develop) different preferences. So in addition to having some distinct beliefs, God¹ and God² may well develop distinct preference states. Again, all of this is consistent with the intended reading of ‘maximal accuracy’.

Let’s quickly summarise where we’re at. This section has argued that if functionalism is true, then all persons exist in virtue of systems having lower-level properties that realise the functional profile of a person-type. The same is true of God¹. And since he is a person of maximal power and maximal (propositional and practical) knowledge in an infinite system, God¹ has the capacity to bring about a second, maximally accurate realisation of his own person-type in his own system.

Weak functionalist trinitarianism II: towards the third person

The consistency and conceivability of trinitarian monotheism could be defended by arguing that God¹ could bring about a second re-realisation of himself. But this will not be the defence given here. Rather, it will be argued that the trinitarian can exploit a widely recognised entailment of functionalism: that the interaction between persons can itself realise a further person. In the trinitarian tradition this general idea is not new. Friedman (2010) traces a tradition in Christian thought stemming from Augustine (cf. De Trin. XV.15.29, XV.6.10) through the Franciscan tradition where the Holy Spirit is a further distinct divine person who emanates from the voluntary love shared between the Father and the Son. This is also the view of Jonathan Edwards (2008 [1740], 121–141).

Of course, it is a familiar idea that two things of the same kind can be related in a way that forms a third instance of the same kind. Two rectangles may form a further rectangle. However, the idea that persons could interact in ways that form further persons is not transparently true. This somewhat surprising entailment of functionalism has been widely discussed in relation to Ned Block’s (1978) ‘China Brain’ thought experiment. The next section presents Block’s thought experiment and Chalmers’s (1996) functionalist response, both of which are instructive. With that as background, it will be argued that if functionalism is consistent and conceivable, then it is consistent and conceivable that God¹ and God² host the kind of interpersonal interactions needed to jointly bring about a further re-realisation of God¹’s person-type.

Collective person realism

Can a collection of distinct persons interact in ways that yield a further distinct person? For present purposes, answering this question in perfect generality is irrelevant. What is relevant is what follows from functionalism. That is, what we are concerned with is whether the following conditional is true:

Collective Person Realism (CPR). If functionalism is true, then a new individual person results whenever a collection of distinct individual persons jointly engage each other in ways that realise the function of an individual person.

The qualification ‘individual’ is meant to highlight an unintended reading of CPR on which performative (/group, /collective) persons are said to exist in virtue of the activities of individual persons. Corporations, administrations, school boards, and the like are examples of performative persons, each of which exists in virtue of the activities of their individual members.²¹

But performative persons cannot easily rescue trinitarians from their trilemma for two reasons. First, it’s not clear that performative persons, in their familiar manifestations, have all the essential properties of individual persons. Corporations, administrations, school boards, and the like are not plausibly regarded as conscious and self-conscious. So they are not ‘persons’ in the way required for trinitarianism. Second, for most trinitarians, all members of the trinity are supposed to be persons in the same sense of ‘person’. So even though one could argue for a non-standard version of trinitarianism on which the third person of the trinity is merely a non-conscious performative person, this would be attractive to very few trinitarians.

Now, CPR is true. Functionalists and anti-functionalists have noted this. To appreciate this it helps to consider Ned Block’s (1978) ‘China Brain’ thought experiment, which involves a case like this:

Socially Realised Brain. Take an arbitrary adult human being S¹ at some time interval t ₁-t_n. It is possible that there exists an individual person S² who has the same kinds of internal psychological and experiential states as S¹ at the time interval t ₁-t_n because the Chinese nation brings about a realisation of the very same kind of total functional organisation that S¹’s brain had during the time interval t ₁-t_n. The Chinese nation does this by having all its citizens interact with hand-held radios in ways that accurately mirror the activity of S¹’s neurons during the time interval t ₁-t_n.

This kind of case was issued as an objection to functionalism: a functional organisation involving lots of individual people with hand-held radios seems incapable of yielding a mind that has conscious experiences, for example experiences of pain, pleasure, colour, hope, desire, and the like.

But in defence of functionalism, Chalmers (1996) has argued that cases like the Socially Realised Brain are highly under-described, representing only a caricature of the functionalist’s position. Indeed, when cases like the Socially Realised Brain are resolved into detail sufficient to accurately represent the functionalist view, the intuition that a nation of people cannot realise the same kind of mind that a brain does loses its force. He writes:

The system [involving the Chinese population] would need to have over a billion parts each with a number of states of its own (say, ten each). Between these states there would have to be a vast, intricate system of just the right causal connections, so that given this state pattern, then this state pattern will result, given that state pattern, then that state pattern will result, and so on. To realize the functional organization in question, these conditionals cannot be mere regularities (where this state pattern happens to be followed by that state pattern on this occasion); they have to be reliable, counterfactual-supporting connections, such that this state pattern will be followed by that state pattern whenever it comes up.

It is not hard to see that about 10^{10^9} such conditionals will be required of a system in order that it realize the appropriate functional organization, if we suppose a division into a billion parts. … Once we realize how tightly a specification of functional organization constrains the structure of a system, it becomes less implausible that even the population of China could support conscious experience if organized appropriately. If we take our image of the population, speed it up by a factor of a million or so, and shrink it into an area the size of a head, we are left with something that looks a lot like a brain, except that it has homunculi—tiny people—where a brain would have neurons. On the face of it, there is not much reason to suppose that neurons should do any better a job than homunculi in supporting [conscious] experience. (Chalmers 1996, 249–253, emphasis added)

This defence of functionalism along with Block’s objection ratifies, rather than resists, CPR. For functionalism entails that the Chinese nation or homunculi can bring about a realisation of the function of an individual person. Readers sceptical of functionalism owing to the entailment of CPR and the possibility of the Socially Realised Brain are encouraged to remember that the purpose of this paper is not to convince you of functionalism; rather, the point is to convince you of what follows for trinitarianism if functionalism is consistent and conceivable. At any rate, readers uncomfortable with standard functionalism at this point might be more comfortable thinking about what follows in terms of some anti-physicalist version of functionalism on which only immaterial substances can realise minds.

Towards the third person of the trinity

CPR is good news for the trinitarian. For CPR entails that: if (i) God¹ brought about a maximally accurate re-realisation of his person-type exactly once (yielding God²) and if (ii) God¹ and God² interacted in ‘the right kind’ of ways, then that could itself bring about a further re-realisation of God¹. Let’s call this potential third person God³.

To see that CPR entails this, recall the Socially Realised Brain. In that case we have a group of individual human persons that engage in coordinated activities in ways that ensure the existence of a further person whose internal psychological and phenomenal states are just like that of some arbitrary human person. Let us alter the case somewhat to make it more applicable to trinitarian concerns:

Socially Realised Adam. It is possible that an adult human person, Adam¹, is perfectly cloned a billion or so times. Each clone is an exact physical duplicate of Adam¹ at some time t. Because of this each clone realises a token-distinct instance of Adam¹’s mind at t. Each is given a residence somewhere on earth as well as the (shocking) knowledge of the fact that they are Adam¹ clones. After this, each clone of Adam¹ is given a part-time job: each spends a portion of their day interacting with the other clones with radio equipment by following instructions that allow them to collectively realise the type of functional organisation of that Adam¹’s brain realised at time t. In this way, the population of clones collectively bring about a realisation of one additional token-distinct instance of Adam¹’s mind at t. This clone has the same internal psychological and experiential states that Adam¹ had at t. Call this final instance of Adam¹’s mind that results from the activity of the clones ‘Adam³’.

The thing to keep in mind is that Socially Realised Adam is just a special instance of Socially Realised Brain. So if Socially Realised Brain is entailed by functionalism, so is Socially Realised Adam. Furthermore, if these are possibilities entailed by functionalism, then the following is likewise a possibility entailed by functionalism:

The Socially Realised God³. There is a possible situation in which God¹ and God² engage each other in ways that bring about a realisation of a further, maximally accurate instance of God¹’s person-type.

How could God¹ and God² ‘engage’ each other in ways that are capable of realising another instance of the mind of God¹? One way would be to do it in the way it’s done in the case of the Socially Realised Adam. A more traditional trinitarian approach could lean into the love motif noted in the introduction to this section. Perhaps God¹ and God² are drawn to each in love and decide to become a we, continuing their existence and activities in a profoundly close degree of communion and enjoyment of each other. Perhaps this would move them to participate moment-to-moment in infinitely many mental communicative acts that involve joint deliberation, joint preference ordering/negotiation, joint celebration of things worth celebrating, and mutual enjoyment of each other’s company. The result of this activity could be such a profoundly complex performative agent that it actually brings about the realisation of another individual instance of God¹’s person-type.²² There are different stories one could tell. But here’s the main point: if functionalism entails that individual persons can be produced through the activity of individual persons, then it follows that it is possible for God¹ and God² to intentionally engage each other in such a way that their joint activity re-realises God¹’s person-type once again.²³

Now, God¹ and God² are realised in the same divine system, so if the joint activity of God¹ and God² that yields God³ were also to take place completely within that one divine system, then God³ would himself be realised in that same system. Furthermore, God³ would arguably inherit his knowledge, power, and rationality from God¹ and God². Recall that God³, on this view, is a re-realisation of the mind of God¹ that results from the mutual activity of God¹ and God². This implies that when God³ decides to act or plan or communicate, that will be a manifestation of the joint activity of God¹ and God² deciding to do so. In which case, God¹ and God² will also throw their power behind that decision. At the very least it is a logical possibility.

This explanation for the existence of God³ raises a concern: if God³ is a distinct person, what is to stop God¹ and God² from engaging God³ in ways that realise a fourth divine person? There are at least two ways to address this issue. First, it could be a contingent matter that God¹ and God² do not engage God³ in this way. In which case, the fact that God is tripersonal would be contingent. This is fully compatible with Weak Functionalist Trinitarianism.

But there is another way to address this issue. Take a simple analogy involving a very small corporate board, administrative group, or leadership team. Such groups may form performative (/collective, /group) persons. While they are far too simple to plausibly yield a further individual person the analogy will remain useful. So let the Board be a performative person that is made up of exactly two individual members: Mel and Meg. Now let us ask: can Mel (or Meg) interact with the Board? For example, can Mel interact with the group of which she is a part by bringing proposals to the Board for consideration, by arguing with the Board’s past views, by challenging the Board’s future plans, and so forth? Yes, obviously. But in order to do so Mel must either interact with herself or with Meg. But when Mel interacts with her group in this way, she does not bring forth any further performative persons even though she is interacting with the Board.

Now, the magnitude and variety of interactions between God¹ and God² that would be needed to bring about God³ would be immense and for that reason quite different from the previous example just given. But there remains a way the divine case parallels the analogy to small performative persons. For suppose God¹ wants to, say, communicate something to God³. To do that, God¹ would have to interact with that which realises God³. But that would involve either interacting with himself or with God². But why should God¹’s interactions with himself or God² be expected to produce any additional individual beyond the individual those very kinds of interactions already produce, that is, God³? The very idea that they could is as strange as thinking that Mel’s engagement with the Board generates a further performative person. Stranger still is the idea that such interactions must produce a fourth person. For it seems at least possible that such actions fail to do so. We can state the point here as an independently attractive conditional: if an individual person x results from the complex interpersonal interactions of some other people y¹-yⁿ, and y¹-yⁿ only engage x by further interpersonal interactions with y¹-yⁿ, then it is possible that that activity does not yield any person in addition to x. Perhaps we could strengthen the consequent from a ‘possibly not’ claim to a ‘cannot’ claim. But the former is all that is needed to defend the consistency and conceivability of the functionalist account of the trinity.²⁴

At this point we can appreciate the argument for Weak Functionalist Trinitarianism:

Weak Functionalist Trinitarianism: If role-functionalism is both consistent and conceivable, then it is both consistent and conceivable that God is a single being who is exactly three distinct persons because there is one primary divine person who interacts with exactly one system-sharing re-realisation of his own person-type.

We have, at this point, provided evidence for a conditional resolution to the inconsistency and intelligibility aspects of the trinitarian trilemma. That is, conditional on a suitable version of functionalism being both consistent and conceivable, there is a consistent and conceivable functionalist version of trinitarian monotheism.

A concluding concern

A referee observed that functionalists generally point to composite substances (like brains) as that which instantiates person-types – where composite substances are wholes with proper parts. But the traditional trinitarian view is that the divine substance is simple, lacking proper parts. This raises a question whether the functionalist approach to the trinity fits with the simplicity of the divine substance.²⁵ I’ll make two points in response. The first point is about ‘keeping good company’ while the second point is about what evidence there is that functionalist trinitarianism is at least logically consistent with the simplicity of the divine substance.

While functionalist trinitarianism is distinct from existing views of the trinity it has important structural similarities to the prominent constitution view of the trinity defended by Rea (2020) and Brower and Rea (2005). They write that:

…the Persons of the Trinity can also be conceived of in terms of hylomorphic compounds. Thus, we can think of the divine essence [substance] as playing the role of matter; and we can regard the properties being a Father, being a Son, and being a Spirit as distinct forms instantiated by the divine essence, each giving rise to a distinct Person. As in the case of matter, moreover, we can regard the divine essence not as an individual thing in its own right but rather as that which, together with the requisite ‘form’, constitutes a Person. Each Person will then be a compound structure whose matter is the divine essence and whose form is one of the three distinctive Trinitarian properties. On this way of thinking, the Persons of the Trinity are directly analogous to particulars that stand in the familiar relation of material constitution. (Brower & Rea 2005, 68–69; cf. Rea 2020: 215–216 emphasis added)

According to the functionalist view of the trinity defended above there is one divine system (substance, essence) that instantiates three token-distinct functional organisations, where each organisation gives rise to a token-distinct divine person. This similarity between the constitution view and functionalist trinitarianism should not be surprising. For it has been argued that functionalism just is a hylomorphic account of the mind, where our minds are owed to the form of our brains much like our fists are owed to the form of our hands (cf. Grim 2008, 13). Indeed, many credit Aristotle himself with the view that minds are hylomorphic compounds in a way that can be read as a prototype of recent functionalism.²⁶ While there are these similarities between the functionalist theory developed in previous sections and Brower and Rea’s approach, the functionalist theory is firmly anchored in the philosophy of mind and provides details where Brower and Rea left their view at a relatively high level of abstraction.

The possibility that this paper’s functionalist account of the trinity is but one instance of Brower and Rea’s constitution view of the trinity will surely raise further questions. But for present purposes it doesn’t matter if the functionalist account is in fact a specific instance of their general kind of account, or if the functionalist account is only very similar to their account. What matters is the high degree of similarity. For it is this degree of similarity that supports the following modest point with regard to the question of the simplicity of God’s substance:

Common Company. If a constitution view of the trinity is consistent with the divine substance being simple, then the functionalist account of the trinity will likely also be consistent with the divine substance being simple; and if a constitution view of the trinity requires that the divine substance be composite, then the functionalist account of the trinity will likely also require this.

As far as I can tell, Brower and Rea provide hints that their model of the trinity is (as they envision it) consistent with either view of the divine substance, but they are light on details.²⁷

Here’s my second remark on this issue. There is at least some reason to think that the functionalist and the constitutionalist approaches to the trinity can preserve the simplicity of the divine substance. Martin Pickup (2016) has given a consistent metaphysical model of the trinity in which the distinct persons (Father, Son, and Spirit) share a single simple substance. Pickup’s model begins from the notion of spatially extended simples (objects that occupy multiple regions of space while lacking proper parts). Imagine an extended simple rod R which occupies several continuous points in space S1…Sn. R may instantiate a range of properties. For example, it may instantiate a colour property such that it’s red where it is located in the left-half of S1…Sn, but blue where it is located in the right-half of S1…Sn. But we cannot say that R’s left-half is red since R is an extended simple. It has no halves and is best described as instantiating an ‘irreducibly distributional property of being red-and-blue-in-the-appropriate-ways’ (Pickup 2016, 435).

Pickup then introduces a notion of ‘person-space’ analogous to physical space, where person-space is the space of possible persons (person-types), and each occupied point in person-space is a person (Pickup 2016, 421). He argues for the consistency of the idea that ‘the single and simple entity that is God is located at three distinct points of person-space’, where each occupied point corresponds to a distinct person of the trinity (Pickup 2016, 424). Since we are not forbidden from interpreting the relation of occupancy in person-space as requiring a substance to instantiate a person-type, Pickup’s model of the trinity can be taken as evidence for the consistency of the idea that a simple divine substance occupies three points in person-space in virtue of instantiating three distinct divine person-types.²⁸

This provides evidence that the functionalist account of the trinity is logically consistent with the simplicity of the divine substance. For Pickup’s model of the trinity is argued to be consistent with the idea that (i) the Son depends on the Father while the Spirit depends on both (Pickup 2016, 429), and his model also appears consistent with (ii) the members of the trinity being able to interact with each other, and (iii) the idea that each member of the trinity themselves hosts various mental states (beliefs, preferences, intentions, conscious states, etc.) that stand in various psychological dependency relations to each other.²⁹ Now, if it’s logically possible for the dependency relations in (i)–(iii) to be instantiated by a simple divine substance, then it also seems logically possible for other dependency relations to be instantiated by the same simple divine substance. For example, it’s consistent with Pickup’s model that the psychological dependency relations among each person’s mental states are instantiated in virtue of the instantiation of the non-psychological dependency relations characteristic of the functional organisation types that realise person-types. It is, at any rate, unclear what principle would allow us to say that the simple divine substance can instantiate the robust dependency relations in (i)–(iii) but not instantiate the non-psychological dependency relations that functionalists identify as realisers. But what is most important for present purposes is that conditional on functionalism we should not expect there to be any such principle. For functionalism entails that points in person-space can be occupied by a substance only if it instantiates a functional organisation type that realises a person-type.

So provided we lack sufficient reason to think (i)-(iii) are inconsistent with Pickup’s model or functionalism, we may draw a modest conclusion: there is noteworthy evidence for the logical consistency of a version of functionalist trinitarianism that takes the divine substance to be simple and yet capable of instantiating the properties necessary for realising the person-types of God¹, God², and God³. Perhaps, this will be unsurprising in the end. For Pickup himself says that ‘Points in person-space…are not entities. This may be unpalatable to some: they may be disconcerted that we can, using the term “Father,” refer not to an entity but to a way of being a person’. Pickup called this a cost (2016, 435). But this is very close to the functionalist idea that persons are not substances, but ways for substances to be. Far from a cost, functionalists will find this a virtue.³⁰