Is the doctrine of the Trinity an irrational idea? Does it discredit Christianity?
The ecumenical councils used Scripture as their authority, but sought to work out the doctrine of the Trinity in an intellectually rigorous way. The early theologians were philosophers and brought these categories of thought to bear on the debates. After all, if God is a rational being, His revelation must make logical sense, though this is different than being fully comprehensible to finite minds. Presumably, they also accepted the proposition that one cannot believe what one considers irrational and applied their knowledge and skills diligently to work out a rational explanation of the doctrine. So theology and philosophy must interact, in the tradition of the church, to express the most accurate and logical doctrines possible as we continue to understand the revelation of the Trinity.
The orthodox doctrines were worked out using philosophic categories of person, substance, and nature. There was (and is) some disagreement about the meaning of these categories. Augustine, for instance, thought that it couldn’t be deciphered what the category of person referred to, just that it was three, whatever it was. Some modern theologians and philosophers are suspicious of importing our modern conception of person into the creedal categories. I start with the premises that there are personal similarities between God and human beings since we are created in His image, and that God is similar enough to us to carry on a personal relationship. In addition, God reveals Himself to us in ways that seem analogous to us as persons, so I will start with what we know of persons and reason from there about how God is personal. My approach is essentially that of a social Trinitarian. I think the following will demonstrate the rationality of this approach and its orthodoxy as well, nullifying the charges of tritheism.
God Is Three
A person is a category of immaterial conscious substance. There seem to be three types of persons that we know of: God, angels, and humans. Persons are essentially centers of consciousness. There are some capacities that are common to all persons: cognition, rationality, affect, volition, desire, perception, and morality, and capacity for relationship are examples. The possession of these capacities are sufficient (and perhaps necessary) to qualify a being for personhood. Personhood can be understood as a category of which there are subsets of kinds of persons that are marked off by capacities and properties that are unique to that subset in virtue of substance and nature (discussed below).
The creeds affirm that the Father, Son, and Holy Spirit are separate persons. Each would then be a center of consciousness with (minimally) the capacities of personal beings. The persons aren't identical with each other because they have properties that aren't identical. Each has a unique self-identity. The Father knows that "I am the Father" and doesn't know that "I am the Son." If the Father thought "I am the Son" He'd be confused. Each has His own mind, with unique contents; they do not share one mind. A distinction of what each person knows would be the propositions they know about themselves as a self-conscious being. The Father knows that He sent the Son. The Son knows that He was incarnate and died on the cross. The Spirit knows that He helps us believe. Each of these are propositions that only refer to one person of the Trinity. So the unique contents of their minds mark them off as unique persons. Each has the property of omniscience as God so each person knows all that the others know, but the Father does not know that “I was incarnate” as the Son knows that proposition. Thomas Morris has suggested that the persons share one mind but have unique self-identities and uses examples of split brain phenomena to illustrate this theory's plausibility. I reject views that God has one mind but three self-conscious identities. The analogies to split-brain phenomena ignore the fact that no matter how well someone can function with such a condition, the condition is still a pathology. God is not sick.
Volition and will are capacities of persons so each has His own will instead of sharing one. Most of the reading I’ve done seems to presume that there must be one will otherwise there would be potential for conflict. I don’t think that is a sufficient reason to deny what seems to clearly be a property of persons, as we normally understand the category. The text also hints at this idea that each person has a will. In the Son’s prayer to the Father in Gethsemene He is obviously expressing a different will than the Father’s. Others have worked this out differently than I, such as the two wills theory, that I don’t have time here to respond to and is more fully explored in the area of Christology. I will presume (with good reason) that Jesus had one will and it was different than the Father’s. So we have good philosophic and Biblical reasons for believing that each person of the Trinity has a unique power of will.
The distinction needs to be made between the power to will and the content of the will. It doesn’t follow that to have separate powers of will that necessarily will lead to conflict in the contents of will so that isn’t good grounds for rejecting this idea. There are two good ways to avoid this conclusion. The first is Richard Swinburne’s suggestion that the persons of the Trinity would willingly cooperate, submitting their wills to one another. This way all of their decisions and actions would be in unison and in agreement. He further suggests that they could delegate tasks to each person whose will would be decisive in that area.
The solution I prefer is an application of Aristotle’s ideal man. God is omniscient and knows all factors in every decision He would make. God is also omnibenevolent, supremely virtuous we could say, and knows the best thing to do in every situation. Given these two properties of God, there never could be disagreement among the persons of the Trinity because they would all arrive at the same conclusion of the best thing to do. And they would never change their minds since, knowing all true propositions, they would have already taken every factor into consideration. The will of God, then, could be spoken of univocally because the contents of their wills would be identical and their separate capacities of volition would be exercised in perfect unison.
The divine persons are also distinguished by their eternal relations. The Father begets the Son; the Spirit proceeds from the Father and the Son. Begetting and proceeding are asymmetric and areflexive relations that obtain between the three persons. Each person of the Trinity has a self-awareness of begetting, being begotten, or not being begotten; or proceeding, being proceeded, or not proceeding. Each person certainly distinguishes Himself from the others or knows His own properties – what is true about Him in relation to the other two. Part of what is true about each of them are these relations that help to distinguish them as unique persons.
Traditionally these relations have been held to be ontological dependence of the Son on the Father, and the Spirit on the Father and the Son. It's not clear to me what these relations mean ontologically other than categories we've used to distinguish them without much descriptive content to understand them. I'd like to toy with the idea of functional relations, common with the idea of the economic Trinity, to fill in these relations. In either case, ontological dependence and functional dependence doesn’t imply ontological subordination. In virtue of participating in the divine substance, all three persons are co-equal.
The idea of functional relations might be worked out this way. Each person of the Trinity has a different function or plays a different role in the deity. Begetting and proceeding are asymmetrical relations. The Father begets the Son, in that He sends the Son to accomplish the work of salvation. Perhaps since the Son is also called the Word, He also sends the Son to give the written revelation of Himself and His work. The Father begets and the Son is begotten or sent. The Father and the Son process or spirate the Spirit in that they send the Spirit to be our helper, to accomplish a personal work in believers in a very personal way. The Spirit proceeds in that He is sent on His role in the Trinity. This functional view of these relations help to distinguish the persons, but also might help to fill in the content of what those relations are while (hopefully) remaining orthodox.
Swinburne has also proposed the relation of love to distinguish the persons, but also to explain why three persons are necessary. In his explanation, love is a capacity that must be actively expressed in order to have it so there must be a minimum of three persons to express mutual and corporate love. I have doubts how this reasoning bears up when it is applied to other capacities God has. What other virtues does God have that must be expressed to be had? Mercy seems similar enough to love in that it is an action, not just a sentiment, that requires an object. If God is necessarily merciful, then the object of His mercy must be necessary, according to Swinburne's reasoning. Creation must be necessary, man's fall must be necessary, and redemption must be necessary. But these are all considered to be unobliged choices of God's. Swinburne must provide a non-ad hoc reason why love is unique among the virtues in needing expression if this explanation is to survive. It would be satisfying to have a good rational reason for why three persons, but it seems to me for now we are left with revelation for that fact.
Each person is divine insofar as they instantiate the divine nature, which is identical to the one divine being. There are three centers of consciousness that have being in one individuated nature of divinity.
God Is One
The Council of Nicaea affirmed that the Father, Son, and Spirit are one substance. Substances, or substantia, possess properties that make a thing what it is. The substance remains identical to itself through time and change. A substance is a natural kind that is marked off by a set of its ultimate capacities that are possessed by it solely in virtue of the substance belonging to its natural kind.
Substances possess properties and remain identical to themselves through time and change. Joshua Hoffman and Gary S. Rosenkrantz define substance in their book Substance: Its Nature and Existence:
X is a substance = df. X is an instance of a concrete category, such that: it could have a single instance throughout an interval of time (non-minimal).
A substance can be instantiated as an individual concrete particular, a member of a natural kind, that is traceable through a duration of time. The instantiation of a substance possesses the properties predicated of it. A substance is a natural kind that is marked off by “a set of its ultimate capacities that are possessed by it solely in virtue of the substance belonging to its natural kind.”
The divine substance (secondary substance) only has one exemplification (primary substance) so divine nature is coextensive with divinity. Most substances or natural
kinds can be exemplified multiple times, but the divine substance is exemplified only once. The divine substance or nature has essential properties that all three persons of the Trinity share, not as three instantiations of those properties but identical properties of divinity. There is one property of omniscience, for example, that all three persons share in virtue of sharing one substance. The Trinity has the properties of divinity plus the capacities of person, and this is what marks the Trinity off as a unique kind of person in the general set of persons. The divine properties allow the Trinity to operate through their capacities as persons to the maximum degree and quality possible.
Perfect being theology entails there is only one divine being, but I'm not sure this is a good reason. For reasons I've argued for above for three persons with distinct wills, it seems there could theoretically be more than one perfect being. Two maximally great beings would cooperate in such a way as to be in complete unison. Revelation does make it clear that there is one God, one exemplification of the divine substance and that is sufficient for affirming that only one being has the properties of divinity.
By using the plural of properties above I don't mean to imply that God has more than one property, though I also don't subscribe to Thomistic simplicity. Swinburne offers a tantalizing solution here in expressing all of God's properties as one: "pure, limitless, intentional power." God is perfect and always seeks to do the good. God always knows what the good is and there is nothing that prevents God from always doing the good. If God is perfectly free and omniscient, He is not going to fail to do the good because of weakness or irrationality. There is nothing external to God that limits what He can do; He is constrained only by His nature and logical possibility. Swinburne believes that it then follows that God is good. His argument doesn’t begin with goodness but demonstrates how it is entailed by properties of God. And all of God's other properties can be extracted from this one PLIP property.
The exemplification of any substance requires an individuator. I don’t intend to take up the argument here for what in particular that individuator might be – I’m not sure. But whatever it is, God has one individuator and it individuates the substance, not the persons. This avoids the charge of tritheism. The extension of the divine substance is one. In Swinburnian labels, the individuator of G1, G2, and G3 is in the G.
God exists of metaphysical necessity, but not logical necessity since there is nothing logically contradictory about God not existing. God may exist of modal necessity, that is if anything exists God must exist. Cosmological arguments seem to lead to the conclusion that God is the only sufficient cause of the universe. If the world exists God necessarily exists. In addition, it would seem that God must exist across all metaphysically possible worlds if He is a "maximally great being." Necessary existence (modally) would seem to be a maximally great-making property.
God Is Three & One
God is three persons, rational centers of consciousness, in one divine substance. There’s nothing contradictory in that. It is unusual because our normal experience is a one-to-one correlation of primary substances and persons, but rarity is not the same thing as irrational. The Trinity is not a doctrine the church would have affirmed had it not been revealed, primarily because there is nothing else in our experience like the Trinity. The Trinity is, however, rationally permissible to believe and Biblically obligatory for Christians to believe.
Conclusion: Unique, Yet Rational
God is a personal substance, but instead of the usual one-to-one correspondence of person and substance that we are familiar with, God is three persons in one substance. The divine nature, shared by all three persons of the Trinity, is instantiated only once. God is a union of three persons. Though unique, there appears to be no incoherence to the concept of three persons in one substance. Each person of the Trinity has the essential properties of the divine nature instantiated only once.
The early church took both the Bible and rationality seriously. The Bible was the authority and source of doctrine. But the early church was not fideistic; they brought rigorous theological and intellectual efforts to bear in working out the details of the doctrines of the Trinity and the implications this had for Christology. This approach was essential to define orthodoxy and defend the church against heresy. The Bible witnesses to the concept of the Trinity and the doctrine bear up under philosophic scrutiny. The ancient creeds of Christendom and the articulation of one of the most fundamental Christian doctrines are rational and commendable.