Substantia Propter Quid: Understanding Why the Trinity is not Tri-Theism

When considering how the Father, the Son, and the Holy Spirit are all God (in the sense of having “Godhood” predicated of themselves) and yet not individual Gods (tri-theism), it is helpful to understand the difference between an individual substance and a substantial kind.

The doctrine of the trinity affirms the following triad:

1. There is one God.
2. God is tri-personal (God consists of three persons who subsist in and share equally in the same divine nature). 

          2.1. God is personal, not a person.

     3. The persons are eternally and simultaneously existent.

This triad affirms that there is one God whose nature is endowed with three centers of consciousness [1]. Although we sometimes speak of God as being a “person,” this is not, technically speaking, correct. From a Christian point of view, God is personal (hence, (2.1)). Consider the following propositions:

P1. God is a person

P2. God is three persons.

According to the law of non-contradiction, you cannot have A and not-A at the same time and in the same sense without yielding a contradiction. If the subjects and predicates of P1 and P2 are used in the same sense and with reference to the same time, then a contradiction has obtained. In other words,  God cannot be one person and three persons in the same sense and at the same time. (2) allows for this contradiction to be avoided. Finally, in accordance with proposition (3) of the triad, the persons exists eternally and simultaneously together. Thus, Modalism is avoided [2].

THE CHARGE OF TRI-THEISM

Can the doctrine of the Trinity avoid tri-theism, though? Oxford theologian, Alister McGrath, writes that “Tritheism invites us to imagine the Trinity as consisting of three equal, independent, and autonomous beings, each of whom is divine” (McGrath, Christian Theology: An Introduction). In other words, contra (1), tri-theism maintains that there are three Gods. A misunderstanding of the Trinity that has led people to accuse Trinitarian theology of endorsing tri-theism is revealed in the following anthropic triad:

1`. There is one human nature.

2`. There are multiple human persons.

3`. These persons exist at the same time.

In the same way that there is one human nature (in the sense of genus or kind) and yet multiple human persons, so there is one divine nature (also in the sense of genus or kind) and three divine persons who are also separate beings. There can be three separate, individual, human persons who nonetheless are of the same genus -- homo sapien. In the same way, it is thought that the Trinity affirms the existence of three individual gods who are of the same genus -- "homo divinitatus" (I made that word up. Don't go looking for it in the literature). But this is simply tri-theism, right? Right. I will be arguing, however, that the anthropic triad above is not analogous the doctrine of the trinity. 

My basic thesis is that a proper understanding of substance kinds and individual substances alleviates the charge of tri-theism and can elucidate the coherence of the historic notion of the Trinity (see forthcoming work on the coherence of three persons who are equally God). 

INDIVIDUAL SUBSTANCES AND SUBSTANCE KINDS

The council of Nicea was careful to use the greek word “ousia” to identify the essence that was shared between the three persons. In english, “ousia” is “substance,” but should not to be confused with the kind of substances that are spoken of in chemistry or physics. Rather, philosophically speaking, a substance represents that which stands under or grounds some thing -- it is an ontologically basic thing. The council of Nicea agreed that Jesus and the Father (and later, the Holy Spirit) are of the same substance. That is to say, the Father, Son, and Holy Spirit are “consubstantial” -- homoousia. It is not merely that the members of the Trinity are united in purpose and character, although this is certainly true. Rather, they are united in virtue of sharing or being of the very same substance. 

Consider, now, the difference between individual substances and substance kinds (primary and secondary substances, respectively). Aristotle spoke of primary and secondary substances, where primary substances are particular things (cats, horses, etc.), and secondary substances are universal kinds of substances (species or genera) that can be instantiated in numerous, distinct things. My cat, Purdy, is a primary substance -- an individual -- but “cathood” is the secondary substance that she instantiates -- the kind. What’s more, there are various individual human substances of the broader human kind. For example, Joel Ballivian and Tyler McFarland are both individual human substances -- they are ontologically basic and independent things -- and, consequently, they are both in the broader category of human substance kinds. However, while Joel and Tyler may share a common substance kind (i.e. homo sapien), they do not share the same individual substance (i.e. they share the same secondary substance, but not the same primary substance). 

Regarding the Trinity, then, it should be understood that (1) affirms that there is one individual, divine substance. There are not three individual substances of the broader homo divinitatus substance kind (this is affirmed by (2)). One should not, therefore, understand the multiple instantiations of human nature as parallel or analogous to the instantiation of the Godhood substance kind. Each human person is an individual substance of a certain kind, but these individuals are separate beings from one another (substantially distinct in virtue of being their own individual substances), even if they share the same substance kind. The members of the Trinity, on the other hand, are not individual substances of a divine kind. Rather, they are persons who "subsist" in the same primary substance. There is one individual "God-substance," not merely a divine substance kind (a secondary substance) that is instantiated by three individuals. Thus, my Trinitarian triad above could be reinterpreted as the following:

1*. There is one, individual (primary) God-substance.

2*. This individual substance (primary substance) is tri-personal; three persons subsist in and share the same divine substance.

   2.2*. This individual substance is personal, not a person. 

3*. These persons are eternally and simultaneously existent.

CONCLUSION

While this may seem strange, it is not illogical. There is nothing about being an individual substance that logically excludes the subsistence or ownership of multiple persons within that substance. There is one God -- one primary divine substance -- in which three centers of consciousness (persons) subsist. Tri-theism maintains that there are three primary substances of a secondary, divine kind. Thus, the charge of tri-theism can be avoided in virtue of the fact that the persons of the trinity share a consubstantial nature -- not consubstantial in kind, but consubstantial with respect to the same individual substance. 

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Footnotes:

[1] The Athanasian Creed affirms that "we worship one God in Trinity, and Trinity is unity; neither confounding the persons nor dividing the substance."

[2] There are two kinds of Modalism: Chronological and functional. Historic orthodox Christianity has denied both, for good reasons.