Just as modalism attempts to explain the nature of the Godhead in simplistic, analogous terms, so does the teaching of tritheism; however in the opposite manner. The premise of tritheism is the existence of three equal, but completely autonomous beings, each of which possesses the inherent qualities of a divine being. This may seem to be a blatantly ridiculous proposition on its face; however subtleties within the claims can actually easily lead to a properly orthodox view on the Trinity, slipping into the area of tritheism. This is a much greater danger than in the case modalism. Even in the case of early church writers, such as the Cappadocian fathers — Basil of Caesarea, Gregory of Nyssa, and Gregory of Nazianzus (writing in the late fourth century) — tritheism appears to rear its ugly head in the foundational thought of the doctrine of the Trinity. The issue initially presents itself with the problem of analogy. One such analogy used by proponents of tritheism is the following thought experiment: imagine three human beings. Each of the them is distinct; yet they share a common humanity. So it is with the Trinity; there are three distinct persons, yet with a common divine nature. This analogy was even used by Gregory of Nyssa in order to establish an approach to thinking about the Trinity in terms of personhood. Ironically this was done in his work That There Are Not Three Gods. So clearly no intent was present to smuggle tritheism into the conversation; however one is still left with a sense that tritheism is not far from the rationale of such analogous reasoning.
The most robust definition of the Trinity during the patristic period, can be traced to the Eleventh Council of Toledo, held in 675 A.D. Only eleven bishops met in this Spanish city to dialogue and set forth a clear and proper definition of the Trinity. This event would actually set the standard for doctrinal integrity with respect to the Trinity. The view of the western church as well as many writers in later medieval discussions, were strongly influenced by the course charted by these eleven men in Toledo. The crux of the issue delved into by the Council, was the relation of the terms “Trinity” and “God”, and how the intersection of these words gives rise to a more relational perspective of the Trinity. We can read the summation of their conclusions, where they state:
“This is the way of speaking about the Holy Trinity as it has been handed down: it must not be spoken of or believed to be “threefold” (triplex), but to be “Trinity”. Nor can it properly be said that in the one God there is the Trinity; rather, the one God is the Trinity. In the relative names of the persons, the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance. Although we profess three persons, we do not profess three substances, but one substance and three persons. For the Father is Father not with respect to Himself but to the Son, and the Son is Son not to Himself but in relation to the Father, and likewise the Holy Spirit is not referred to Himself but is related to the Father and the Son, inasmuch as He is called the Spirit of the Father and the Son. So when we use the word “God”, this does not express a relationship to another, as of the Father to the Son or of the Son to the Father or of the Holy Spirit to the Father and the Son, but “God” refers to Himself only.”
This is perhaps one of the more concise descriptions of the harmony that exists between the terms “God” and “Trinity”. The oneness of God as a being is only to be considered in a trinitarian sense by virtue of relation among persons. It is as if the perspective from which one looks determines the definition one chooses to utilise. As stated earlier, balance with respect to the Trinity is a tall ask of theologians and biblical scholars. Much relies on the adherence to the fundamental understandings of “being”, “substance”, and “person”. At a basic und simple level, God can be defined as a “being” of one “substance” and three “persons”. The approaches as well as the conclusions vary depending on the school of thought, or the thinker in question. The best way to wrestle with these ideas is to truly wrestle with the ideas in all their forms and even extremes; then to formulate an independently crafted understanding of the Trinity while remaining faithful to the biblical evidence.