Many people, over the centuries, have labeled the Trinity as polytheistic. How can the Father, Son, and Holy Spirit be one God? In response to this criticism, Christians have offered a variety of replies. One reply is to simply affirm the unity of the Trinity, without any attempt to counter the charge of contradiction. Another explanation, common amongst the Greek Orthodox, is to view the Father as the unique principle of the Son and Spirit’s deity, thus grounding the unity of God in the person of the Father. For the theologian Karl Barth, the Trinity is the revelation of God’s eternal, free decision to be for humanity. Others have offered precise explanations, but explanations which revive old heresies. This is true with some contemporary analytic philosophers, whose framework for understanding the Trinity seems to imply Tritheism.
In this post, we will see how Aquinas solves this problem, particularly by looking at his understanding of the Father’s unique role within the Trinity. Aquinas, in this writer’s opinion, represents a healthy approach to Trinitarian theology. He acknowledges that the knowledge of the Trinity is something apprehended by faith, as it is beyond the grasp of the human intellect (ST Ia Q. 32.1). But Aquinas also seeks to understand the Trinity, to reflect by use of reason on that which we know by revelation. In this way, he steers a middle course between two types of theologians: those who use reason to arrive at knowledge of the Trinity, and those who refuse to use reason to reflect upon the Trinity.
Before we examine Aquinas’s doctrine of the Father, it is first necessary to provide biblical evidence that the Father’s “fatherhood” is really proper to his person. Restated: we will establish that the relationship of the Father to the Son is not merely a creational relationship, something which is true only after the Incarnation of Jesus. In Matthew, Jesus says: “No one knows the Son except the Father, and no one knows the Father except the Son, and those to whom the Son chooses to reveal him”(Matt 11:27, NIV). These terms Father and Son, in this passage, seem greater than simply assumed roles. Rather, they appear to reflect proper relations. Another passage of interest is John 16:28: ” I came from the Father and entered the world; now I am leaving the world and going back to the Father.” Here the term Father appears to describe a proper relationship of Jesus to the Father, a relationship true even prior to the Incarnation. Though we allow the possibility that “Son of God,” in scripture, might not always imply a proper relationship, as in Romans 1:3, wherein Jesus is declared the Son of God at the resurrection, we think it is best to acknowledge that in many passages, Father and Son refer to relationships which are proper, relations that are more than titular, belonging essentially to the persons.
Aquinas’s treatment of the Father occurs, amongst other places, in his Summa Theologiae (Ia Q. 33.1). Aquinas believes that the Father is the “principle” of the Deity, meaning that the Son and the Holy Spirit have their deity from the Father. He writes that the term principle “signifies only that whence another proceeds.” In this way, Aquinas is in concord with some Greek Orthodox theologians, who view the Father to be the principle of the Son and Spirit.
Although calling the Father “principle” is a shared affirmation with the Greek Orthodox, Aquinas next posits an idea that has been rejected by most Greek theologians. Aquinas uses a phrase called “relative opposition,” a big phrase which simply means that Fatherhood is only understood in terms of its opposite, namely Sonship, and that the procession of the Spirit is only understood with reference to its opposite, namely the spiration of the Spirit (the principle by which the Spirit proceeds). Aquinas’s big move is to say that these relations (these relations of “relative opposition”) are actually God himself. Restated: God is his inter Trinitarian relations.
To say God is his relations does not negate the personhood (hypostases) of the Father, Son, and Spirit, but it does imply that the persons are relations. That, of course, is impossible for us to grasp, as for human beings relations and persons are distinct, though certainly interconnected. But not so with God, at least according to Aquinas. God the Father is his paternity (his begetting of the Son).
Aquinas writes: “the Father is Father by paternity. Therefore He is the same as paternity” (Ia Q. 40.1). And “if paternity be removed, the hypostasis (person) of the Father does not remain in God, as distinguished from the other persons”(Ia Q. 40.3). Aquinas’s point, if we might restate his proposal, is that God the Father is not the Son because he is paternity, meaning that the Father is distinguished from the Son in that it is impossible to be both Father and Son in the same way, as these terms are opposed to each other. The Father is the same as the Son in every way, only what the Son has by way of Sonship (filiation), the Father has by way of Fatherhood (paternity). Likewise the Father has the identical deity as the Spirit, only the Father has it by way of Spiration (by breathing out the Spirit) and the Spirit has it by way of procession (by proceeding from the Father). Although Aquinas has a unique view of the Spirit’s relationship to the Son and the Father together, we have no time to discuss that. Yet it is sufficient to end on this note: the Father has the identical deity of the Son and Spirit, only the Father has this deity as the unique principle.