Here is a very short summary paper I presented in Dr. McCall’s ST 9000 Trinity and Atonement course at TEDS. I had to summarize Augustine’s On The Trinity in 1,000 words. It was difficult. Here you go, enjoy!
In his masterful work, De Trinitate, Augustine embarked on a rigorous journey through biblical texts, logical reasoning, and psychological models in order to defend the full deity, as well as the unity, of the Father, Son, and Holy Spirit in the Christian doctrine of the Trinity. Though this book is as much a work of apologetics as it is of dogmatics, Augustine’s ‘proofs’ come from Scripture. He is careful to present his models and analogies of the Trinity as helpful aids to conceptualize that which is ultimately incomprehensible, but never as dogma. Throughout this work, Augustine’s wisdom, humility, and piety are evident as he treats the most difficult Christian doctrine, explaining that “nowhere else is a mistake more dangerous, or the search more laborious, or discovery more advantageous.” In this short paper I will summarize Augustine’s major arguments presented in De Trinitate and provide a brief reflection. As Augustine asked his readers in the beginning of his work, so I ask my audience, “let us set out along Charity Street together.”
Augustine begins his defense of the Trinity with the full deity of the Son by utilizing the qua move. In order to make sense of the biblical witness which at times “appear to be in flat contradiction with each other” Augustine distinguished between the form-of-a-servant rule and the form-of-God rule concerning the Son. Qua form-of-God, the Son is creator of all; qua form-of-a-servant, i.e. incarnate, the Son was made of a woman and born under the Law. With this tool in hand, Augustine is able to dispel apparent contradictions in the hypostatic union with ease and lead the reader back onto sure footing.
But while his qua move untangles various textual issues, it cannot solve every problem. For instance, the problem of subordinationism: doesn’t the fact that the Father sends the Son demonstrate the superiority of the Father? And if this is the case, wouldn’t it make the sent Son, who is then inferior to the Father, less than the true God? Augustine answers this line of reasoning by making a distinction between substance-wise predications and relationship-wise predications. Relationship-wise predications are a functional category and thus are different from a predication that speaks about substance. With this distinction in place, Augustine is able to argue that the Father and Son are coeternal and consubstantial while affirming that the nature of their relationship is such that the Father sends the Son. He will later use this distinction to argue for the consubstantiality of the Father, Son, and Spirit, while upholding their functional differences. Thus, ad intra, the Father begets the Son, The Son is begotten of the Father, and The Sprit proceeds from the Father and the Son. Ad extra, the Father sends, the Son is sent, and the Spirit proceeds from the Father and from the Son ad extra as he does ad intra. So, in summary, though God is one in substance, we can distinguish between the persons of the Trinity by their relations ad intra and by their functions ad extra.
In arguing for the consubstantiality of the Holy Spirit with the Father and the Son, Augustine also argues that the Holy Spirit is the love or charity between the Father and the Son. If the Father is the lover, and the Son is the beloved, then the Holy Spirit is love, “he is that by which the two are joined each to the other.” Thus, since he is common between the Father and the Son, and due to the doctrine of simplicity, the Spirit is one in substance with the Father and the Son. The Trinity, then, is united in one substance or being, while the three persons are able to be distinguished by their relations to one another.
Augustine then moved from his more biblically grounded arguments for the full divinity of the Son and Spirit towards less biblically grounded, though not necessarily anti-biblical, meditations on models for understanding the unity and diversity of the Trinity- which were mostly drawn from human psychology. He justified this method not by some bottom-up, proto-Feuerbachian projection of the mind onto God, but rather in the top-down fact that mankind is made in the image of God and thus, reasoned Augustine, our psyches ought to display our Creator’s Trinitarian fingerprints on them. So, he began this project with mind, knowledge, and love. While these three aspects of human psychology can be spoken of in isolation, ultimately, they are grounded in the mind. Furthermore, knowledge is begotten of the mind, but love is not. Love joins knowledge to the mind, but it is not the offspring of the mind as knowledge is. Augustine later rejected this model- after dragging the reader through a painstaking dialectic- in favor of his most mature model which employs memory, understanding, and will.
In this later model, Augustine argues that memory, understanding, and will do not belong to three separate lives, but to one life. They are not the faculties of three separate minds, but of one mind, one substance- though functionally, they are distinct. Augustine adds a caveat that this Trinity of the mind requires self-reference in order for it to work properly, i.e. the mind remembering, understanding, and loving itself. But his admirable piety did not allow him to stop there. Augustine went on to argue that mere self-reference is not the true end goal of the mind, but rather, the Trinity of the mind is a true Trinity and image bearer when contemplating its eternal maker. When the mind is distracted in contemplating finite realities, however, it cannot be said to truly image God.
All in all, Augustine lamented that his attempt at understanding produced more effort than results and he attributed the inadequacy of his final model to the discontinuities between the human subject, who is one person, and its Tri-personal Creator.
At times I was overwhelmingly frustrated by Augustine’s method of meticulously arguing for a proposed solution, only to then reject it with the brush of his pen. Still, I found the broad sweep of his project edifying. But while I found a few of his proposals odd or a bit too slick, nothing gave me pause quite like his understanding of women as image bearers. For Augustine, women bear God’s image when united in one flesh with man, but otherwise they are not God’s image bearers, but rather man’s image bearers. Though I recognize his effort to makes sense of 1 Cor. 11:7, this line of thought continues to baffle me. But, despite his self-proclaimed inadequacies, the man was a genius and the way he approached the subject of the Trinity with fear and trembling is a great example for all of us who open our mouths to speak of God.
 For explicit qua move uses: 82, 87, 99.