399–419

Augustine, On the Trinity: from the unity of substance to the Persons, relations and psychological analogies

Augustine's fifteen books On the Trinity gather the achievements of earlier fathers and, according to González, set the course of Western trinitarian theology; Berkhof sees in them the completion of the Western conception of the Trinity. Unlike the Cappadocians, who moved from the diversity of the hypostases to the unity of the ousia, Augustine begins with the essential unity of God: the Father, the Son and the Spirit are the one first cause of all things, "not three almighties, but one almighty". He defines the distinctions of the Persons as "relative" – neither substantial nor accidental. He seeks the image of the Trinity in the human soul, created in the image of God: memory, understanding and will (love) make up one mind.