Augustine knows by faith that God is a trinity, Father, Son and Holy Spirit, and he is seeking as far as possible to understand what he believes. In the first seven books Augustine begins by searching the scriptures of the Old and New Testaments for clues to understanding, and then argues in the language of philosophy and logic to defend the orthodox statement of the doctrine against the Arians. In the last eight books Augustine seeks to understand the mystery of the divine Trinity by observing an analogous trinity in the image of God, which is the human mind; and in so doing he also...