[It is remarkable that Augustin, understanding thoroughly the distinction between essence and person, should not have known the difference between οὐσία and ὑπόστασις. It would seem as if his only moderate acquaintance with the Greek language would have been more than compensated by his profound trinitarian knowledge. In respect to the term “substantia”—when it was discriminated from “essentia,” as it is here by Augustin—it corresponds to ὑπόστασις, of which it is the translation. In this case, God is one essence in three substances. But when “substantia” was identified with “essentia,” then to say that God is one essence in three substances would be a self-contradiction. The identification of the two terms led subsequently to the coinage, in the mediæval Latin, of the term “subsistantia,” to denote ὑπόστασις.—W.G.T.S.]