Now what was the step taken by these theologians – especially the latter one? It was a sharper distinction between the concepts which were used, and had to be used, for the Trinitarian dogma. I give you now two series of concepts where each side has three words, meaning the same.

The first series is:One Divinity One essence (ousia) One nature (physis) The second series :Three substances (hypostasis) Three idiotetes (properties) Three prosopa (personae) If you have these three terms, on each side, you could perhaps best use the following in the one case: mia ousia (one essence) and three substances. The Divinity is one power of being – that is what ousia, essence, nature, means. But this one power of being, which is Divine, has three forms in which it expresses itself, three independent realities. This means the Divinity is not a species, (as man is a species, for three of you who are sitting here in the class, but under one and the same power. Son and Spirit come out of the same Abyss, of the Father, and always remain in it even if they become independent. All three have the same will, the same nature, the same essence, Nevertheless the number three is real: each has His special characteristics or properties. The Father has the property of being ungenerated; He is from eternity to eternity. The Son has the characteristic of being generated, although in eternity. The Spirit has the characteristic of going out, of proceeding from the Father and the Son. But these characteristics are not differences in the Divine essence, but only in their relations to each other. Now this was complicated and very abstract philosophy, but it was the formula which made the reunion of the Church possible – one essence, three persons; one nature, three faces or countenances.