HYPOSTASIS, in Theology, a word employed to denote the personality of the Second Person of the Trinity. The word employed by the Greek fathers to denote the Godhead, without reference to the distinction of persons, was ousia (essentia). Substantia was, by the Latins, used in the same way, though Hilary makes it equivalent to hypostasis, when he speaks of three substantiae in the Godhead. But there was still another term, the ambiguity of which produced continual controversies in the early church. This was the word substantentia, which was at times used synonymously with ousia, and at other times synonymously with hypostasis. Hence the Roman and African churches, in 347, at the synod of Sardes, pronounced the belief of three hypostases in the Godhead to be heresy. Athanasius expressly declares that hypostasis is exactly the same thing as ousia (essentia). Yet it had been determined against the Sabellians at the synod held at Alexandria in 319, that there was one ousia
(essentia), and three hypostases in the Godhead. The confusion was in a great measure remedied by the discussion at Alexandria, A.D. 362, at which Athanasius presided. To his discretion the favourable result was mainly owing. It was now agreed that hypostasis should be taken in the stricter sense, so that, while there was one ousia (essentia) in the Godhead, there were three hypostases, or persons.