HYPOSTASIS, in theology, a term frequently occurring in the Trinitarian controversies of the 4th and 5th centuries. According to Irenaeus (i. 5, 4) it was introduced into theology by Gnostic writers, and in earliest ecclesiastical usage appears, as among the Stoics, to have been synonymous with οὐσία. Thus Dionysius of Rome (cf. Routh, Rel. Sacr. iii. 373) condemns the attempt to sever the Godhead into three separate hypostases and three deities, and the Nicene Creed in the anathemas speaks of ὲξ ἑτέρας ὑποστάσεως ἢ οὐσίας. Alongside, however, of this persistent interchange there was a desire to distinguish between the terms, and to confine ὑπόστασις to the Divine persons. This tendency arose in Alexandria, and its progress may be seen in comparing the early and later writings of Athanasius. That writer, in view of the Arian trouble, felt that it was better to speak of οὐσία as “the common undifferentiated substance of Deity,” and ὑπόστασις as “Deity existing in a personal mode, the substance of Deity with certain special properties” (οὐσία μετά τινων ἰδιωμάτων). At the council of Alexandria in 362 the phrase τρεῖς ὑποστάσεις was permitted, and the work of this council was supplemented by Basil, Gregory of Nazianzus and Gregory of Nyssa in the formula μία οὐσία, τρεῖς ὑποστάσεις or μία οὐσία ἐν τρίσιν ὑποστάσεσιν.
The results arrived at by these Cappadocian fathers were stated in a later age by John of Damascus (De orth. fid. iii. 6), quoted in R. L. Ottley, The Doctrine of the Incarnation, ii. 257.