Idiotes, or ‘particularity,’ is the term chosen to express the individual characteristic. The difference between the Persons, says Basil (c. Eun. 1.19), consists in their plurality and in the ‘particularities’ which characterise each: and again (Ep. 38.8), everything that belong to Father is seen in the Son, and everything that belongs to the Son belongs also to the Father, since the Son abides whole in the Father and again possesses the Father whole in Himself; the hypostasis of the Son, so to speak, the ‘form’ and presentation (prosopon) of the recognition of the Father, and the Father’s hypostasis is recognised in the form of the Son; there remains the supplementary particularity with a view to the clear distinction of the hypostaseis. These particularities are called by Basil γιωριστικαι ἰδιότητες (‘identifying particularities’) (Ep. 38.5, c. Eun. 2.29), and they consist in being gennetos and being agennetos (c. Eun. ib.): or as in Greg. Naz. (Or. 25.16), agennesia, gennesis and ekpempsis (promission). They are modes of being, not elements in being. Later theology called them for obvious reasons ἰδιότητες ὑποστατικαί (pseudo Cyr. de ss. Trin. 9: “agennesia and gennesis and ekporeusis (procession): in these hypostatic particularities alone do the three holy hypostaseis differ from one another.”) In the form ‘idioma’ this term goes back to Alexander of Alexandria (ap. Thdt. h. e. 1.4.52), who states that being agennetos is the only idioma of the Father.
The fact that these particularities merely represent the modes in which, has been said, the divine substance is transmitted and represented, was expressed by the phrase τρόπος ὑπάρξεως, ‘mode of existence.’ The word hyparxis means, in the simplest sense, existence. Hypostasis and ousia, says Athanasius, (ad Afr. 4), means ‘existence;’ for they are, and they ‘exist.’ But the word carries a certain association with the sense of beginning. The hyparxis of life, remarks Irenaeus (haer. 4.20.5), comes about by sharing in God: Eusebius (eccl. theol. 1.9.2) states that when the Bible speaks of the hyparxis of created things, it testifies that they all were created through the Logos. It is therefore possible to argue that when the phrase ‘mode of hyparxis’ is applied to divine Persons, it may, at least in the case of the second and third Persons, originally have contained a covert reference not merely to their existence, but to the derivation of their existence from the paternal arche.
The terms seemed to have been rescued by Basil from the schools of logic, and subsequently adopted generally into the theological tradition. The word knowledge, he observes (ep. 235.2), covers many senses; an object may be known by reference to number, size, effect, mode of hyparxis, time of generation, or ousia; the Eunomians demanded that Basil should profess the knowledge of the ousia of God; but he hesitated to say more than he knew what knowable of God, and that the other knowledge of Him passed human comprehension. Again (de Sp. St. 46) he says that the Spirit is a living ousia, lord of sanctification, whose relationship to God is disclosed by His procession, but the mode of whose hyparxis is preserved ineffable. His friend Amphilochius of Iconium (frag. 15) insists that the names Father, Son and Holy Spirit do represent ousia as such, but “a mode of hyparxis or relation.”
In the fourth (pseudonymous) book of Basil against Eunomius, which may have possibly have its author Didymus, the blind theologian of Alexandria (inter Bas. ed. Ben. vol. i 283B), this point, that the term agennetos expresses not the ousia of God, but His mode of hyparxis is elaborately proved: for if the objects that have a different hyparxis of their being must be held to possess also a different ousia, then various members of the human race are not homoousioi, for Adam had one hyparxis, being formed out of the earth, and Eve had another, since she issued from Adam’s rib, and Abel another, as he was born of human intercourse, and the Son of Mary another, for He was born of the Virgin alone: hence agennetos and gennetos do not refer to the ousia of the Father and the Son, but to their mode of hyparxis. In this passage, the origin of existence is clearly taken as determining the mode of existence in each given instance of temporal being. It may be inferred that by implication the point stressed in the divine instances is also the process by which each Person comes to have His being imparted, as much as the manner in which that being, once imparted, is expressed. The Father affords a negative instance, as He does not come to be from any source but exists in underivatively; the Son comes to be derivatively, by generation, from the Father. The matter is however only one of academic interest, since, whether the term really means ‘mode of existence’ or ‘mode of obtaining existence’, in practice it is exclusively employed to cover the facts involved in the latter conception; while, on the other hand, since the relations between the divine Persons have no temporal reference but express eternal processes continually operative within the divine being, it might well be said that there is no difference for thought between those processes themselves and their initiation.
The phrase also occurs in Gregory of Nyssa (c. Eun., 3.6.63, vulgo 8, Migne 45.793A), at about the same date as in the example last quoted, but not in the technical Trinitarian sense. The instance does, however, further illustrate the association of the phrase with origins. Arguing against the view that the Son had a temporal beginning Gregory points out that the Son, as Creator, had no affinity with the creation; if He had such affinity with His works in any other respect, it would have been necessary to admit that He did not diverge from the creation in respect of the mode of His hyparxis either: but this is not the case. Pseudo-Justin several times employs the phrase of the Trinity, as, for instance, when he states (exp. rect. fid. 3) that the terms agennetos and gennetos and ekporeutos did not express ousia but modes of the hyparxis; or when he says (ad orth. resp. 139) that the divine Persons differ not in ousia but in their modes of hyparxis, and that this difference in modes of hyparxis does not destroy their unity in ousia. Pseudo-Cyril (de ss. Trin. 8) repeats that the Holy Spirit proceeds from the Father, not by way of generation but by way of procession—it is, he adds, another mode of hyparxis, just as is the generation of the Son; and he compares Adam, who was in the literal sense agennetos, Seth, who was gennetos, and Eve, who “proceeded” from Adam’s side. The whole passage, with much else, is transcribed by John of Damascus into the first book of his Orthodox Faith (fid. orth. 1.8, 135B, C). Maximus Confessor again (myst. 517B) remarks the Holy Monad is a triad in its hypostasis and mode of hyparxis.
So far the connections with origins appear to be maintained. Nevertheless, Leontius of Byzantium employs both tropos (mode) of hyparxis and logos (principle) of Hyparxis in relation to the two natures of Christ (c. Nest. & Eut. prol., Migne 86.1269C; ib. 1, 1304B). In this connection the phrases have no reference to origins, but mean simply ‘mode of existence,’ or ‘constitutive principle’. The same remark applies to the passage (ib. 1285A) in which the phrase is applied to the human soul, which is said to be circumscribed both on its own principle of hyparxis and through being associated with a circumscribed body. In like manner John of Damascus (c. Jacob. 52) remarks the incarnation was not an act of the divine nature, but the mode of a second hyparxis. The possibility therefore remains that the association with origins is mainly an accident, arising from the inherent nature of the case when the phrase was applied to the divine Persons. But in any event, as has been said, it makes not practical difference to the the sense. The term mode of hyparxis was applied, from the end of the fourth century, to the particularities that distinguish the divine Persons, in order to express the belief that in those Persons or hypostaseis one and the same divine being is presented in distinct objective and permanent expressions, though with no variation in divine content.