SUBSISTENCE. — In general, it indicates the consistency and sufficiency of reality that a substance (v.) attains through the possession of its essential and real principles. Subsistence therefore constitutes the mode of being of the individual substance that is complete in itself, in contrast to the inherence that is proper to accidents: “illud dicimus subsistere, quae non in alio sed in se existunt” (Sum. Theol., 1a, q. 29, a. 2, c; cf. q. 75, a. 2 ad 1).
Subsistence is thus the actuality of substance as such: “Ratio substantiae est quod per se subsistat” (St. Thomas, In III Sent., dist. 6, q. 1, q. 1, a. 1 c), so that subsistence coincides with the individual substance existing in itself. As the actuality of substance, subsistence is realized in different beings according to their respective ontological structure. In God, subsistence consists in the simple and full possession of being as pure actuality (cf. Sum. Theol., 1a, q. 13, a. 11). And since, for St. Thomas, the perfection of being is graduated according to the independence that a substance has with respect to matter, subsistence belongs principally to spiritual natures that have no matter in themselves, but are pure forms: such are the angels, which are therefore called “subsistent forms” (ibid., 1a, q. 3, a. 3, c). Even the human soul (v.), although it is the substantial form of the body, must be recognized as endowed with subsistence insofar as it exercises the operations of understanding and willing, which manifest its spiritual nature (ibid., q. 75, a. 2; cf. Q. de anima, a. 14).
To clarify the terminology, one can therefore distinguish: a) the essence (v.) or nature (v.), which is the formal constituent of any thing; b) the “primary substance,” i.e., the real individual or “hypostasis” or “supposit,” which is the concrete existing reality in its ontological sufficiency (cf. Quodl., II, q. 2, a. 2, c); c) subsistence denotes the actuality of this primary substance, by which it exists in itself and is distinguished from abstract essences or “secondary substances” that exist only as concepts in the mind and in reality through the individuals that realize them; d) the person (v.) adds to subsistence the dignity of a rational nature.
The development of the notion of subsistence coincides with that of reality: for Plato, universals subsist because they constitute the “in itself” of the real, withdrawn from the becoming of sensible appearance (cf. Resp., 476 A ff.). In Aristotelian metaphysics, although in reality subsistence belongs to the individual substance, it is nevertheless the effect of “form,” and it is therefore the species as such that subsists amid the vicissitudes of physical contingencies, while individual things are born and die (Met., VII, 3, 1028 b 36-1029 a 2). In Neoplatonism, subsistence, indicated by the term “ὑπόστασις” (the Aristotelian meaning of the term is foreign to this metaphysics: cf. H. Bonitz, s. V. in Index Aristot., Berlin 1870, 801 b 35-802 a 8), corresponds to indefectible existence, “ἀνακλείστος ὑπόστασις,” which emanations obtain in their derivation from the One (cf. Proclus, The Elements of Theology, ed. E. R. Dodds, Oxford 1933, prop. 8-4, 94: pp. 78, 6; 84, 24 and passim). Moerbeke translates with subsistentia the title of Proclus’ lost Greek treatise on the problem of evil: De malorum subsistentia, and appropriately so, as Cousin observes, because “bona habent ὑπόστασις, mala tempore ὑπόστασις,” inasmuch as “bonum species, malum sine specie ac velut privatio” (Procli opera..., I, Paris 1820, p. 188). In its original Greek meaning, therefore, subsistence as ὑπόστασις is “foundation,” both in the transitive sense from ὑπόστασις and in the intransitive sense from ὑπόστασις: in the ontological sphere, it belongs, if it belongs to the singular substance with respect to accidents, also “both for Plato and for Aristotle” to the universal essence with respect to individuals. Greek philosophy therefore stands for the real identity of οὐσία and ὑπόστασις, of subsistentia or ὑπόστασις with substance (first and second).
This identification is found in the Greek Fathers and passed into the condemnation of Arius at the Council of Nicaea (Denz-U 54), but after the Council, it was St. Athanasius who clarified the precise meaning of subsistence as primary substance, sanctioned by the formula: μία οὐσία, τρεις ὑπόστασις (cf. Athanasius, De incarn. et contra arianos, 10: PG 26, 1000 B: μία γάρ θεότης καὶ εἰς θεός ἐν τρισὶν ὑπόστασις). At this point, in theology, the transition begins from subsistence as οὐσία-ὑπόστασις to that of “person” (πρόσωπον), but, as is well known, among the Greek and Latin Fathers there was not always perfect agreement on this point: the fluctuating use of