EVO. — From Gk. αἰών (αἰτῶν : Lat. aevum) it denotes time, the duration of something, so that according to the varying conception of being there arise various and conflicting notions of e.
Among the pre-Socratics αἰών indicates a certain “period of time,” e.g., the duration of a man’s life: thus Empedocles speaks of an e. “unfailing” (ἐμπεδόχος αἰών: fr. B 17, 5); Anaximenes (fr. A 6), Anaximander (fr. A 10) and Empedocles himself (fr. B 16, 2) speak of an e. “immense” (ἀστέος αἰών). In Plato, through a process of development not fully clear, the world of the senses becomes the visible image (εἰκών) and time becomes e. as the intermediary (Tim., 37 d–38 b). The development is clearer in Aristotle, who, treating of the duration of celestial bodies, after saying that his predecessors with divine insight (θείασις) had introduced αἰών to denote the total duration proper to each being: τό γάρ τέλος τό παράγον τόν ἦτος ἐκστόχος γάρων, οὗ μήδεν εἶναι κιττό σύνων..., goes on to affirm that “for the same reason” αἰών can be said to denote the infinite duration of all the heavens and the totality of time stretching to infinity: “this meaning, Aristotle notes, is fundamental and original because αἰών comes from ‘being always’ (ἀπὸ τοῦ αἰτίου) and hence is ‘immortal and divine’ (ἐξίστιχος καὶ θεός: De coelo, I, 9, 279 a. 23–28). There thus remains, as in Plato, an intimate connection between time and eternity, but eternity is placed within nature itself.
This was well perceived by Plotinus (Enn., III, 7; περί αἰώνες καὶ πρόγον), who, taking up the position of the Timaeus, frees αἰών from all dependence and inserts it into the physical world to place it in direct connection with the soul and the intelligible world, making it a property (αἰτίαστος): “in no way can it be that the quality of being absolutely unchanging of that of which one cannot say that it was or will be, but which simply is, the stable being that admits no alteration in the future and has not changed in the past… perennial life” (Enn., loc. cit., III, 7, 3). Yet in the development of Neoplatonism Proclus criticises Plotinus himself, for, faithful to his theory of the hypostases and the technique of participation, he places αἰών above the infinite and time above its image: thus before all eternal things there exists eternity in itself, and before temporal things time (Procli elementa Theologiae, prop. 52–53, ed. L. R. Dodds, Oxford 1933, p. 50 sqq.). According to Dodds (loc. cit., p. 228) Proclus brings together a development of Greek thought, including Aristotle, down to magical doctrines: thus the plural αἰώνες is found and there is a hypostasised and defined Αἰών which is its principle and almost its substance.
In St Augustine the Platonic conception is filtered through his experience of conversion and becomes the eternity of transcendence as the point of convergence of history both of peoples and of individuals (infantia, pueritia, adolescentia…). In Aristotelian Scholasticism, on the other hand, e. becomes the intermediate duration between time and eternity, proper to incorruptible beings (celestial bodies, intelligences), and St Thomas calls it “participated eternity” (cf. Quodl., V, 4, 7; Sum. Theol., 1a, q. 10, a. 5), which, with the loss of the incorruptibility of the stars, remains the exclusive property of spiritual creatures. E. is thus the duration and the measure of the duration of finite spiritual substances that have being distinct from essence (In I Sent., dist. 19, q. 2, a. 2; ed. P. Mandonnet, I, Paris 1929, p. 471), or the fullness of being of their immutable essence as spiritual reality.