ETERNITÀ. – It is the proper measure of the divine nature, absolutely immutable in its simple fullness and in the totality of its presence—of its own being: unlike time, which measures mutable things both with regard to being and with regard to activity (bodies), and unlike the evo, which is the measure of things immutable in being but mutable in activity. The determinations of e., time, and evo are therefore made according to the process and mode of possession of being and life—as St. Thomas repeatedly observes—and not with regard to having a beginning and an end; only if the “presence” of being is absolute and complete, both as regards its constitutive principles and its activity, is there e., which the Angelic Doctor defines with Boethius: “Interminabile vitae tota simul et perfecta possessio” (Sum. Theol., 1ª, q. 10, a. 1; cf. Boezio, Cont. philos., V, prosa 6: PL 63, 858).
Of e., as the infinite duration of divine life, man cannot have a proper and adequate concept: just as he grasps the divine nature and its attributes only by analogy with bodies, so he also thinks of its immobile duration according to an absolute presence, in contrast to the continuous flow and alteration of physical phenomena (time), and also above the successions of the higher processes of spiritual substances. Thus, whereas the instant in material substances bears only upon a fraction of being and is in continual movement forward, and whereas in spiritual substances, although it is stationary with respect to being, it is subject to succession (discontinuous, because it depends especially on the free will of the spirit itself) with respect to activity, in God the instant rests in the full possession of self and of being. We therefore imagine e. as the actuality of the instant extended to infinity, but in reality what we perceive as actuality in the temporal instant is only its flowing and therefore the imperfection of its being. E., on the other hand, is conceived as immobile fullness, and thus the instant, passing from time to e., overturns—as it were—its ontological quality: “Dicendum quod nunc stans dicitur facere aeternitatem, secundum nostram apprehensionem. Sicut enim causatur in nobis apprehensio temporis eo quod apprehendimus fluxum ipsius nunc, ita causatur in nobis apprehensio aeternitatis, in quantum apprehendimus nunc stans” (Sum. Theol., 1ª, q. 10, a. 2, ad 1). If St. Thomas intends to admit the possibility for man of some perception of e. itself, one must think of experiences of the greatest interior concentration in the higher sphere of intelligence and love, when the soul is carried outside its habitual contact with the visible world and, as it were, stretches out in surrender toward God, who attracts II. Characteristic in this regard is the “vision of Ostia” described by St. Augustine in the Confessions (IX, 10), where e. is spoken of, as God is spoken of (Ev. 3, 14), as that in which properly “there is not” a past or a future, but only a present—that is, the simple positing of being in its metaphysical purity: in this sense, whereas of creatures it must be said that they “exist,” of God alone must it be said that he “is” (Sum. Theol., 1ª, q. 12, a. 1, ad 3). Kierkegaard likewise writes: “God does not think (abstractly), he creates; God does not exist, he is eternal. Man thinks and exists, and existence separates thought and being, holding them outside one another in succession” (Postilla conclusiva, S. V., VII, 2ª ed., Copenaghen 1925, p. 32). In his anti-metaphysical position, the Protestant K. Barth, by contrast, seems to conceive e. as a kind of absolute time and as the synthesis of the moments of time: “E. is not at all without time (zeitlos). It is rather the place of origin of time, properly speaking eminent, absolute time, that is, the immediate unity of present, past, and future, of now, before, and after, of middle, beginning, and end, of movement, origin, and goal” (Die kirchliche Dogmatik, III, 1: Die Lehre von der Schöpfung, Zurigo 1945, p. 72). The error here lies in conceiving e. as perfect time and in conceiving time itself as perfection; whereas time is given only in radical otherness with respect to its moments (past, present, and future), so that to affirm the “unity” of its moments is to destroy the reality of time: consequently, an imperfection that cannot be purified within the metaphysical sphere is inherent in the succession entailed by such otherness. E., evo, and time are attributes of being and therefore derive directly from the being to which they relate their own nature. What is created, therefore, is the being by participation, which may be either in the evo or in time; evo and time concern the being and perfections of the being by participation: it is being and these perfections that consequently possess the ontological positivity as such in which the finite truly participates, and from which the intellect ascends to conceive the infinite. E. Brunner too, who conceives e. as mere “fullness of time” (Erfüllung der Zeit), as “full temporality” (Vollzeitlichkeit), remains within a sphere of evident theological empiricism (Die christliche Lehre von Gott, Dogmatik, I, Zurigo 1946, p. 287).
The concept of e. in Christian theology must therefore be distinguished from that of thought which has remained at the cosmic meaning of everlasting duration (the evo, αἰών, duration without beginning or end). Thus Anaximander speaks of “cyclical generations and destructions according to an indeterminate eternal duration” (ἐξ ἀπείρου αἰώνης: H. Diels-Kranz, Die Fragmente der Varsohnather, 3ª ed., I, Berlino 1935, 83, 31); Anaximenes speaks of a “movement of the e.” (Κίνησις ἐξ αἰώνης: ibid., I, 91, 31); it is an attribute of the cosmos for Pseudo-Philolaus, since the world remains ἐξ αἰώνης καὶ εἰς αἰών (ibid., 8, 117, 11); Heraclitus attributes e. to the Logos (λόγον αἰώνα: ibid., I, 161, 13). In this first sense, e. is the “duration without beginning or end” of the cosmos, according to Aristotle’s declaration that it “has neither beginning nor end of its entire duration (ἀρχὴν μὲν καὶ τελευτὴν οὐκ ἔχων τοῦ παντὸς αἰῶνος), but has and contains within itself unlimited time” (De oulo, II, 1, 283 b. 26 agg.). For Plato, on the other hand, e. is an attribute of the immobile Ideas, and time is derived from e. as its “moving image” (εἰκώ... παντὸν τινὰ αἰώνος: Tim., 37 D). Plotinus, in his Treatise on E. and Time (Enn., III, 7), deepens the dependence of time upon e. to such an extent that he makes it arise not from the measure of the physical world but from the soul of the world: e. appears as the absolute stability of the intelligible world and in this sense is identical with God (καὶ ταὐτὸν τῷ θεῷ: Enn., III, 7, 5). Proclus abandons this conception and makes e. a hypothesis in its own right, from which e. derives to all eternal things, just as temporal things participate in their temporality from time, going so far as to admit a distinction between that which is eternal, its e., and e. in itself: θῆλον ὅτι ἄλλο μὲν αἰώνιον, ἄλλο δὲ ὁ ἐν τῷ αἰωνίῳ αἰών, ἄλλο δὲ ὁ καθ'αυτὸν αἰών: Elem. Theol., prop. 54, ed. E. R. Dodda, Oxford 1933, p. 50, 26). E. is expressly elevated to the status of a divine hypothesis in the cosmogonies of the genetic systems, each of which has its own “pleroma” or intelligible world, and Jesus is presented there as “the advocate of the future e.” (παρὰ λῆτος τῷ παρελθόντι αἰώνι: Clemente Alessandrino, Stromata, ed. O. Stählin, Berlino 1936, VII, p. 114, 21).
Nella filosofia moderna invece il concetto di e. ha perduto ogni propria consistenza metafisica ed è ritornata ad essere l'attributo della realtà, del mondo, della sostanza, della coscienza... cioè di quanto si attribuisce la qualità di assoluto nell'ambito dell'essere: l'e., che in Spinoza resta come « sub quo infinitam Dei existentium concipimus » (Cog. metaph., I, 4; ed. Van Vloten-Land, 2ª ed., III, L'Aia 1895, p. 201) scompare nell'idealismo oggettivo di Hegel per il quale l'e. non è che il « risultato » del dispiegamento del tempo, così come lo Spirito assoluto (Dio) è il risultato della sua attività nella storia del mondo (cf.: Philosophie der Weltgeschichte, 3ª ed., I, ed. G. Lasson, Lipsia 1930, p. 50).
Secondo la dottrina cattolica l'e. per essenza è
propria di Dio, le creature possono esser dette « partecipanti » l'e. « seconda che godono di qualche perennità di esistenza. Ciò vale per lo stesso mondo fisico a parte post nel suo complesso; benché i singoli esseri corporali siano corruttibili, la fine del mondo non sarà il suo annientamento ma una trasformazione con « cieli nuovi e una terra nuova » (II Pt. 3, 13). In un senso più proprio partecipano dell'e. le creature spirituali che sono immortali individualmente; ma la più alta partecipazione all'e. è quella che s. Tommaso chiama « secundum operationem sicut Angeli et beati qui Verbo fruuntur » (Sum. Theol., 1°, q. 10, a. 3) che sono nel pieno possesso della « vita eterna ». Ma sono da dire eterne anche le pene dei demoni e degli empi nell'inferno contro la teoria di Origene della finale « restituzione » o reintegrazione (ἀνακτήστασις) alla felicità dei medesimi, e la cessazione dell'inferno (Denz-U, 211). Per l'immanentismo moderno questa dottrina non è affatto un dogma, ma una « questione puerile » (eine Kinderfrage: J. Kant, Die Religion innerhalb der Grenzen der blossen Vernunft, ed. K. Vorländer, Lipsia 1937, p. 76), poiché la coscienza è realtà e legge a se stessa.
Nella scolastica medievale si disputò a lungo sulla possibilità in astratto (cioè « de potentia Dei absoluta ») di una creazione del mondo « ab aeterno »: negata dalle scuole d'ispirazione platonico-agostiniana, fu invece affermata energicamente da s. Tommaso per il quale « mundum non semper fuisse sola fide tenetur et demonstrative probari non potest sicut et supra de mysterio Trinitatis dictum est » (Sum. Theol., 1°, q. 46, a. 2). A conferma della compatibilità metafisica fra creazione e esistenza ab aeterno del mondo l'Angelico cita il testo di s. Agostino: « Sicut si pes ex aeternitate semper fuisse in pulvere, semper subesse vestigium quori a calcarte factum nemo dubitaret » (Sum. Theol., loc. cit., ad 1; Agostino, De Civ. Dei, XI, 4; PL 41, 319). Un mondo che fosse « ab aeterno » avrebbe sempre nel suo svolgersi il carattere della temporalità e l'e. non sarebbe tanto in lui quanto da parte della volontà divina nel crearlo « ab aeterno », così come si manifesta ora nel conservarlo « in aeterno ».