A culminância da dialética plotiniana é a união mística com o Uno, numa contemplação extática, segundo foi exposto, com maior profundidade, no capítulo anterior. Henosis é a palavra grega para designar essa união. No caminho da "conversão", que caracteriza o itinerário da "inteligência espiritual" no homem, Plotino   aponta para além da intelecção, para a pura intuição do Uno, que é simples e sem alteridade. Aqui, a alma prescinde de toda razão discursiva e de toda ciência. Trata-se de um estado hiper-racional, que tem como um dos momentos preparatórios a reflexão, a virtude, a ascese.

O que significa união mística? Uma co-presença com o divino, atemporal, em que a alma entra na posse e unidade máxima de si mesma, para alcançar a similitude com o Uno (homoiosis to Theo). Pela henosis, é superada a distância entre a alma pura e a divindade e alcança-se a perfeita unificação com Deus já nesta vida. [Ullmann  ]

O Tratado 8 das Enéadas de Plotino, que Porfírio   reterá como último na ordenação que impôs, ilumina — com o permanente bemol que representa a pequena palavra hoion — mais uma espécie de despossessão de si que uma integral manutenção da singularidade individual em uma íntima união ao Uno. Que, no entanto, a introversão unitiva seja a princípio "dom" e "amor", capaz, sem que "se perca" Nele, de pôr o homem em relação de intensa proximidade com um Bem qualificado, no Tratado 3 (Enéadas V, 5, 12), — em termos muito antropomórficos para ser tomado à letra — de "benévolo" (epios) e de "favorável" (prosenes), — é o que atesta notadamente este Tratado 38 onde Plotino — ousando o que então lhe pareceu "temerário" — mostra a alma totalmente purificada que, pronta a conhecer uma imensa alegria (toson eupatheias), além dos desagravos do corpo, de todas as honras, de todas as riquezas do mundo e mesmo de todas as formas do "saber", realmente "só no Só" (mone Monon), não mais dois mas todos os dois um: (oud’eti duo, all’hen ampho", Enéada VI, 7  , 34). [Maurice de Gandillac, Plotin]

Admittedly, Proclus   later disagreed with Plotinus’ view (in Farm. 948,14-20) because he took it to be allied with Plotinus’ belief that part of our soul never ceases its unconscious contemplation of the intelligible Forms. But Proclus in Ale. 1 5,13-14, following Iamblichus   ap. Proclum in Ale. 1 11,11-17, and like the Anonymous Prolegomena to Platonic Philosophy ch. 26, holds that the starting point for Plato and the whole of Philosophy must be the Delphic saying ‘know thyself’, studied in Plato’s First Alcibiades  . This fits with Plotinus’ insistence, which influenced Augustine  , that we must look for the chief levels of reality, the Intellect and the One, within ourselves, 1.6 [1] 9 (8); 5.8 [31] 10 (31-43); 6.9 [9] 7 (16-23). Plotinus’ most famous autobiographical account of his experience of union with the Intellect in 4.8 [6] 1 (1-11) starts by saying that he has often withdrawn from everything else into himself. Even the phenomenological character of the experience is taken to indicate how things really are. There is not merely a sense of timelessness; the Intellect, and one’s self as united with it, are really timeless, 3.7 [45] 11. There is not merely a loss of sense of where one’s own boundary stops and that of Intellect or the One begins, 6.5 [23] 7 (14-17); there is genuine union. Plotinus holds more generally that the source from which something stems is within it, and he applies this to the hypostasis Intellect: Tor in turning back (epistrephein) on itself, [Intellect] turns back on its source’ (Plotinus 6.9 [9] 2 (35-6)).

Cary (Phillip Cary, Augustine’s Invention of the Inner Self, Oxford 2000, ch. 3) has argued for Augustine’s invention of the Inner Self, and has distinguished Augustine from Plotinus as inviting us to look not only in ourselves for God, but first in and then up. But not only does Plotinus also recognise more than one level. (The characteristic ratiocinative self is below the intellect of soul, which is a higher self; there are many levels of self; the human Intellect is in turn derived from the divine hypostasis Intellect; the One is beyond Intellect again). But more importantly, Plotinus puts more into the inner world than Augustine, since he locates everything divine within. Only the sensible world remains outside. [SorabjiPC3:13]

(Armstrong Selection and Translation): [The experience of the mystic union described.]

This is what the command given in those mysteries intends to proclaim, ’Do not reveal to the uninitiated.’ Because the Divine is not to be revealed it forbids us to declare It to anyone else who has not himself had the good fortune to see. Since there were not two, but the seer himself was one with the Seen (for It was not really seen, but united to him), if he remembers who he became when he was united to That, he will have Its image in himself. He was one himself then, with no distinction in him either in relation to himself or anything else; for there was no movement in him, and he had no emotion, no desire for anything else when he had made the ascent, no reason or thought; his own self was not there for him, if we should say even this. He was as if carried away or possessed by a god, in a quiet solitude, in the stillness of his being turning away to nothing and not busy about himself, altogether at rest and having become a kind of rest. He did not belong to the realm of beauties, but had already passed beyond Beauty and gone higher than the choir of the virtues, like a man who enters into the sanctuary and leaves behind the statues in the outer shrine. They are the first things he looks at when he comes out of the sanctuary, after his contemplation within and his converse There, not with a statue or image but with the Divine Itself; they are secondary objects of contemplation. That other, perhaps, was not a contemplation but another kind of seeing, a being out of oneself, a simplifying, a self-surrender, a pressing towards contact, a rest, a sustained thought directed to perfect conformity, if it was a real contemplation of That Which was in the sanctuary: if one does not look in this way one finds nothing. These are only images, by which the wise among the soothsayers express in riddles how That God is seen. A wise priest reads the riddle and makes the contemplation of the sanctuary real by entering it. Even if one has not been There, and thinks of the sanctuary as something invisible, the Source and Principle, one will know that one sees principle by principle and that like is united with like, and will not neglect any of the divine properties which the soul can have. Before the vision one seeks the rest from the vision; and the rest, for him who has gone higher than all, is That Which is before all. Soul is not of a nature to arrive at absolute non-existence. When it goes down it comes to evil, and so to non-existence, but not to absolute non-existence; and when it travels the opposite way it comes, not to something else, but to itself; and so when it is not in anything else it is in nothing but itself. But when it is in itself alone and not in being, it is in That; for one becomes oneself not being but beyond being by that intercourse. So if one sees that one’s self has become this, one has it as a likeness of the Divine; and if one goes on from it, as image to original, one reaches the end of one’s journey. And when a man falls from the vision, he wakes again the virtue in himself and considers himself in all his order and beauty, and is lightened and rises through virtue to Noûs and through wisdom to the Divine. This is the life of gods and divine and blessed men, deliverance from the things of this world, a life which takes no delight in the things of this world, escape in solitude to the Solitary.