Plotinus related this also in terms of Aristotle's theory of cognition, with with Procession corresponding say to the power of sight when it is still groping for vision, and Reversion to the same power actualised by the contemplation of the object.

Plotnus' successors interpreted this somewhat more elaborately.  An anonymous commentator on Plato's Parmenides, who would seem to belong to the School of Porphyry (although whether or not he actually was Porphyry is more dubious, although still possible), recognised in Plotinus' account of the emanation of the Nous a phase of Rest prior to Procession and Reversion, during which the Nous is identical with the Primal One.

Such a telescoping of the hypostases and identification of the Nous with the One was unacceptable to later Neoplatonists.  However, both Iamblichus and Proclus still agreed with the commentator in dividing emanation into three phases, those of Abiding, or immanence in the Cause, Procession from that Cause, and Reversion back upon it.

This triad was also no longer applied simply to the emanation of one Hypostasis from another, but thanks to the principle of correspondence became a universal law inherent in the structure of everything that exists.  It is equated with the Plotinian triad (also adopted and modified by Gnosticism) of Being, Life and Intelligence, the Chaldaean triad of Existence, Power and Intelligence, the Aristotelian triad of Substance, Potentiality and Actuality, Plato's Philebus' triad of Limit, Unlimited and the Mixture of the two, and the mythological triad (as interpreted through the Orphic poemms and the Chaldean Oracles) of Cronos, Rhea and Zeus.

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Neoplatonism