The later neoplatonist Proclus (412-485 CE) was head of the Platonic Academy in Athens, at a time when the Athenian Academy was somewhat notorious as the intellectual center of resistance to the spread of Christianity in the Roman Empire. Nonetheless, his work had a profound influence on the Arabic, Byzantine, and Latin traditions. He is usually cited as the main philosophical influence on the early Christian theologian pseudo-Dionysius, who was taken very seriously by Albert the Great and Thomas Aquinas.
Proclus wrote extensive commentaries on Plato, as well as an influential commentary on book 1 of Euclid’s Elements of Geometry. Hegel called him the greatest dialectician of antiquity. Though I think Hegel by his own principles really should have given that title to Aristotle, Hegel was right to recognize Proclus as important.
Aquinas is credited with recognizing that the Latin Book of Causes — a translation of the Arabic Discourse on the Pure Good — was mostly derived from Proclus’ Elements of Theology. Aquinas treated Proclus himself with considerable respect. Dietrich of Freiberg made significant use of his work, and his student Berthold of Moosburg wrote a very long commentary interpreting the Elements of Theology in Christian terms. The Renaissance theologian Nicolas of Cusa and the maverick Giordano Bruno were much inspired by Proclus.
Along with Spinoza’s Ethics, Proclus’ Elements shares the peculiar distinction of being written in a style visibly influenced by Euclid’s Elements. Euclid’s work has often been cited as a sort of paradigm of demonstrative reasoning. Though Proclus, unlike Spinoza, did not work from explicit definitions and postulates and used a looser style of demonstration, his Elements consists of theorems and a sort of demonstrations.
Proclus defends the neoplatonic idea of a One that transcends being, but as Gwenaëlle Aubry and Laurent Lavaud point out in the introduction to the French collection Relire les Éléments de théologie de Proclus (2021), perhaps his most influential idea is that of a very strong continuity from the highest principles to the most mundane effects, which has been read as a strong assertion of immanence as well as transcendence. He is an important source for all the later theological traditions that want to argue for simultaneous immanence and transcendence.
Proclus very explicitly crystallizes what I have called the generalized “unmoved mover” model of causality in Plotinus. For Proclus, “higher” and “lower” causes cooperate in the constitution of worldly things, but the higher cause is always more of a cause than the lower cause. At the same time, he rejects Plotinus’ identification of matter with evil, while emphasizing all of Plotinus’ more positive affirmations of the goodness of manifestation and the beauty of the cosmos.
In a separate treatise On Providence, he develops a sort of epistemic analogue to the generalized unmoved mover theory. “Providence” (pronoia — literally, “forethought”) is a knowledge-like thing that is superior to knowledge in that it is supposed to be eternal and unextended, and to involve no separation of what we might call subject and object. Proclus develops a subtle and suggestive account of something metaphorically like implicit, unextended “seeds” of forms within the overflowing of the One that transcends all extended form. While the One does not “know” worldly things, it “pre-knows” their unextended “seeds”, within something like what Schelling later paradoxically called the identity of identity and nonidentity.
In the Elements, Proclus argues for an interdependence of being, life, and intellect. While one obvious reading of this would emphasize a foundational role of spiritual beings in Proclus’ metaphysics, I am intrigued that it can also be interpreted as a somewhat “deflationary” account of being, closer to Aristotle, and far removed from later notions of pure abstract existence. We can’t begin to have an account of being, without also having an account of life and intellect. With his endorsement of a One beyond “being”, Proclus had no need for a commitment to a notion of pure “being”.