I don’t consider myself actually knowledgeable enough to explain Neoplatonism itself very well, but I probably talk about it often enough that I ought to try explaining at least what I mean by it. If a more knowledgeable reader needs to set me straight on any of what I’ve written, please feel free!
I like to proceed like Ficino did, by outlining some of the different sorts of things we encounter in the thought of Neoplatonism. The summary below won’t be exhaustive in that respect, but it gives us the basic idea, I think.
The physical world exists. Most people today will agree with that, and so do the Neoplatonists. They affirm the corporeal realm around us. It exists. But, as they remind us, it’s not everything. It can’t explain consciousness.
Consciousness exists too, undeniably, and it’s not quite the same as the world around it.
But consciousness and corporeality can’t be everything either. The mind, you see, perceives not just trees and stars and fields, but also the invisible commonalities between them, the treeness and starness and fieldness that allow us meaningfully to group things into kinds. Those unseen unifiers are outside time and outside space, unlike their instantiations, undecaying and unaffected. This is the domain inhabited by such things as the truths of mathematics.
So then we have the world of bodies around us, the presence of consciousness within us, the realm of universal, unchanging truth above us. But that’s still not quite all. None of this will seem completely unfamiliar to the thinking of contemporary philosophy. But the Neoplatonists do take one step further and ask what is above the realm of timeless truth. What is first?
Today we might venture to suggest that it could be God, and then trot out our prefabricated definitions about what this God must be like. Could this thing possibly be what’s first?, we would then ask.
The Neoplatonists don’t do that. Not quite. They begin by trying to find that highest, greatest origin of all things, and ask what it would have to be, and then, afterwards, they see if it can be suitably called divinity. (Spoiler: they find that nothing could more suitably receive that name.)
It is the One, the indivisible unity behind all other unities — the purest simplicity. Neoplatonists realized that anything other than perfect unity could not be the origin of everything else, since it would be made up of parts (even if its only multiplicity were in the form of metaphysical composition, eg as actuality and potentiality), and those parts would be more basic than their whole, in one respect, and thus prior in the order of reality.
So the first thing must be absolutely simple, and it must be, indeed, Simplicity itself. If it were simple without being Simplicity, then it would be an instantiation of a prior universal which would itself be first.
So then it is Simplicity, pure Unity, that is first, is alone.
Everything else in reality pours forth from the metaphysical abundance and fecundity of the One. How do we know? We know because the One is not the only thing, and because everything that exists participates in the One (ie, everything that exists is itself one).
And Neoplatonism claims, of course, that Plato understood at least something of this, if not all of it, and that the metaphysical reflections and questions that arise in the dialogues have their place and their answers within precisely this account of reality.
I think Neoplatonism offers assistance in a lot of the metaphysical and epistemological difficulties that beset philosophy today. I don’t mean to say that it can be conclusively proven true; maybe it can be, but that’s beyond my mind to know. For me though, to treat Neoplatonism as the default starting point (rather than, say, materialism) seems at the very least to be greatly advantageous for the student of philosophy.