One of the first things we figured out about being/the real/ a thing was that it is transcategorical, which is easiest to visualize by saying that it can never be a node or a branch on a Porphyrian tree. So long as you are trying to grasp it by the rules of definition you will never locate all that you mean by it. That cluster of ideas that the Greeks tried to catch with on or the Latinate with ens is just as appropriate to the top of the tree as to the bottom, since only the lowest level of the tree escapes logical existence and only the highest level of the tree can be said of all things. There is even a reason to put it somewhere midstream in the tree, as when philosophers divide “being” into “real being” and “mental being”.
Some responses and corollaries that have been drawn from this:
1.) We can see “the one” as both the one in number and what includes all things, and all that arises between as our concepts. So taken, The One is beyond all conceptualization. The One bookends conceptualization and allows it to progress from some point and terminate at some point. But the “generalization” we depart from is not continuous with the conceptualizations that it gives rise to, neither is the “particular” we converge on. The scare quotes are to recognize that being is neither general nor particular, and there is an important sense in which nothing is in such categories.
2.) Being is most known to us, both because it is whatever is concrete taken in its concreteness, and whatever could be intelligible and therefore abstract. Man is a mind-body or soul-matter composite, but such a being would be a contradiction if the concrete and abstract had no nexus in reality.
3.) Critical philosophy cannot be an attempt to bracket possible knowables, since being is known and it cannot be bracketed. We have a chance at a critical philosophy from a claim about what sort of concepts cannot be linked together, since concepts need to be capable of being conduits from being to being, form the “general” or the “particular”.
4.) The Phaedo account of causality gives a crucial role of abstractions/ things in themselves in causing the concrete or particular actions, e.g. nothing is living except by the presence of life. This leaves open the possibility of further refinement while still insisting that no further refinement eliminates the character of the abstract that causes. We eventually range all actions under the causality of the good, which, like one and being, is beyond both ends of the Porphyrian tree.