To begin more simply: the expression "beyond being" as ordinarily used in metaphysical discourse is not so very bizarre as to be incomprehensible. In fact it has a perfectly respectable pedigree, going back to Plato, who says of the Form of the Good, at Republic 509b9-10, that it is "beyond being in dignity and power". This may puzzle some at first sight, but it need not generate many worries. Plato's theory of causation is peculiar but, like Berkeley's immaterialism, once you grant a premise here or there the whole thing follows with adamantine unassailability. On his view, the Forms cause particulars to be what they are by means of a vaguely defined relation called "participation" (methexis) and, by virtue of a rather controversial principle known in the literature as self-predication each Form may be predicated of itself (for example, Justice is just, Equality is equal, etc.). The Form of the Good is said to be the aitia (explanatory cause) of the being of everything else. When you combine this fact with participation and self-predication you open the possibility that the Form of the Good is nothing other than Being Itself. But Plato does not want to equate the Good with Being, and this is why he says that the Form of the Good is "beyond being". What he means is simply that the Form of the Good is something other than Being Itself even while it serves as the origin and source of the being of all things that have being.
In one sense it is tempting to say that God, as opposed to the Good, is Being. But clearly he is not Being Itself in a Platonic sense, otherwise he would be identical to his creatures. Instead, God, like the Form of the Good, is the cause of the being of his creatures, but he is not identical to their being. It follows from this either that God and Being are distinct, or that the being of everything that is not God is a different sort of being than is the Being that is identical to God. The traditional way to handle this rather complicated set of relations is very nicely laid out by Dr. Michael Liccione in one of his recent posts on the Filioque. As usual his treatment of the issues involved is so much better than I could have hoped to produce that it will serve my own best interests to remain silent on the topic. Instead I will speculate a little about how this relatively benign problem of Platonic metaphysics has come to infect the division between East and West with regards to the Filioque and the doctrine of Divine Simplicity by means of a bifurcated route consisting of (a) the metaphysics of hypostases and (b) a curious accident of philosophical history.
Platonic metaphysics has had a unique history--I think one would be hard pressed to find any other respectable system of metaphysics that has endured for more than 2300 years--but it is a reticulated and labyrinthine history. This is particularly true if one agrees with such scholars as Harold Tarrant and Lloyd Gerson that Aristotle was a kind of Platonist, albeit a rebellious one. Putting the whole Aristotelianism thing on the back burner for just a moment, however, it's worth jumping forward about 500 years to the time of Plotinus. Plotinus is one of the neglected geniuses of Western philosophical history. Like Aristotle, he can be described as "a kind of Platonist", but precisely what kind is a matter of some controversy. In Ennead 5.8.1 he refers to Plato's doctrine that the Good is "beyond being" in a way that makes you wonder if he read the same texts that we read:
[Plato] teaches, also, that there is an author of the Cause, that is of the Intellectual-Principle, which to him is the Creator who made the Soul, as he tells us in the famous mixing bowl. This author of the causing principle, of the divine mind, is to him the Good, that which transcends the Intellectual-Principle and transcends Being: often too he uses the term 'The Idea' to indicate Being and the Divine Mind. Thus Plato knows the order of generation--from the Good, the Intellectual-Principle; from the Intellectual-Principle, the Soul.Astonishingly, Plotinus says all of this in order to show that his metaphysics are solidly grounded in Plato's own, and represent no serious departure from the teachings of the master. My purpose in quoting this passage, however, is not to make light of Plotinus--who, as I have already said, seems to me to be a genuine genius--but to illustrate the expansion on the concept of methexis, participation, in later Greek philosophy. In Plotinus, participation has morphed into emanation, a process that is about as controversial among scholars of Plotinus as participation is among scholars of Plato. One things seems clear, however. The language of emanation (usually expressed in terms of the verb rhein, "to flow") is remarkably similar to language of either Platonic causation or, even more remarkably, Thomistic creation ex nihilo:
But how is that One the principle of all things? Is it because as principle it keeps them in being, making each one of them to be? Yes, and because it caused them to be (184.108.40.206-9)The One, then, is like the Christian God insofar as it serves both as creator ex nihilo and that which sustains the being of each thing that is. Another interesting feature of the Plotinian One can be made to appear when we consider what Mike Liccione has called God's being "essentialy hypostatic", an idea that seems designed to underwrite the necessity of the relations among the Persons of the Trinity while preserving the Father's unique role as origin and source of all things. If this analysis is correct, it is remarkably similar to the relationship between the One, Intellect, and Soul in Plotinus' metaphysics, in which the One serves as a unique origin and source of all being but to which Intellect and Soul are essentially linked by reflexive relations.
I'm not trying to suggest that we can understand Trinitarian theology better by studying Plotinian or Platonic metaphysics; I'm simply tracing out the history of some metaphysical ideas that are clearly in the same family as the metaphysics behind the doctrine of the Trinity. What complicates things rather drastically in all of this is the role of Aristotelian metaphysics in the history of philosophy. Aristotle was not widely read in the east in the two centuries after his death--Plato was always regarded as the more important philosopher and it was his system that had the most influence in the Hellenistic and post-Hellenistic philosophical movements. By a curious twist, Aristotle's phoenix-like rise from the ashes of history began not in the East but in the West, where the philosophers of the high middle ages came into contact with his ideas through their dialectic with Islamic philosophers, many of whom had written commentaries on Aristotle's logical and metaphysical treatises. These Arabic commentaries were translated into Latin, along with enough Aristotelian texts (translated into Latin not from Greek, which most Western philosophers at the time did not know, but from Arabic) to make sense of the commentaries. As a result, much Western reaction to the philosophy of Aristotle at this time was mediated by the conflict between Christian and Islamic theology.
When St. Thomas began writing his own commentaries on the works of Aristotle, his sources were Latin translations that came from this tradition. It was to be another two hundred years before the Greek texts of Aristotle became widely available in the West, but his philosophical ideas were already widespread when the first Greek refugee scholars began arriving in Vienna and other Italian cities, fleeing from the fall of Constantinople in 1453 and bringing many Greek texts with them that had long been lost to the West. Plato's philosophy, which had dominated the East until the 6th century, was only partially known in the West, where the Timaeus had been widely circulated in a Latin translation due, ultimately, to Cicero, but little else was known. Even St. Anselm, himself a dedicated Platonist, knew very few of Plato's actual writings. His Platonism, like everyone's Aristotelianism, had been filtered through the lenses of Plato's commentators, mostly Neoplatonist in orientation and dating to the 2nd and 3rd centuries.
This is the milieu in which Eastern philosophy was absorbed and incorporated into Western theology. Aristotle's doctrine of causation, while clearly grounded in Platonic precedents, was just as clearly quite different from Plato's. In particular, Aristotle had criticized Plato for neglecting the material cause in his explanatory scheme. St. Thomas, who was more comfortable with the views of Aristotle than those of Plato, clearly incorporates an Aristotelian causal/explanatory scheme in his own writings, where human beings are not pale imitations of some Form of Humanity, but body-soul compounds, metaphysical unities of a sort quite unlike anything Plato ever endorsed. Because the influence of Aristotle was greater than Plato's in the West, and because the West knew relatively little about either of them, the grand tradition of Greek metaphysics underwent a significant metamorphosis in the West, becoming, eventually, the metaphysics of the Schools with which we are now familiar and which bears so little resemblance to genuine Platonism or Aristotelianism, even while the roots of both are clearly evident.
What was happening in the East while this was taking place in the West? Plotinus is just the beginning of the story, representing, as he does, the beginning of the Neoplatonic tradition that was to influence Christianity so strongly. After the fourth century, however, philosophy in the East began to undergo a long, precipitous decline in quality and influence. Whereas in the West philosophy and theology had become partners in the dialectical search for the truth about God, in the East this was strictly the task of theology, and in a culture as dominated by religion as was the Byzantine empire, it was theology that thrived, not philosophy. When, in 529, the emperor Justinian imposed severe restrictions on the teaching of "pagan" philosophy--which, at the time, meant pretty much all of philosophy--it signaled the end of an age of enlightenment that had lasted for over a thousand years. An examination of what passed for philosophy between the death of Justinian in 565 and the death of Byzantium in 1453 leaves little room for admiration. In a review of a recent volume on Byzantine Philosophy and its Ancient Sources (Oxford University Press, 2002), R. J. Hankinson has written:
Ultimately, then, on the basis of this learned collection, my answer to the question posed at the outset (how important is Byzantine philosophy?) would be: in its own right, not very. There is one substantial article I have not yet touched upon (I exclude Linos Benakis’ none the less useful “Epilogue: Current Research in Byzantine Philosophy” from this category): John Duffy’s “The Lonely Mission of Michael Pellos”, which takes its title form Psellos’ own assessment that “I am a lone philosopher in an age without philosophy” (p. 152). He also claimed that “Philosophy, by the time I came upon it . . . had already expired, . . /; but I brought it back to life, all by myself” (p. 155). Duffy comments that “Psellos was no stranger to exaggeration . . . [but] on the issue of philosophy, the evidence suggests that he is telling us nothing but the truth”. To that conclusion, a deflating one for a historian of philosophy at least, I would add that the time of the patient’s coma was a very long one, and that Psellos did not really succeed in resuscitating it. For the most part, the “philosophers” treated in this book are not only unoriginal (that may indeed be a venial sin, if indeed it is a sin at all)—they are uninterestingly unoriginal.Ouch. That's going to leave a mark. It tends to explain, however, how it has come to pass that the brilliant metaphysics of Plato and Plotinus have come to be debased to such an extent that one can no longer get coherent ideas out of their followers. While in the West theology adopted the methods of philosophy and improved upon many of the ideas, in the East it seems that the divorce of philosophy from theology has resulted in an aimless wandering and tinkering to no good result, with people saying things like "God is not a being as such" and not only having no idea what they are talking about but also having no idea of the history behind what they are talking about. I suppose in one sense they have managed to escape Hankinson's criticism: they are not saying something unoriginal, because the original was really something quite different--it actually made sense. Instead, they fall victim to a criticism one often hears of undergraduate papers: what's good is not original, and what is original is no good.