Luckily, John Scottus Eriugena wanted very much to deal with that very question. Not, of course, whether God existed or not but rather whether, or to what extent, he (and everything else) could truly be said to be. The distinction appears to have been largely lost in modern times, for we now use the terms 'exists' and 'has being' to mean one and the same thing. For the purposes of illustration, we'll use the same term for reality 1 that Eriugena does, which is physis or natura (nature). For us, that which has being exists in nature. That which does not exist has no being, and is not a part of nature in any way. For Eriugena nature contains all that exists, both that which can and cannot be said to have being. Being and non-being are relative terms, and can be interpreted in different ways, or modes, depending on the circumstances of the discussion, such that being can be both be said to be greater than non-being, and less... 2
Perhaps I am mistaken in trying to link the modern term 'reality' with Eriugena's 'nature', but it serves a purpose, namely to show that his notion of being and non-being is fundamentally different from modern understanding 3 of the terms, and deserves to be pursued further.
In the present paper, however, we shall be content to trace some of the historical background and sources pertaining to Eriugena's great work, Periphyseon or The Division of Nature, and document, as best we can, his meontology - the study of non-being - as discussed in the opening chapters of Book I.
But what was, exactly, the difference between the two, Latin and Greek? From Plato to Augustine their philosophical lineage is identical, and Augustine himself has been described as being "as much a part of the Eastern Legacy as he is of the West." 6 While it is an inevitable simplification, the problem can neatly be summed up for our purposes by two words: negative theology. In short, is being the most fundamental term to apply to God, or is God beyond all being, in which case it might be more true to think of God as superessential non-being. 7 The Latin church held the position that the former was true, while Eastern tradition (and the Pseudo-Dionysius in particular) was keen on the latter evaluation, with all the interesting speculative possibilities that allowed. Eriugena thoroughly embraced this negative theology as expounded by the Pseudo-Dionysius - indeed expanding it to include the realm of created being as well - and if that was to cause his more reactionary readers serious anxiety, it was also responsible for a goodly quantity of highly original thought on his part, so on balance it was probably worth it.
And, conversely, those things which are beyond the grasp of the mind, of which God is foremost, are said not to be. In this mode non-being is clearly superior, or higher, to being, a concept directly adopted from Greek negative theology. 12 In the same section Eriugena goes on to recognise the Western understanding of non-being as privation, or absence, of being. His answer is that either these privations or absences are not part of nature 13, or if they are, their being is somehow associated or attached to the things of which they are the absences and privations of. Either way, they are not to be considered non-being as defined by this mode.
Since God is totally beyond human understanding, he is said not to be. But that, somehow, seems to limit the Divine nature. Eriugena prefers to further distance God from the limitations of both being and non-being, and quotes the Pseudo-Dionysius: "The being of all things is Superbeing, Divinity." 15
Referring then not to God but to His creations, Eriugena assigns being to these creatures in accordance with their perceived place in the hierarchy or order of things, 'from the highest angel down to the lowest part of a rational or irrational soul.' 16
Every order of rational and intellectual creature is said to have and not to have being. It has being insofar as it is known by higher creatures or by itself; it lacks being insofar as it does not allow itself to be comprehended by its inferiors. 17
The novel twist taken here is to reverse the normal neoplatonic approach to the hierarchy of creation, where the higher is a cause of the lower, and thus said to have greater being, all the way up to God, the Supreme Being. The higher, John Scottus says, has no being at all, at least when perceived, if that's the word, by a creature less than itself.
Being and non-being here are relative terms, depending as they do on the difference between subject and mind, rather than any absolute property in the subject itself. Angels have non-being when they are understood by man, but consist of being as they understand themselves.
Eriugena took the negative theology of Dionysius and extended it to include all creation. It was a bold and radical departure from either Western or Eastern tradition. 18
For whatever of the causes themselves is known by generation in time and place in formed matter is said, by human convention, to have being. 20
Those things that are still hidden 'in the innermost recesses of nature' 21 are said not to be. This is not the same as the first mode, where cause and effect are considered as one, as here the effect is said to have being, while the cause is non-being.
The fourth mode states that 'according to the plausible theory of philosophers' 22 only those things 'grasped by the intellect alone' 23 can truly be said to be, as opposed those things which are merely accessible through sense perception. Eriugena gives this mode scant attention, but he appears to be saying that the material world is not, while ideas present in the mind do have being.
Later on in the book, he makes use of a sixth mode, where God is said to be possessed of all being, and creatures are mere nothingness. 26 This is the opposite of the third mode, which gives to the lowest creature the most being.
But ultimately, so what? Being and non-being aren't physical quantities you can sum up and compare, but modes of thought which are useful for meditation on metaphysical problems. As such, one mode makes no logical demands of any other.
Non-being is an intriguing term. The depth and complexity of the issue has hopefully been adequately demonstrated. It is interesting that, on reflection, most people still instinctively take the Augustinian view of non-being, as being a privation, or lack of being. John Scottus Eriugena makes a good case against that simplistic view, and his ideas, in my opinion, deserve further attention.