Time was when the Islamic world could boast world-class philosophers. The Persian Ibn Sina (980-1037 anno domini) was one of them. He is known in the West as Avicenna. Translated into Latin, his works had a major influence on the philosophy of the 12th and 13th centuries and beyond. De Ente et Essentia of Thomas Aquinas is a well-known text that shows the Persian's influence. In this entry I will discuss some of Avicenna's positions in metaphysics as I understand them. My understanding is based on close study of Etienne Gilson, Being and Some Philosophers, and Frederick D. Wilhelmsen, The Paradoxical Structure of Existence. Comments and corrections solicited. That Avicenna anticipates Alexius von Meinong is an idea I arrived at independently. (The exposition of this anticipation belongs in a separate post.)
1) Wilhelmsen credits Avicenna with raising a new question in philosophy: "How is existence related to the order of nature or essence?" (PSE, 40; cf. BSP, 40 ff.) What motivates the new question is the conviction that the world of beings is a world of creatures that owe their existence to a creator. If the Being or existence (esse) of a being (ens) is its being-created-and-sustained-by-God, then there must be a real distinction (distinctio realis) between existence and essence in the creature. To exist is then not to be the same (Plato) or to be a substance (Aristotle). An existing thing is thus in some way 'composed' of essence and existence. Avicenna thus upholds a real distinction between essence and existence. (Is he the first to do so in the history of philosophy? I'm really asking!) I myself understand the distinctio realis along the following lines. (Someone who knows Avicenna's texts can comment on how closely my understanding, which is fairly close to that of Aquinas, matches Avicenna's.)
About anything whatsoever, including God, we can ask two different questions: What is it? (Quid sit?) and Is it? (An sit?) In a contingent being (ens), the distinction between what the thing is (wide essence, quiddity) and its existence (esse) is real, meaning that the distinction pertains to the thing (res) itself apart from our modes of considering it. 'Real' in this context does NOT mean that in a contingent existent such as my cat Max Black there are two things, one res being the essence, the other res being the existence. That is supposedly what Giles of Rome held, not what Aquinas or I hold. I am going to assume that Avicenna did not anticipate Giles of Rome.
Analogy: my head and my eyeglasses are really distinct in the Giles-of-Rome way: head and glasses can each exist on its own apart from the other. But the convexity and concavity of a particular lens cannot exist on their own apart from each other. And yet the convexity-concavity distinction is real, not projected by us. The real distinction that I espouse is like the distinction between the particular convexity and the particular concavity in a particular lens. 'Like,' not 'the same as.' The real distinction between essence and existence in a contingent being such as an optical lens is sui generis: there is no adequate model for it. We acquire some understanding of the sui generis distinction only by analogy from mundane examples.
2) A second Avicennian innovation is a distinction between modes of Being (esse) or modes of existence, different ways for an item to be or exist. (That there are different ways of existing or different modes of Being is a notion fiercely resisted by most contemporary analytic philosophers, but I am of the opinion that the MOB doctrine — to give it a cute name — can be plausibly defended quite apart from Avicenna's particular views. See Holes and Their Mode of Being and the entries in my modes of being category. See also "Existence: Two Dogmas of Analysis" in Novotny and Novak, eds., in Neo-Aristotelian Perspectives in Metaphysics, Routledge 2014, pp. 45-75. One of the dogmas of analysis is that there are no modes of being.) The second innovation presupposes the first, the real distinction. The latter allows us to focus on the existence of the thing without conflating it with its essence or quiddity. We find this conflation in Aristotle for whom there is no difference between an F and an existing F, a man and an existing man, say. For Aristotle, then, there is no difference between Milo and existing Milo. Once one grasps the difference between the existence/existing of Milo and Milo, one can go on to ask how something like Milo exists, in what specific way he exists. In the case of God and Socrates we surely want to say that God exists necessarily whereas Socrates exists contingently. Now it is not obvious, but it can be plausibly argued that this modal-logical difference — typically spelled out nowadays in analytic precincts by saying that God exists in all possible worlds whereas Socrates exists in some but not all possible worlds — is rooted in an ontological difference between two ways (modes) of existing. If that is right, then it is not the case that God and Socrates exist in the same way, pace such luminaries as Alvin Plantinga and Peter van Inwagen and their numerous acolytes. (See my A Paradigm Theory of Existence, Kluwer Philosophical Studies Series #89, 2002, Chapter One, Section 4, "Contingency and Necessity as Modes of Existence," p. 22 f.) Back to the Persian.
3) For Avicenna, there are two modes of existence; there are two ways for one and the same essence/nature to exist/be. The one way is universally in mente; the other is singularly in re. Thus one and the same essence (humanity) exists singularly in the man, Milo, and in the man Socrates, and so on, and universally in the mind of anyone who knows Milo or Socrates or any man to be a man. The first mode could be called esse reale, the second esse intentionale. So if essence is really distinct from existence, then essence is really distinct both from intramental (esse intentionale) existence and extramental existence (esse reale).
4) Given (3), it follows that an essence in itself is neither mental nor extramental, neither universal (repeatable) nor singular (unrepeatable), neither one nor many, neither abstract nor concrete, neither predicable nor impredicable, and — mirabile dictu — neither existent nor nonexistent. The essence in itself is thus a third item, a tertium quid. (It looks very much like a Meinongian Sosein jenseits von Sein und Nichtsein! But Meinong goes on the 'back burner' for now.)
In sum, there are two ways for an Avicennian essence or nature to exist: either in things outside the mind, or else in the mind, and one way for an essence to be (not exist), and that is to be absolutely or indifferently, or if you prefer, amphibiously (either on the dry land of the real, or in the water of mind). It is here that the dialectic becomes tricky and 'aporetic.' For what I take Avicenna to be saying is that the essence or nature absolutely considered, i.e., considered in its neutrality or indifference to both intramental and extramental existence, is in itself a non-existing mind-independent item. That is to say: the essence an sich, the essence as a modally indifferent tertium quid, is not an artifact or product of our considering. Its absoluteness and indifference does not derive from our absolute considering; our considering is an absolute considering because that which is being considered IS (not exists) absolutely. Get it?
Now to exist is to be actual, whether in minds or in things. So the essence or nature in itself which exists neither in minds nor in things, is metaphysically prior to actuality and is therefore a pure possibility. "It follows that pure nature is pure possibility for being in some order. Therefore the possible is prior to the actual in an absolute sense." (Wilhelmsen, 41) Gilson puts it like this: in Avicenna's world, "essences always remain, in themselves, pure possibles, and no wonder, since the very essence of essence is possibility." (BSP, 82)
5) It follows from (4) that essentia as pure possibility is no longer internally tied to esse as etymology would suggest inasmuch as essences in themselves are what they are whether or not they exist in either of the two modes in which they exist. Avicenna thus drives a wedge between essence and existence in such a way that existence can only accede to essences and is insofar forth only accidental to them. Existence 'happens' to them while they on their part remain indifferent to existence.
6) You will recall that for Aristotle, accidents receive their being from (primary) substances (prote ousiai) and are nothing without them. Thus if A is an Aristotelian accident, then A cannot exist apart from some substance or other, and indeed cannot exist apart from the very substance S of which it happens to be the accident. The Islamic thinker takes the Greek's substance-accident distinction and puts it to use in a highly creative way. Whereas accidents for Aristotle derive their being from the substances of which they are the accidents, the Being (esse) of creatures is reduced by Avicenna to an accident of essences which, in themselves, as pure possibles, are beyond existence and nonexistence.
7) (6) entails interesting consequences for the notion of divine creation. On an Avicennian scheme, creation is actualization of the merely possible. If so, God does not create ex nihilo, but ex possibilitate. He doesn't create out of nothing; he creates out of possibles. This does not comport well with divine sovereignty. If God is sovereign, he is sovereign over all orders, including the order of the merely possible. On the Avicennian scheme God is constrained by the ontologically prior order of mere possibles. He is therefore not free. Or at least he is no free in the libertarian sense of 'free.'
8) We have landed in a curious dialectical predicament. On the one hand, we need the real distinction to make sense of divine creation ex nihilo. The pagan philosophers didn't have it or need it, because their systems were not informed by divine revelation. Aristotle's God is not a creator but merely a prime mover. His primary substances exist just in virtue of being the substances they are. For Aristotle, for a primary substance S of kind K to exist is just for S to be a member of K. For Socrates to exist is just for Socrates to be a man. Hence there is no need for a real distinction between Socrates and his existence. On the other hand, the Avicennian scheme, which needs the real distinction, fails to safeguard the absolute sovereignty and freedom of God and fails to capture the radicality of creatio ex nihilo. The reason, again, is that Avicenna's God creates, not out of nothing, but out of possibilities. He is thus not a creator in the strict sense, but a mere actualizer of mere possibles that ARE independently of his will. (Cf. BSP, 83)
