The medieval Islamic philosopher Ibn Sina orAvicenna (c. 980 - 1037) is one among that myriad of thinkers of genius unjustly neglected by contemporary philosophers. Useful recent studies of his thought include the updated edition of Lenn Goodman’sAvicenna and Jon McGinnis’s Avicenna. More recent still is McGinnis’s essay “The Ultimate Why Question: Avicenna on Why God is Absolutely Necessary” in John F. Wippel, ed.,The Ultimate Why Question: Why Is There Anything at All Rather than Nothing Whatsoever? Among the topics of this essay is Avicenna’s version of the argument from contingency for the existence of a divine Necessary Existent. Let’s take a look.
The argument McGinnis discusses can be found in the Najāt, with the relevant excerpt available in the anthology Classical Arabic Philosophy, edited by McGinnis and David Reisman (at pp. 214-15). The background to the argument is Avicenna’s view that existence, necessity, and possibility are better known to us than anything we could say in order to elucidate them. In particular, the claim that something or other exists is more obviously correct than any argument we could give for the claim would be. And the notions of necessity and possibility are more basic than any other notions we could appeal to in trying to define them. (Note that he is not saying that the existence of something necessary is more obvious than any argument we could give for it; on the contrary, his aim is precisely to give an argument for it. That something or other exists he takes to be evident; and what it would be for a thing to be necessary he takes to be evident. But whether something necessary actually exists he does not say is evident, but requires argument.)
Nevertheless, Avicenna does think that we can say something todescribe the notions of necessity and possibility, even if we cannot strictly define them. He says that something that is “necessary in itself” is something that is entirely determinate in itself and thus requires no cause, so that if it exists it could not fail to exist under any conditions. By contrast, something that is “possible in itself” is something that is inherently indeterminate as to its existence or non-existence, and thus requires a cause. Again, though, these are not definitions in terms of better known or more basic concepts, but rather just criteria for identifying what would count as a possible thing or a necessary thing. (Avicenna also identifies a third category of what is possible in itself but necessary through another. That would be something that of itself need not exist but is nevertheless necessarily caused by some cause.)
So, is there something that exists in a necessary way? That brings us to Avicenna’s argument, of which McGinnis gives an exposition over several pages. What follows is my own outline of McGinnis’s statement of the argument. (McGinnis does not put things in this step-by-step way, so the reader should not assume that he would necessarily agree with every detail of my reconstruction.)
Here, then is the argument:
1. Something exists.
2. Whatever exists is either possible or necessary.
3. If that something which exists is necessary, then there is a necessary existent.
4. Whatever is possible has a cause.
5. So if that something which exists is possible, then it has a cause.
Let’s pause briefly. You might expect that after step (5), Avicenna’s strategy would be to argue that we must rule out an infinite regress of causes. But that is not his approach. Instead he turns his attention to the metaphysical status of the totality of possible things (where the question of whether this totality is infinitely large or not is not in view here). Returning to the argument:
6. The totality of possible things is either necessary in itself or possible in itself.
7. The totality cannot be necessary in itself since it exists only through the existence of its members.
8. So the totality of possible things is possible in itself.
9. So the totality of possible things has a cause.
10. This cause is either internal to the totality or external to it.
11. If it is internal to the totality, then it is either necessary or possible.
12. But it cannot in that case be necessary, because the totality is comprised of possible things.
13. And it also cannot in that case be possible, since as the cause of all possible things it would in that case be its own cause, which would make it necessary and not possible after all, which is a contradiction.
14. So the cause of the totality of possible things is not internal to that totality, but external to it.
15. But if it is outside the totality of possible things, then it is necessary.
16. So there is a necessary existent.
Note that in step (13) the idea of self-causation is raised. Avicenna does not actually think that such a thing is possible, but is merely allowing it for the sake of argument. His point is that if a possible thing were its own cause then it would be entirely determinate in itself and rely on nothing outside it, in which case it would not really be possible but necessary. Since this is a contradiction, what led us to it -- the assumption that the cause of the totality of possible things is internal to the totality and thus itself possible -- must be rejected. Of course, if we simply reject the possibility of self-causation out of hand, the same result follows more quickly.
As McGinnis notes, among the distinctive features of this argument are that it not only does not require a premise to the effect that an actual infinite is impossible (as cosmological arguments often do), but also does not rely on a premise to the effect that the world of possible things is orderly (as a teleological argument does), or that it is in motion (as an Aristotelian argument from motion does), or is multiple as opposed to unified (as a Neoplatonic argument might). Its aim is to show that if anything so much as exists at all then there must be a necessary being.
What should we think of this argument? And what can we know about the nature of this necessary existent?
