Posted: Apr 24, 2011 1:44 pm
by Teuton
Paul Almond wrote:
Teuton wrote:Necessary existence is not the same as necessary truth, is it?

They seem very close to me. … The two seem to go together to me, so it seems to me that saying "X exists necessarily" and saying "The proposition that X exists is necessarily true" are equivalent to each other. That suggests to me that necessary existence just corresponds to a particular statement of necessary truth, and necessary existence is just a special case of necessary truth, stated differently.

Yes, as far as logical necessity is concerned, there is an equivalence:

<x exists necessarily> <–> <<x exists> is necessarily true>

But I side with those who hold that there is nothing x that satifies this equivalence: logically necessary existents are logically impossible existents, in the sense that there can be no proposition of the form <x exists> or <the X exists> such that its negation is self-contradictory. Therefore, if "exists necessarily" is taken to mean "exists logically necessary", then it is a logically necessary truth that nothing exists logically necessarily, i.e. then there is no possible world in which something exists logically necessarily.
So "exists necessarily" must be interpreted differently. One suggestion is that it be read as "exists metaphysically/ontologically necessarily". The nontrivial problem with this is that the concept of metaphysical/ontological modality is pretty vague. Even Craig admits this:

"Since metaphysical modality is so much woollier a notion than strict logical modality, there may not be the sort of clean, decisive markers of what is possible or impossible that consistency in first-order logic affords for strict logical modality. Arguments for metaphysical possibility or impossibility typically rely upon intuitions and conceivability arguments, which are obviously much less certain guides than strict logical consistency or inconsistency. The poorly defined nature of metaphysical modality cuts both ways dialectically: on the one hand, arguments for the metaphysical impossibility of some state of affairs will be much more subjective than arguments concerning strict logical impossibility; on the other hand, such arguments cannot be refuted by facile observations to the effect that such states of affairs have not been demonstrated to be strictly logically inconsistent."

(Craig, William Lane, and James D. Sinclair. "The Kalam Cosmological Argument." In The Blackwell Companion to Natural Theology, edited by William Lane Craig and J. P. Moreland, 101-201. Malden, MA: Wiley-Blackwell, 2009. p. 106)

The only clear and precise definition I know interprets metaphysically/ontologically necessary existence as a de re necessity, in the sense that it concerns the essence of things. Of course, "exists necessarily" must not be read as "has the property of existence essentially", since everything existent exists essentially: there is no possible world where there is something that exists without existing. So in order to avoid its trivialization, "is necessarily existent" must be interpreted differently: Necessary existence is essentially eternal existence.

An existentially or, as Richard Swinburne says, factually necessary existent is an essentially eternal existent:

x is an existentially/ontologically necessary being
x is essentially eternal/exists essentially eternally
For all possible worlds w, if x exists in w, then there is neither a first nor a last moment of x's existence, i.e. then x has always existed in w and will always exist in w, i.e. then x is both uncreatable and indestructible in w.

But an existentially/factually necessary existent is a logically contingent existent that does not exist in all possible worlds! So if an existentially/factually necessary, i.e. essentially eternal, god exists, then his existentially/factually necessary, i.e. essentially eternal, existence is "the ultimate brute fact", where a brute fact is an inexplicable logically contingent fact.

"To say that 'God exists' is necessary is, I believe, to say that the existence of God is a brute fact that is inexplicable—not in the sense that we do not know its explanation, but in the sense that it does not have one. …[A]ny terminus to explanation of things logically contingent must be itself something logically contingent. …[T]here are two ways in which God's existence being an inexplicable brute fact can be spelt out. The first position is to say that God's essence is an eternal essence. God is a being of a kind such that if he exists at any time he exists at all times; his existence at all remains the one logically contingent fact. The alternative position is to say that the divine essence is a temporal essence; the ultimate brute fact is not God's existing as such, but his existing for a period of time without beginning. His subsequent existence would be due to his intentional choice at each moment of time to continue to exist subsequently. Theism has traditionally taken the former position, … . In that case God will have the strongest kind of necessity compatible with his being a logically contingent being. Such necessary existence we may term factually necessary existence (in contrast to logically necessary existence)."

(Swinburne, Richard. The Existence of God. 2nd ed. Oxford: Oxford University Press, 2004. p. 96)