The Modal Ontological Argument

[raikou]

But multiple universes are entirely extraneous to this sort of argument. I’ve bolded the important premise: that God is possible because his existence is consistent. If that premise is true*, then there is no reason to aver to multiple universes. The nature of possibility is such that, if it is possible that a necessary being exists, then that necessary being exists. It doesn’t have to exist in some concrete universe or other.

Again, the difference between multiple universes and possible worlds is important. There is not an accepted interpretation of possible worlds semantics. Plantinga takes a Platonist interpretation (possible worlds “exist” in an abstract Platonic “third realm”, while our world is the actual world). David Lewis is famous for his modal realism, in that he thought that each possible world was an actual, concrete universe, and that all possibilities are actual. Most contemporary philosophers, I think, would accept neither of them. A multiple universe hypothesis is not necessarily like either of those. One could take it that way, but just because there are infinite universes doesn’t mean, for instance, that all possibilities are actualized (ie. there doesn’t have to be an alternate universe in which yesterday you joined the circus, although there might be a “possible world” in which that occurred).

*This is the question, though. A lot of philosophical arguments are based on the idea that consistent conceivability implies possibility. (For example, arguments for substance dualism based on the separability of the mind and the body.) But generally such a principle needs restrictions.

I think that in many cases our modal intuitions are simply not up to par, and we do not know enough about the “overflow necessities” of our language. A couple examples for the former and the latter:

a). Consider the laws of physics and of nature. We lack a completed physics, so we do not know how they all tie together, if they do, and in what way. We don’t know which of them could have been different (although we might have some ideas, in some places). We don’t know what would account for their being different, either. So can I say that there is a possible world with some different physical constants? I don’t know. Maybe.

b). Rubies are made of aluminum oxide. We have not known this forever. At times, rubies have been confused with other semiprecious gems like topaz. What we have meant by the word ruby was a substance made of aluminum oxide. But we did not have a sufficient theory of chemistry to realize that until recently. That rubies are a variety of aluminum oxide has always been a “necessity” (in the logical sense) that “overflowed” our linguistic usage of the term. If someone said, “In some possible world, rubies are made of quartz” the statement would have been false, although it did not entail a known contradiction.

I think these are good reasons for modal conservatism.

Oooh. So you mean to say there are three definitions crucial here:

1. necessary - something that ought to exist always
2. possible - something that would have existed at some point
3. consistently conceivable - something that may exist because it has no inherent contradictions (ex. Not a “square circle”)

In that case, the theory I described is that suggesting that all “consistently conceivable” beings are “possible.”

 

[polytropos]

Oooh. So you mean to say there are three definitions crucial here:

1. necessary - something that ought to exist always
2. possible - something that would have existed at some point
3. consistently conceivable - something that may exist because it has no inherent contradictions (ex. Not a “square circle”)

Basically, yes. These aren’t exclusive. Everything that is actual is possible. Much of what is actual is consistently conceivable (but quantum mechanics, say, probably would not have been regarded as consistently conceivable prior to its discovery). Anything that is necessary is possible. Etc.

I would clarify a couple other points. You are formulating the modal terms as temporal terms, ie. “always,” “at some point.” This is not the way they are used by contemporary philosophers. They apply to possible worlds. Something which exists necessarily exists in all possible worlds. Something which exists possibly exists in at least one possible world. Something which exists contingently exists in at least one possible world, and does not exist in some other possible world. They do not clearly translate into temporal terms.

They also don’t exactly translate into metaphysical terms, which is one issue with modal ontological arguments. For something to be necessary does not imply that it ought to exist in all possible worlds, but that it does exist in all possible worlds. We don’t know if it’s in its nature to exist as such, or whether it happens that it is (say) consequent upon some other necessary truth.

Some modal arguments do account for this, for instance James Ross’s Scotist argument defended in his book Philosophical Theology.

In that case, the theory I described is that suggesting that all “consistently conceivable” beings are “possible.”

That is what you were describing. However, I don’t think that premise is true. I think restricted conceivability premises can be true, for some things that are conceivable are possible, ie. it is conceivable that I should go to the store today. But other things are not; particularly conceivability does not so well when it makes assertions about the natures of things which overflow our language and our present knowledge.

 

[empther]

Having an infinite past just means that something has no beginning in terms of duration. God has an infinite past/has no beginning. So what is your problem with an infinite past?

The world changes. Every change is an event. Every event happened a finite time ago.
God has not existed in an infinite past. He is eternal and outside time.

It is possible that God had been causing the universe’s existence for all eternity.

It’s not possible. Eternity is not a period of time.

 

[DanAl]

The Modal Ontological argument is one of the best arguments for the existence of God, but few use it, because they don’t understand it.
The argument uses the concept of possible worlds; a possible world is basically a set of things that could have been true; they are logically coherent and don’t violate any necessary truths, like a law of logic. The actual world is a possible world in which all of these entities and truths are Plantinga’s original argument can seem like he’s making a lot of leaps, so I’ll use another form of it (that I made up) to illustrate how it isn’t a logical leap:
P1: An entity with the property of necessity cannot exist contingently, because that would be a contradiction in terms
Basically, there are three “modalities” (why this is called the Modal Ontological Argument), that can modify the logical possibility of something existing or not existing:
Impossible: An entity that exists in no possible worlds (like a square circle; it is a contradiction in terms, and is thus logically coherent, and can’t exist in any possible worlds)
Contingent: An entity that exists in some possible worlds, but not others (like us;
To be continued

I like the family of modal arguments and they seem terribly underrated by Catholics. I blame Aquinas for this since he “refuted” (if he did indeed refuted it at all) a weak non-modal version of it that has led many Catholics to think that** all** ontological arguments are invalid.

Plantinga’s argument isn’t flawless. One of the premises is that God is maximally good, and by good he means morally good (he’s under certain moral obligations, like humans) which might be rejected by classical theists.

There are some ambiguities as well: is omnipotence logical omnipotence or causal omnipotence (meaning that God can only do what laws of nature allow him to do)? And omniscience, does it mean that God knows what might possibly and what will happen? Does he know counter-factuals?

How would Planting know some of these attributes and not others are pure-perfections only through apriori grounds?

What about divine simplicity? this is no small point, since many theists claim that divine simplicity is essential for God being first in the universe: if God is composed of parts, then the parts are more fundamental than God. God would not be absolutely first if his parts are more fundamental than himself.

But Plantinga’s argument suffers from a weakness shared by all ontological arguments: conceivability does not necessarily entail real possibility. Just because something seems possible to us it does not guarantee that it is possible in reality.

None of these points refute ontological arguments or Plantinga’s version. It is still strong evidence for theism, just not a sure proof of God’s existence.