Plantinga's Possible worlds

Arguments for the Existence of God
by Metacrock - edited by JMT
Used with Permission

Argument XIV, Plantinga's Possible Worlds

Plantinga's Possible World's.

Dr. Forrest Baird, Ph.D. Philosophy, University of Southern Illinois

P1 A thing has maximal greatness if and only if it has maximal excellence in every possible world.

P2 Whatever has maximal excellence is omniscient, omnipotent and morally perfect.

P3 There is a possible world in which the property of possessing maximal greatness is exemplified.

P4 The property of possessing maximal greatness is exemplified in every possible world.

P5 If maximal greatness is exemplified in every world, then it is exemplified in this world.



Plantinga is a leading figure in what is called "analytic philosophy." This type of philosophy represents not so much a particular content as a method of dealing with philosophical problems. The method uses rigorous logical analysis of propositions using a number of rather technical logical concepts.

Like others who use this method, Plantinga's work is difficult to understand without some background in logic. Plantinga uses a system of modal logic that is on the cutting edge and still the topic of much debate. He relies heavily on certain theorems about modal operators that are not universally accepted. Many articles that critique his work are written almost entirely in symbolic logic and so are not accessible to most students.(24) But by first examining some key concepts Plantinga uses, we should be able to make sense of his version of the argument.

Alvin Plantinga
A. Concepts

1) Possible Worlds.



"Plantinga begins his discussion of the ontological argument by borrowing seventeenth century philosopher Leibniz' idea of "possible worlds." A possible world is a possible state of affairs. So, for example, there is a possible world in which I am able to execute dazzling slam dunks and a possible world in which I am lucky to make a basket at all. The second of these, but certainly not the first, is actual or "obtains." But both of these worlds are possible. While the first does not obtain, there is nothing that is logically impossible about it. On the other hand, a world in which I play basketball with a round square is not possible. Such a world not only does not obtain, it could not obtain."(25)

"Turning to the ontological argument, Plantinga rewrites the argument in terms of possible worlds. Instead of using a premise which says that God's existence is possible, Plantinga says that God exists in a possible world. If God's existence is possible, then there must be a possible world in which God exists. Of course that possible world might not be this world--just as the possible world in which I can slam dunk is not this world. But if God's existence is at least logically possible (i.e., the concept of God's existence is not a concept like "round square"), then there is a possible world in which God exists."

2) Possible Beings.


"Immediately after stating that there is a possible world in which God exists, Plantinga makes a revision of this statement. To say "There is a possible world in which God exists" is to talk about God as a possible being. Both Malcolm and Hartshorne had assumed that this makes sense: that one can talk about God as a possible being and discuss the qualities of this possible being. Plantinga questioned this assumption."
B. Properties rather than beings.

"But, Plantinga argues, it does not make sense to speak of merely possible beings, beings that don't in fact exist. We can't say that "X does not exist" leads to the statement "there is an X such that X does not exist." This would be like saying "there is a thing that does not exist." If it does not exist we can't say "there is a thing...." Or, we can't say "there is a thing such that this thing does not exist." Plantinga suggests that we should be talking about properties. Rather than talking about whether a particular being exists, we should talk about the exemplification of certain properties. Is there an instance of this property in a possible world. Baird says:"

"Consider the case of the property of being able to execute dazzling slam dunks. In one possible world (the actual world) that property is exemplified by Michael Jordan (and others). In another possible world (the one of my imagination) that property is exemplified by Forrest Baird. In yet another possible world that property is exemplified by some unidentified being. But in all three cases we are talking about the property of being able to execute dazzling dunk shots. We can ask whether or not that property is exemplified in a particular possible world without talking about the being that exemplifies it."

"By revising the argument in terms of properties, Plantinga makes the argument immune to Kant's criticisms about existence not being a predicate. The argument is no longer talking about a thing that may or may not have certain predicates--including existence. It is now an argument about certain predicates and whether or not there is an instance of them. Plantinga even disagrees with Malcolm and Hartshorne about necessary existence. Plantinga holds that not only is existence not a predicate, neither is necessary existence": As Plantinga Says:"

"...A being has no properties at all and [therefore] no excellent-making properties in a world in which it does not exist. So existence and necessary existence are not themselves perfections, but necessary conditions of perfection."(28) "A being must first exist to have any perfections, so existence, of any type, cannot be one of the perfections a being has."(29)

C. Maximal Greatness.

"Rather than thinking of God in terms of a being, "that which none greater than can be conceived," Plantinga thinks in terms of the property of "maximal greatness" or the property of unsurpassable greatness; none other could possess such a quality for there can only be one such manifestation of this property. If two beings were each "the greatest possible being" which would be greater than the other?"

But Plantinga doesn't talk about a being with this property. Rather, he asks, is the property exemplified in any possible world? Maximal greatness, or Maximal excellence would consist of omniscience, omnipotence and moral perfection, so the question is, is this quality exemplified in any possible world? But this still doesn't mean that this quality is exemplified in our world. In some other possible world the maximal greatness might be petty in our world. But Plantinga argues: "...The greatness of a being in world W [any given possible world] depends not merely upon the qualities it has in W; what it is like in other worlds is also relevant." (in Baird) (32) So greatness is relevant from one world to another. But to have the property of maximal greatness a being would have to be the greatest in all possible worlds.

D. The Point of the Argument.

1) Plantinga's Modal Version of the Argument.

P1 A thing has maximal greatness if and only if it has maximal excellence in every possible world.
P2 Whatever has maximal excellence is omniscient, omnipotent and morally perfect.
P3 There is a possible world in which the property of possessing maximal greatness is exemplified.
P4 The property of possessing maximal greatness is exemplified in every possible world.
P5 If maximal greatness is exemplified in every world, then it is exemplified in this world.

Baird says:

"This argument is valid in its logical structure, but is it sound and persuasive? As mentioned above, to be sound means that the premises must be true and to be persuasive means that most persons would accept the truth of the premises. P1 and P2 are both given as definitions of terms. Plantinga stipulates them as the definitions of the terms he is using.(34) They are, quite literally, true by definition. P4 follows from P1 and P3. Given P1 and P3 there must be some individual (let's call that individual "x") that exists and has maximal excellence in every possible world. No matter what possible world we choose to examine, x would have to have maximal greatness in that world since x possesses maximal excellence in every world. P5 makes the rather obvious point that since our actual world is also a possible world, whatever is true of all possible worlds must be true of this possible world. So P1, P2, P4, and P5 are all true: P1 and P2 by definition and P4 and P5 by logical inference. That leaves only P3".

Plantinga's conclusion:

"What shall we say of this argument? It is certainly valid; given its premises, the conclusion follows. The only question of interest, it seems to me, is whether its main premise--that maximal greatness is possibly instantiated--is true. I think it is true; hence I think this version of the ontological argument is sound." [In Baird](35)

2. The Possibility of God's Existence.

But can he really prove P3? That might require making a whole other proof for a skeptic. However, God's existence is certainly possible in some possible world. Like Hartshorne he argues that if God is possible than he is necessary, or there is no sense in speaking of a merely possible necessary being. If God exists than God's existence cannot be a contingent fact. To question this would be like questioning whether tables are things to put things on. That is what God is, necessary being, and if God is not actually necessary than he is impossible but cannot be merely possible. God is not like other beings who may or may not exist. If my Parents had met different people and been married to them rather than each other I would not be me, but they might or might not have had any children at all. This might have happened, therefore, I might or might not have come to be. My existence is contingent. But God is not like this, he either must exist or else it is impossible that he could exist, but there is no "might or might not" in the equation.

If God might exist in some possible world he must exist in all possible worlds.

E. Objections.

1) Tooley, reverse possible world thinking.

Michael Tooley try's to reverse Plantinga's argument by saying that a statement that is not self contradictory is true in some possible world. So to say "there is no maximally great being" is true in some possible world. The statement "there may be a unicorn" must be true in some possible world because it could be true. But reversing Plantinga's logic, the talk about a maximally great being must apply to all possible worlds and so there cannot be a maximally great being! [this is in Dr. Baird's notes]

Answer: Mark Strasser comes to the rescue in arguing that Plantinga could say that "there is an X" could be true in some possible world unless it is contradictory. If X is the maximally great being. In that case X would have to be true in all possible worlds since a maximally great being could not be merely possible. Both Tooley and Plantinga have concepts that are not self contradictory. Stasser argues that the contradiction test alone is not sufficient to determine the case.

Here is Strasser's test for determining the possible existence in all possible worlds:

1. A is not internally inconsistent, and,
2. A does not entail that A1 exist in all possible worlds, or,
3. if A's existence does entail the necessary existence of A1, then we must establish independently that A1 exists in all possible worlds.(45)

But I suggest that the answer is much simpler than turning some test. The reversal of an ontological argument, which many have attempted, goes back to he work of J.N. Findly in his classic argument with Hartshorne. Hartshorne convinced Findlay that the argument of reversal always leads to a ready inversion, so the OA is on again. I suggest that the principle of ontology always works toward reversing its opposite but doesn't work the other way around. In other words, anytime the OA is reversed it leads back to inversion. But if one reverses Findly or Tooley it does not. This is illustrated as follows:

If we say "There is no maximally great being" in some possible world, this is not true obviously if it is true that there can be such a being in some possible world, because if there is than there must be one in all possible words, since that is what Maximal greatness is; necessary being. IF it is possible for God to exist than God must exist! In other words, "there is no maximally great being" is never a true statement. Tooley's argument is not sound. It would be correct to say, "we don't' know that God actually exists, perhaps God is impossible." But if God is not impossible (because not self contradictory) than it makes no sense to apply the possible world's theory to God's existence in some possible world since for God to be possible is to be necessary in all worlds. NO one could say then that "there is no maximal being in some possible world" because that would be like trying to confine God's necessary existence to some possible world. Trying to impose God's non-existence upon all possible world's through the possibility of it on some possible world is like trying to confine God's existence to just one possible world, it does not make sense.

2) Existence is not a predicate.

This is one of the traditional objections that was assumed to have killed off the original OA when Kant said that existing is not a quality of perfection that can define it's being. So the phrase "that which nothing greater than can be conceived" is not telling us that God actually exists because we do not know that existing is greatness is predicated upon existing. This is discussed on the previous page (unless I decided not to and forgot). But possibility is a predicate of existence. The possible worlds scenario may get around this argument because in this case greatness is not predicated upon existence but upon the possibility of existence, and for that it may well be. Why? Because we have added something to the concept. We are being told something different in this case about the situation. We are being told that not only is this quality one of greatness, but it is one of possible greatness, as opposed to impossible greatness.

By Metacrock. Used with Permission.
For more articles by the same author, see Doxa.