Alvin Plantinga is one of the greatest living Christian philosophers. His contributions to philosophy of religion and metaphysics are widely recognized. Plantinga is unconvinced that the ontological argument is unsound and develops his own version of the argument that might well be more powerful than Anselm’s original. What can be confusing about the argument to people who don’t have some previous familiarity with philosophy is the notion of a “possible world.” A possible world is simply a way the world might have been. In other words, a possible world is any state of affairs that is logically possible ( any state of affairs that is not self-contradictory in some way). We’ll summarize the argument briefly:
It is possible that there is a greatest possible being.
Therefore, there is a possible being that in some world or another has a maximum degree of greatness – a degree of greatness that is nowhere exceeded.
A being has the maximum degree of greatness in a given possible world only if it has a maximal degree of greatness in every possible world.
If a being with a maximum degree of greatness exists in every possible world, it exists in every possible world.
If a being exists in every possible world, it exists in the actual world.
Therefore, a being with a maximum degree of greatness exists in the actual world.
Interestingly enough, most of the controversy surrounding this argument is regarding whether a greatest conceivable being is even possible. The rest of the argument is relatively uncontroversial in academic philosophy. Most philosophers think that if God’s existence is possible, he must exist. [i] This argument avoids some of the usual objections to the ontological argument (for example, that existence is a predicate or that existence is a perfection). The most confusing premise to philosophical laymen would probably be premise 3. Why does a being with a maximum degree of greatness in a given possible world need to be maximally great in every possible world? This simply makes the point that a being’s greatness is not simply determined by how it is in its own world but by how it is in other worlds. A being that is morally perfect in one world but would have been malevolent in another world is clearly inferior to a being that is morally good in all possible worlds. A being who is good no matter what is clearly better than a being who is only good under certain circumstances.[ii]Thus, the greatest possible being in one possible world, must be the greatest possible being in every possible world.
Greatest conceivable anything?
It is very common for critics of the argument to contend that the logic of the ontological argument can prove the existence of anything whatsoever, from greatest pizzas, to the worst conceivable being, or the greatest possible island. The problem with most of these objections is that islands or pizzas or other similar objects don’t have an “intrinsic maximum.”[iii] This means that the sorts of properties which would make an island great (such as the number of palm trees and amount of time in the sun) do not have a limit such that a greater number or amount of those properties would not always make it better. Or, “No matter how great an island is,…there could always be a greater…That is, there is no degree of productivity or number of palm trees (or of dancing girls) such that it is [logically] impossible that an island display more of that quality.”[iv]Apart from this, an island or pizza do not have objective great-making properties. How much cheese has to be on a pizza for it to be the greatest conceivable pizza? How many palm trees has to be on an island to make it the greatest conceivable island? These characteristics are subjective. It would be different depending on the person you ask and what their tastes are.
One might say it doesn’t matter that these objects have no intrinsic maximum. There are perhaps scientifically proven or objective measures that would make an island most enjoyable to people. But firstly, this would require the assumption that a great island is simply one that gives the greatest enjoyment to human beings. Why should that be the case? In addition, there will still be a large subjective component. Even if there is some baseline of enjoyment that can be scientifically proven, every person will have their own preferences that make the island most enjoyable to them personally. But then maybe the baseline represents the greatest conceivable island because that is exactly where subjectivity becomes necessary to make it greater. However, if the purpose of the island is for subjective enjoyment, it would not be the greatest conceivable island for most people, because most people would have individual preferences beyond the baseline (which would make them enjoy it more). So such an island would fail to provide the greatest enjoyment to human beings. What about a greatest conceivable human being? There may be some aspects of human beings that are objectively great-making. But how muscular should a human be, or how lean, for them to be the greatest conceivable human being? How physically attractive? Is someone who is physically attractive objectively superior to someone who is less physically attractive (or is this only an issue to potential romantic partners)? How tall? How long should he live? As long as possible or just as long so as to avoid the indignities and suffering of old age? What personality traits should he have? Pretty much the only characteristics of human beings that have an objective great-making quality is morality and belief. That person should believe all true things and do all right actions and no wrong actions. Firstly, these are not enough objective great-making properties, because something can conceivably have these properties (morality and true belief) and not be human. And secondly, there are too many other characteristics that are essential to being human (such as having a human body, having certain personality traits etc.) In short, any physical thing cannot have a greatest conceivable instantiation, because any physical thing does not have properties that have intrinsic maximums or are objectively great-making.
Worst Conceivable Being?
There is also a parody of the argument that follows the logic of the ontological argument but inserts the “worst” instead of “greatest.” Arguably, however, a being is even worse if it does not exist in reality, so it makes no sense to contend that the logic of the ontological argument applies to a worst conceivable being. Perhaps you might say that it would be worst if the being actually existed. But you must answer the question: for whom is it worst? We are not talking about whether the being would be the worst conceivable being for the world or for human beings, but the worst conceivable being in terms of its own properties. The worst conceivable being, in terms of its own properties, would not exist, because a being that doesn’t exist in reality is clearly inferior to one that does exist. Thus, the worst conceivable being cannot exist.
Defining God into Existence?
A common critique of the ontological argument is that it simply defines God into existence. It contends that existence or necessary existence is part of the definition of God and because of that, God exists. This may be true of Rene Descartes’s version of the ontological argument, which I think is the weakest version (and at which Immanuel Kant’s criticisms were originally aimed). However, if you look at Anselm and modern formulations of the ontological argument (such as by Plantinga, Hartshorne and Malcolm) it becomes impossible to maintain this critique. For example, the Anselmian ontological argument clearly doesn’t even define God. In fact, it doesn’t even deal with God. It’s conclusion is simply that the greatest conceivable being exists, and it is a further step to identify this with God. Anselm deals simply with what properties the greatest conceivable being will have and these can be determined objectively. It then looks at the logical implications of a greatest conceivable being (one of them being existence). None of these arguments contain any version of the following reasoning process “By definition, God is an existent being, therefore God exists.” The ontological argument is about what the implications are of a concept of a greatest conceivable being. If that is really what the ontological argument boils down to, then you should be able to use its logic to prove the existence of anything at all. As we’ve already seen ( through the response to the first objection) this is not even close to possible.
[i] William Lane Craig, Reasonable Faith, (Wheaton: Crossway, 2008) 185
[ii] Alvin Plantinga, “A Contemporary Modal Version of the Ontological Argument”, in Philosophy of Religion: Selected Readings ed. Michael Peterson, William Hasker, Bruce Reichenbach and David Basinger, 4th ed. (New York: Oxford University Press, 2010) 180
[iii] Ibid., 176
[iv] Ibid., 176