A Critique of Alvin Plantinga's "Possible Worlds" Version of the Ontological Argument

A Critique of Alvin Plantinga’s “Possible Worlds” Version

Of The Ontological Argument

By Forrest W. Schultz


Philosopher Alvin Plantinga has composed an intriguing version of the Ontological Argument which involves the conception of other possible worlds.* Before I set forth and critique Plantinga’s argument, let me first express my praise for what he says in his prolegomenon to the argument. He rightly says there that since God’s attributes are not accidental and adventitious, but intrinsic and necessary, that therefore He would have these same unsurpassably excellent qualities in all the possible worlds He could create, not just this one. This is a very important point, which is rarely mentioned in theology, and Plantinga deserves to be applauded for noting and stressing it. It means that the attributes of God which are revealed in His Word and displayed in His creation are truly His, which means they would be operative in any other possible world He has created, will create, or could create. For example, we must not suppose that God just happens to act righteously in our world but that He might act wickedly in some other world. In short, since God’s aseity means that His attributes are only dependent upon Himself (and are in no way dependent upon anything outside Himself), this means that God would be the same – i.e. unsurpassable great and perfect – with respect to any possible worlds. This can be referred to as the “trans-worlds unsurpassable greatness principle”.

However, it is logically fallacious to try to use this trans-worlds unsurpassable greatness principle to prove the existence of God, as Plantinga does, because this involves proceeding backwards, i.e. moving in thought from the principle to God instead of from God to the principle. The main premises in Plantinga’s argument is his assumption that there is a possible world having an unsurpassably great being. Then, using the principle noted, he says that for this being to be unsurpassable great it must be so in every possible world (including this one). Therefore, it exists.



-1-










It is easy to refute this argument on Van Tillian grounds. First of all, the correct definition of a possible world is a world which would be possible for God to create. Therefore, in order to properly conceive of a possible world we must presuppose God, because it is God who defines what is possible, namely what it is possible for Him to do. Now we must either use this correct definition of possible or else make up our own definition. If we do the former, we need to presuppose God, which means we are begging the question, i.e. assuming what we claim to be proving. If we wish to avoid begging the question by ignoring God then our own definition of possibility would be false, and therefore not usable in any argument.

The way in which Plantinga phrases his main premises makes it clear that he is simply making an assumption, which he hopes the reader will regard as reasonable. But if we do not accept God’s definition of possibility, then each person is free to formulate his own conception of possibility, and according to some of these conceptions the idea of an unsurpassably great being might not be regarded as reasonable. To any such the argument will not be convincing. Plantinga himself recognizes this point and concedes that his argument will not convince everyone.

But the main thing that is wrong with Plantinga’s argument is that he does not treat God as God, i.e. as the Supreme Authority for defining what is possible. Although he wants to convince the reader of theism, in which God is autonomous, he argues on the basis of humanism, in which man is autonomous, and therefore free to judge what he regards as possible. If we claim to be believers in theism, then we should act and think like theists, not like humanists!

NOTE

*Alvin Plantinga, The Nature of Necessity (Oxford University Press, 1974), pp. 213-221



Forrest W. Schultz has a B.S. in Chemical Engineering degree from Drexel University and a Th.M. in Systematic Theology degree from Westminster Theological Seminary.



-2-