Anselm’s ontological argument has been formulated various ways, but for now here is a version from the Stanford Encyclopedia of Philosophy (originally from Plantinga):
- God exists in the understanding but not in reality. (Assumption for reductio)
- Existence in reality is greater than existence in the understanding alone. (Premise)
- A being having all of God’s properties plus existence in reality can be conceived. (Premise)
- A being having all of God’s properties plus existence in reality is greater than God. (From (1) and (2).)
- A being greater than God can be conceived. (From (3) and (4).)
- It is false that a being greater than God can be conceived. (From definition of “God”.)
- Hence, it is false that God exists in the understanding but not in reality. (From (1), (5), (6).)
- God exists in the understanding. (Premise, to which even the Fool agrees.)
- Hence God exists in reality. (From (7), (8).)
One famous way to criticize this argument is through parody. The most well known parody is the one by Gaunilo, a contemporary of Anselm. In short, the parody objection says that by the same reasoning employed in Anselm’s argument, one could prove the existence of all sorts of things we know not to exist, such as a perfect island.
There are two problems with the perfect island parody. First, the island parody is not strictly analogous to Anselm’s argument. To truly parody an argument, it must be strictly analogous and entail an absurdity. Anselm’s argument is about the set of all possible beings, whereas Gaunilo’s objection deals with a subset of that set, namely islands. So, the scope of Gaunilo’s objection is not parallel to that of Anselm’s (Nagasawa 30). Yujin Nagasawa gives an example to demonstrate why this causes the objection to fail:
“Suppose that we construct an argument that is concerned with all possible people. We then construct its parallel parody that is concerned with all possible weightlifters, which, of course, constitute a subset of all possible people. It is far from obvious that the fact that a parallel argument about all possible weight lifters entails an absurd conclusion tells us anything about the plausibility of the original argument about all possible people” (Nagasawa 30).
The second problem with the parody objection is that it makes assumptions to which the defender of Anselm’s argument isn’t committed. The parody’s implicit assumption is that there are intrinsic features of a perfect island that make the island perfect by virtue of having those and only those features (Nagasawa 31). The assumption is implicit in the Anselmian argument insofar as the theist believes there is a set of intrinsic features of God by virtue of which God is the greatest conceivable being, namely maximal great-making properties, such as omnipotence, omniscience, and omnibenevolence. However, this assumption is not strictly analogous to the island assumption due to the reasons given above. Islands are merely a subset of all possible beings, so the analogy doesn’t hold due to a difference in scope. Furthermore, it doesn’t seem obvious that there is a specific number of beaches and trees (and whatever else that makes an island great) that the greatest conceivable island intrinsically has; it seems like for any number of pleasant beaches and trees, one more of each could be added to increase the island’s greatness.
So, Gaunilo’s parody fails by virtue of a disanalogy between the set of all islands and the set of all beings. It makes assumptions about the intrinsic nature of the greatest conceivable island that the defender of Anselm’s argument is not committed to. Also, it isn’t obvious that there is a specific number of features that makes an island greatest conceivable island; rather, there seems to be no upper limit on the number of those features. What is it about any particular number of great making features that makes a particular island the greatest, rather than some other number? There seems to be no way to answer that question.
Nagasawa, Yujin. The Existence of God a Philosophical Introduction. Abingdon, Oxon: Routledge, 2011. Print.
Oppy, Graham, “Ontological Arguments”, The Stanford Encyclopedia of Philosophy (Spring 2015 Edition), Edward N. Zalta (ed.), URL = <http://plato.stanford.edu/archives/spr2015/entries/ontological-arguments/>.