Anselm offers a reduction ad absurdum argument. This is an argument whose denial leads to a contradiction or some other absurdity.
Anselm’s Argument from Proslogian 2 is as follows:
Premise 1: Firstly, we must consider what God is said to be like. Anselm says that “we believe” God to be “that than which nothing greater can be conceived”. In other words, God is the greatest thing that a person can think of.
Premise 2: Even a fool “understands what he hears, and what he understands is in his intellect”. There, Anselm means that even the non-believer has the idea of God as the greatest conceivable being. They must do in order to argue against his existence.
Premise 3: From this, Anselm argues that God does exist, if even in the intellect (in intellectu) of a believer or non-believer.
Premise 4: Anselm then argues that it is greater to exist in both the understanding and reality, than merely in the understanding.
Premise 5: The greatest conceivable being must exist in both the understanding and reality if it is to truly be the greatest.
Premise 6: Therefore, God exists in both reality and in the understanding.
In his work “On Behalf of the Fool”, Gaunilo suggests that using Anselm’s method, we could deduce anything we want into existence, so long as it has superlative qualities such as being the “greatest” or “most excellent”. Gaunilo states:
“For example: it is said somewhere in the ocean is an island … And they say that this island has an inestimable wealth … it is more excellent than all other countries … Now if someone should tell that there is such an island, I should easily understanding his words … But suppose that he went on to say … ‘Since it is more excellent not to be in the understanding alone, but to exist both in the understanding and in reality’, for this reason [the island] must exist.”
In other words:
* We can imagine an island which is the greatest conceivable island.
* It is greater to exist in reality than just in the understanding.
* Therefore, the greatest conceivable island must exist in reality.
Plantinga’s Counter Criticism
An issue arises when we consider the subjects being used by Gaunilo and Anselm. Gaunilo’s example of an island is flawed, as it is a subject that can always be improved upon. However, the subject of God is one that by definition cannot be. Plantinga argues that Gaunilo’s argument only works if we use an idea that has a definite condition of perfection, and because Gaunilo’s island can forever be improved, “the idea of a greatest possible island is an inconsistent idea; it is not possible that there be such a thing.”
Further Reading & Next Steps:
Davies’ Orchid Counter Criticism
Anselm’s Second Ontological Argument (Proslogian 3)
Descartes’ Ontological Argument
Plantinga’s Ontological Argument