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  • Writer's pictureAndrew Alam-Nist

A Critique of Anselm's Ontological Argument

Editor's Note: In this essay, in a somewhat different tone to some of my other blog posts, I decided that it would be interesting to write in the format of an academic philosophy paper. I have always wanted to write in a more complex and detailed way than I typically get to at school.


I Intro


The Ontological argument is perhaps the most discussed argument in the history of philosophical thought. Its main interest comes not from its power to convince, but rather its unconvincingness. It provokes a negative reaction for nearly all secular believers, and immediate rejection, and yet it is difficult to vocalise the issues with it or demonstrate any clear error within it. This essay explains the ontological argument and then evaluates both the validity of its argumentation and Gaunilo’s rebuttal.


II. Anselm’s Dual Formulations of the ontological argument


Anselm had two main formulations of the ontological argument. The first, which he describes in Proslogium, can be laid out as follows:

  1. It is a truth by definition that God is a being than which none greater can be.

  2. God exists as an idea in the mind.

  3. A being that exists both as an idea in the mind and in reality is, other things being equal, greater than a being that exists only as an idea in the mind.

  4. Thus, if God exists only as an idea in the mind, then we can imagine something that is greater than God (that is, the greatest possible being that does exist).

  5. But we cannot imagine something that is greater than God, by definition

  6. Therefore, God exists.


Within Proslogium, Anselm also laid out a second formulation of the ontological argument, which he created later in his life. This formulation relied upon necessity and contingency and broadly took in criticisms and further thought on the original ontological argument. It can be laid out as follows:


  1. By definition, God is a being than which none greater can be imagined.

  2. A being that necessarily exists, in reality, is greater than a being that does not necessarily exist.

  3. Thus, by definition, if God exists as an idea in the mind but does not necessarily exist in reality, then we can imagine something that is greater than God.

  4. But we cannot imagine something that is greater than God.

  5. Thus, if God exists in the mind as an idea, then God necessarily exists in reality.

  6. God exists in the mind as an idea.

  7. Therefore, God necessarily exists in reality.


The two formulations of the ontological argument have many strong similarities. They are both analytical, basing their argumentation on the definition of God as that than which no greater can be imagined, to logically prove based on the definition of God that existence and necessary existence within reality must be attributes of God.


They are similarly both deductive. If we are to accept their foundational premises and agree with how they are applied, the ontological argument serves as proof of the existence of God.


Both ontological arguments are often considered a priori within the broad philosophical community. This was certainly believed by Anselm himself. This essay disputes this view, however. For an argument to truly be a priori, it needs to be based on knowledge or reasoning which occurs before experience. Whilst there are numerous potential quibbles to be had about nothing being a priori due to language being rooted in experience, this essay posits that neither argument can be a priori due to the premise that something necessarily existing or existing both in both in the mind and the real world being superior to merely existing in the mind.


Both formulations of the argument essentially argue that God’s existence is based on the general idea that existence is superior to non-existence, which is not an a priori claim. There is nothing intrinsic about existence that makes it superior to non-existence. From a purely detached rationally positivist state, existence would indeed not be considered ‘great’. We deem existence to be superior based on our experiences of existence. We think a real cake is better than a theoretical cake due to preferring to eat the cake, which is based on experiences. The reasoning underlying the claim that it is great for God to exist in the real world or to necessarily exist is therefore based on a posteriori reasoning, not a priori reasoning as is typically assumed.


Therefore, we can determine that both formulations of the ontological argument are analytical, deductive and a posteriori.


III. Gaunilo’s Response to the Ontological Argument


The logic of the ontological argument is open to several criticisms. Perhaps the most famous critique comes from Gaunilo, a fellow Benedictine monk and contemporary of Anselm. He uses the example of an island to highlight the absurdity of the conclusions reached by the ontological argument’s logic. His argument can be laid out as follows:


  1. They say that island X (the most perfect island) exists.

  2. If X does not exist, it would be less perfect than any island you care to mention.

  3. Therefore, island X exists.


Gaunilo accepts that the conclusion reached above is quite absurd. It is almost certainly not true that a perfect island exists, so the logic above is likely erroneous. His argument quite well illustrates the error of the first ontological argument but is less effective at tackling the second formulation. The second formulation of the ontological argument would theoretically prove that God is necessary, while any island would be contingent. However, a simple reformulation of Gaunilo’s argument to be worded more similarly to the second formulation, as laid out below, equally rebuts it as well. For the example below, I choose to use a perfect teacher at Westminster because islands are boring.


  1. By definition, a perfect teacher at Westminster is a Westminster teacher than which none greater can be imagined.

  2. A being that necessarily exists, in reality, is greater than a being that does not necessarily exist.

  3. Thus, by definition, if the perfect teacher at Westminster exists as an idea in the mind but does not necessarily exist in reality, then we can imagine the teacher which is greater than the perfect teacher at Westminster.

  4. But we cannot imagine something that is greater than the perfect teacher at Westminster.

  5. Thus, if the perfect Westminster teacher exists in the mind as an idea, then the perfect Westminster teacher necessarily exists in reality.

  6. The perfect Westminster teacher exists in the mind as an idea.

  7. Therefore, the perfect Westminster teacher necessarily exists in reality.


This argument laid out above is equally applicable to the second iteration of the ontological argument and would seem to prove that the perfect Westminster teacher exists. However, despite the greatness of some of my teachers, regretfully we can empirically determine that the greatest Westminster teacher in fact does not exist. Whilst Anselm would say this argument does not stand as teachers, islands and everything other than God exists contingently, he does not truly provide an adequate reason to back up his assertion. His evidence for such a claim is limited to his ontological reasoning which, as outlined above applies to nearly all perfect forms of a thing, not singularly God.


Alvin Plantinga argues again against this type of argument by suggesting that an island has no intrinsic maximum, and therefore has no clearly definable attributes. However, it is difficult to see why God has any clearly definable attributes either. Whilst Plantinga suggests the predicates of the ‘greatest being conceivable’ are obvious, there is little reason to think this is the case. The attribute of ‘greatness’ is a fundamentally subjective term and does not prescribe any concrete characteristics. We can only guess the attributes of a perfectly great God, which is much the same as my conceptual perfect teacher (I would like a teacher who is good at teaching, organised etc…) Therefore, there is no clear difference between the analogy provided by Gaunilo’s argument and the general argument for God provided by the ontological argument and Plantinga’s criticism does not hold up.


Therefore, Gaunilo’s critique of Anselm’s ontological argument exemplifies the erroneous logic which he uses. It does not prove that it is wrong, as it does not challenge any of the premises, which is necessary to disprove an analytical argument. It does however flag that there likely is an error within Anselm’s reasoning which further rebuttals can expand upon.


IV. Other criticisms of the ontological argument


There are several further issues with the ontological argument. As was quite famously argued by Kant, existence is likely not a predicate, as it fails to concretely tell us anything about an object. When I describe an object, its existence would not be an actual attribute that can be assigned to it. When describing my chair, I could say it is wood, tall, white, comfortable and expensive but I would not say it exists, as existence is not a characteristic. This critique of the ontological argument is a quite effective rebuttal of the first formulation of the ontological argument, but not the second. Whilst existence is not a property, ‘Necessary existence’ as prescribed in the second formulation of the ontological argument likely is a property. Therefore, Kant’s rebuttal based on existence not being a predicate is only partially successful.


This essay posits however that the most import rebuttal to the ontological argument lies in Anselm’s characterisation of the first premise:

1- By definition, God is a being than which none greater can be imagined.


Initially, this premise seems to be quite unobjectionable. Atheist and Christians alike would agree that God, if he were to exist would be a perfect being and that than which no greater could exist. However, the statement is errant due to the ambiguity of the word ‘is’. Due to the ambiguity of is, the above premise actually could be interpreted as two different premises:


Premise A: God, if they were to exist, would exist as that than which no greater can be imagined.

Premise B: God exists as that than which no greater can be imagined.


This can be exemplified through the analogy of a unicorn. If I say a unicorn is a horse with a horn, I do not mean that unicorns exist. I simply demonstrate that if unicorns were to exist, they would be horses with horns. It would be a logical error to suggest that unicorns exist based upon the statement.


Similarly, it is an error to suggest that the theoretical characteristic of God defined in premise A necessitates existence. It merely states that if God were to exist, he would exist necessarily.


If one accepts the second interpretation that God exists, then the argument becomes circular, as it defines existence as a predicate. A circular argument fails to provide any new knowledge or prove its conclusion, as its conclusion has to be assumed to make it valid. Therefore, Premise B is equally invalid for proving the existence of God.


Therefore, once the ambiguity of the word ‘is’ is cleared, the ontological argument does not provide any clear logical proof that God exists.


VI. Conclusion


Anselm’s ontological argument is extremely enticing. Close to a millennium after it was conceived, it is still widely discussed by philosophers due to the difficulty to rebut it. It, unfortunately, does not stand up logically, however. Gaunilo flags, with his example of his perfect island, that Anselm’s ontological argument can be used to ‘prove’ several outlandish and empirically false propositions. Kant highlights the issue with defining existence as a predicate, essentially entirely eliminating the first formulation of the ontological argument. However, it is the linguistic error of logic within the ambiguity of the word ‘is’ which ultimately renders the ontological argument insufficient to prove the existence of God.


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