The Ontological argument A* grade summary notes


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Anselm’s 1st form of the ontological argument

  • P1. God is a being greater than which none may be conceived 
  • P2. It is greater to exist in reality and the mind than in the mind alone
  • P3. God exists in the mind
  • C1. God exists in reality
  • A priori argument – based on reason, not experience. If you just think carefully about what God is, you’ll see that God must exist.
  • Deductive argument – if the premises are true the conclusion must be true.

Gaunilo’s response: 

  • Replace the word ‘God’ with ‘most perfect/greatest island’ and you get the absurd result that, following P2, this perfect island must exist.
  • This would apply not just to an island, but it suggests there would be a perfect version of everything. 
  • This is sometimes called the ‘overload’ objection, because it suggests that Anselms’s logic means that reality would be overloaded with perfect versions of things.

Anselm responds with 2nd form: 

  • God is a necessary being (does not depend on anything else for its existence) whereas an island is contingent – there’s a difference between them which explain why the logic of the ontological argument works for God but not an island.
  • An island is contingent because it depends on water e.g. a sea. No matter how great/perfect an island is, it still will depends on something else like water. The greatest possible island is contingent, but there’s nothing in the definition of the greatest being that suggests dependence. 
  • If the greatest possible island is contingent, then its existence cannot be a matter of analysing its definition – which is why a priori arguments can’t establish its existence.

Response to Anselm, including Kant

  • Anselm seems to have failed to respond to Gaunilo’s central contention, even if the relevance of the perfect island has been successfully refuted.
  • “I have in my understanding all manner of unreal objects” – Gaunilo
  • Even if Anselm is right that we cannot conceive of God’s non-existence, that does not prove that God does exist. It only proves that we are unable to conceive of God’s non-existence. Gaunilo objects that this is not enough:
  • “in the first place it should be in some way proved that a nature which is higher, that is, greater and better, than all other natures, exists” – Gaunilo
  • This idea of the greatest conceivable and thus inconceivably non-existent being could be one of those unreal objects that is just in our mind.
  • Anselm may be right that our concept of God is necessarily linked to our concept of existence – but this doesn’t actually prove that God does necessarily exist.
  • Gaunilo is suggesting Anselm has failed in his burden of proof.
  • Kant develops this type of objection, arguing that even if existence were a predicate, that could not show that God exists.
  • Kant illustrates the example of a triangle. We can accept that it is necessary that the concept of a triangle has three sides. This shows that if a triangle exists, it must have three sides. Similarly, we could accept that ‘existing with necessity’ is part of the concept of God. Yet again, this only shows that if God exists, then God exists necessarily. It doesn’t show that God does exist necessarily.
  • Even modern proponents on the ontological argument like Plantinga accept that Kant was correct in this criticism and that the most the ontological argument can do is show that if God exists, then God exists necessarily. 

Kant’s 2nd critique: existence is not a predicate

  • A predicate is a word that describes a subject.
  • E.g. ‘black’ is a predicate in the sentence ‘the cat is black’.
  • Anselm treats existence as a predicate. He claims that if God does not exist, then God would not be God – i.e., would not be the greatest being. This is to treat ‘existence’ as a predicate of the word ‘God’. Anselm is thinking of existence as an attribute or quality or characteristic of the concept ‘God’, similar to omnipotence or omniscience.
  • If God wouldn’t be God without existence, then existence is a defining quality of God – it is a predicate.
  • However – Kant argues existence is not a predicate. If successful, this would show that Anselm is wrong to think that God wouldn’t be God if God didn’t exist.
  • Anselm’s ontological argument is saying to say it’s illogical to say God doesn’t exist – it’s just like saying God is not God – the greatest being is not the greatest being.
  • If Kant is right, then God could be the greatest being and yet not exist – since existence is not an attribute of God, without which God would no longer be God (i.e, the greatest being).
  • If I say ‘the cat is black’ – ‘black’ clearly describes a quality of the cat. That’s why it’s a predicate.
  • However, if I say ‘the cat exists’ – it doesn’t look like I’m actually describing a quality of the cat. Existence doesn’t seem to be a predicate.
  • Kant illustrates this point with the examples of 100 thalers. Imagine you have 100 thalers in your mind and also 100 thalers in reality. Kant argues there is no conceptual difference between the two. There is no difference between the one that exists and the one that doesn’t in terms of what it means to be 100 thalers – i.e., the qualities/attributes that it has.
  • 100 thalers is just 100 thalers – it is defined by the attributes of 100, round, shiny, etc. Whether it exists in reality or just as a concept in the mind. There is no conceptual difference between the case where it exists and the case where it does not.
  • In that case, existence cannot be an attribute or quality of the concept of a thing. It cannot be a ‘real’ predicate, therefore.
  • Stating whether something exists describes whether that thing exists, it does not describe a quality that thing possesses.

Malcolm’s critique of Kant

  • Malclom says that Kant was right – but only about contingent existence. Contingent existence is not a predicate – but necessary existence is.
  • A contingent being depends on something else for its existence. This means its reason for existence is external to it and thus not a defining quality of it.
  • A necessary being does not depend on anything else for its existence. This means its reason for existence is internal to it – is a part of it – and thus is a defining quality of it. So Malcolm concludes that necessary existence is a predicate because it does describe a quality of the concept of a thing. He argues that Anselm’s 2nd form was right all along.
  • Cats and Thalers are contingent things! Kant has made the same mistake as Gaunilo when Gaunilo brought up the island example – mistakenly thinking that applying the logic of the ontological argument to contingent things can show it fails to prove the existence of a necessary being.

Gaunilo & Aquinas’ objection: God is beyond our understanding

  • Gaunilo raises an objection to P3; the premise that the greatest conceivable being exists in the mind/understanding, as an idea. Gaunilo draws on traditional Christian theology and claims God is beyond our understanding and therefore cannot be said to be ‘in’ the understanding.
  • We cannot therefore go on to reason about whether it would be greater also in reality. The ontological argument therefore fails because it relies on our ability to understand and reason about things that are beyond our ability to understand or reason about.
  • Aquinas also made this argument against Anselm – that God’s nature, such as the ‘eternal law’ is beyond our understanding.
  • Gaunilo even doubts that we can understand this idea of the greatest conceivable being:
  • “of God, or a being greater than all others, I could not conceive at all”
  • Gaunilo concludes:
  • “So much for the assertion that this supreme nature already is in my understanding.”


  • However, Peter van Inwagen argues that a full understanding of the greatest conceivable being or of God’s nature is not required for the ontological argument to work.
  • Anselm would not accept that we either understand God fully or not at all. Our limited understanding of God’s nature is enough to justify attributing the name ‘that than which nothing greater can be conceived’ to God.
  • God is a being which has traits such as power, knowledge and love yet to their greatest possible degree, i.e., omnipotence, omniscience and omnibenevolence. 
  • We can at least understand that omnipotence involves being able to do any logically possible thing, and omniscience involves knowing every true proposition. 
  • Since it is impossible to conceive of anything with greater power or knowledge than that, we can understand that God is the greatest conceivable being. 
  • We can then follow Anselm’s reasoning that, since it is greater to exist, the greatest conceivable being, i.e., God, must exist.
  • So, the ontological argument is compatible with and not undermined by the fact that God is beyond our understanding.