The target of the criticisms

The ontological argument is unusual because it tries to prove God's existence from thought rather than observation. Design and cosmological arguments begin from the world: order, purpose, change, contingency, cause. Anselm's ontological argument begins from the concept of God.

For this lesson, the important version is Anselm's. A compact argument chain looks like this:

Gaunilo and Kant attack different pressure points in that chain.

Gaunilo challenges the move from understanding an idea to accepting that the thing exists. He asks whether Anselm's reasoning would prove too much. If the same logic could prove the existence of a perfect island, then something has gone wrong.

Kant challenges a deeper assumption: that existence is a real property or perfection that can be included in a concept. If existence does not add anything to what a thing is, then defining God as supremely great cannot by itself make God real.

This matters for AQA because students need both AO1 and AO2. AO1 is the accurate explanation: who criticises what, and why. AO2 is the judgement: whether the criticism successfully weakens the ontological argument as a proof, while still recognising that a believer might value the argument as faith seeking understanding.

Gaunilo and the lost island

Gaunilo was a monk of Marmoutier and a near-contemporary of Anselm. His criticism is written "on behalf of the fool", meaning on behalf of the person who denies God's existence in Psalm 14. That title matters: Gaunilo is not simply mocking belief in God. He is testing whether Anselm has really shown that the atheist or doubter is irrational.

Gaunilo's most famous move is the lost island analogy, often taught as the perfect island objection.

This is a reductio-style criticism. A reductio argues that if an argument leads to an unacceptable result, there must be a fault in the argument. Gaunilo's point is not that a perfect island actually exists. His point is that Anselm's method seems too powerful: it could apparently prove things into existence just by loading greatness into their definitions.

Gaunilo also makes a subtler criticism. He questions whether merely hearing and understanding words gives the mind the relevant object. A person can understand talk of many imaginary or uncertain things without those things existing. So the move from "I understand the idea" to "the object must exist" needs more support.

His criticism can be organised as an AO1 scholar/source card:

Gaunilo's criticism is powerful for students because it is easy to apply: whenever a philosophical argument appears to move from a concept to a real thing, ask whether the same method could prove imaginary cases. If it could, the argument may be unsound.

However, a strong answer should avoid making Gaunilo too simple. He is not saying "islands disprove God." He is saying the island parody exposes a possible flaw in Anselm's reasoning.

Anselm's reply to Gaunilo

Anselm's reply is important because AO2 is not just "Gaunilo disagrees." A good evaluation asks whether Gaunilo's objection really hits Anselm's argument.

Anselm's main response is that God is not like an island. An island is a contingent, limited thing. It could be larger, more fertile, more beautiful, safer, or better located. There is no obvious maximum island, because island-greatness is not a single unlimited property. It is a bundle of changeable features.

God, by contrast, is defined as the greatest conceivable being. For Anselm, this is not one excellent example within a class of similar things. It is the unique being whose non-existence cannot be conceived once the concept is properly understood.

That gives Anselm a reply:

This is the key AO2 bridge: Gaunilo is strongest if Anselm's argument is treated as a simple formula that can be applied to anything excellent. Anselm is stronger if God is genuinely a unique necessary being rather than one object among many possible objects.

The disagreement turns on a precise issue:

Anselm's reply prevents students from treating Gaunilo as an automatic defeat. Gaunilo exposes a danger in the argument's form, but Anselm can respond that the analogy is not close enough. That leaves a sharper question: is the concept of God really special enough to escape the island parody?

Kant and existence

Kant's criticism is more abstract than Gaunilo's, but it is often the more damaging objection. He does not mainly parody the argument. He asks whether Anselm is using the idea of existence correctly.

Anselm's argument appears to treat existence as a greatness-making feature. A being that exists in reality is greater than one that exists only in the understanding. Kant challenges this. For Kant, existence is not a real predicate: it does not add a property to the concept of a thing.

Use the money example carefully. If you think of one hundred possible coins and one hundred real coins, the concept "one hundred coins" has the same content in both cases. The real coins are better for your bank account, but not because the concept contains an extra descriptive property. Reality changes whether the object is instantiated, not what is contained in the concept.

This produces two linked criticisms of Anselm.

First, existence does not make a concept greater. If I describe a triangle, adding "and it exists" does not add a new side, angle or shape-property to the triangle. It only says that something matching the concept is found in reality.

Second, a definition cannot settle whether anything matches the definition. You can define a supremely great being, but the question remains whether reality contains such a being. Kant thinks existence claims cannot be established simply by analysing a concept.

Kant's argument chain:

Kant also challenges the idea that denying God's existence is a contradiction. If someone says, "God is omnipotent but not omnipotent", that is contradictory because the predicate is being both affirmed and denied of the same subject. But if someone says, "God does not exist", they are not accepting the subject and then removing one property from it. They are denying that such a subject is instantiated at all.

This is why Kant is so important for the ontological argument. He tries to block the route from definition to existence at the level of logic. Gaunilo says Anselm's argument proves too much. Kant says the argument misunderstands what existence does.

Comparing the two criticisms

Gaunilo and Kant are both criticisms of the ontological argument, but they do not do the same work.

The strongest use of Gaunilo is not "there is no perfect island, therefore there is no God." That is too shallow. His criticism is stronger when framed like this: if Anselm's reasoning pattern licenses absurd parallel arguments, Anselm must explain why God's case is unique.

The strongest use of Kant is not "Kant disproves God." Kant does not need to show that God does not exist. He only needs to show that the ontological argument fails as a proof. If existence is not a predicate, then Anselm cannot infer real existence from the concept of a perfect or greatest being.

There is also a difference in how each criticism affects religious faith.

A balanced judgement can therefore say: Gaunilo exposes a serious problem in the argument's form, but Anselm has a reply based on God's uniqueness. Kant is harder to answer because he attacks the concept-to-existence move itself. However, even Kant's criticism does not settle whether God exists; it concerns whether this a priori argument proves it.

Using the criticisms in a paragraph

This lesson is a building block for later AQA-style writing. You do not need to write a full essay here. You do need to know how accurate AO1 becomes evaluative AO2.

AO1-to-AO2 bridge:

Paragraph clinic:

A polished evaluative sentence might be:

Gaunilo weakens Anselm by showing that the argument risks proving too much, but Anselm's necessary-being reply limits the island analogy; Kant therefore gives the deeper criticism because he denies that existence is the kind of property Anselm needs it to be.

Synoptic links should stay restrained. This lesson links naturally to the previous Anselm lesson because it evaluates the ontological argument directly. It also links to the later proof, faith and reason lesson because Gaunilo and Kant help decide whether arguments for God should be treated as strict proofs or as rational support for belief.