Arguments based on reason: the ontological argument


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“it is easier to feel convinced that [the Ontological Argument] must be fallacious than it is to find out precisely where the fallacy lies.” – Russell

A priori. The ontological argument is an a priori argument which means it is not based on experience but logic or pure reason. It claims that if we simply try to understand what the concept of God means, we will see that it must exist.

Deductive. This argument is called a deductive argument which means that the truth of its premises logically entails the truth of its conclusion. If the premises are true, the conclusion must be true. It cannot be the case both that the premises are true and yet the conclusion false.

Deductive arguments as proofs. Conclusions reached by deduction are only as certain as the truth of the premises. Deductive arguments show that if the premises are true then the conclusion must be true. However, the question of whether the premises are true is another matter.

St Anselm’s Ontological argument

Anselm refers to Psalm 14:1 ‘the fool says in his heart, ‘there is no god.’ Since the fool can conceive of God as the greatest being, it would be contradictory to think God doesn’t exist since then God wouldn’t be the greatest being. To say there’s no God is simply to misunderstand what the word ‘God’ means. So, a priori reasoning about the meaning of the word ‘God’ can reach the conclusion that God exists.

P1. God is the greatest conceivable being (by definition)
P2. It is greater to exist in reality than the mind alone
P3. God exists in the mind
C1. Therefore, God exists in reality

Anselm uses the analogy of a painter who has an idea of what they will paint in their mind before creating the painting in reality. This is meant to show that there is a difference between an object being in the mind and being in reality.

 An atheist who does not believe God exists in reality still has the idea of God in the understanding (their mind). Anselm argues that since God is that than which nothing greater can be conceived, it is incoherent to think that God exists in the mind alone because then we could conceive of something greater, i.e., that thing also existing in reality. Yet, what we conceived of is the greatest conceivable being and so it must exist in reality, otherwise it would not be the greatest conceivable being.

“that, than which nothing greater can be conceived, cannot exist in the understanding alone: then it can be conceived to exist in reality; which is greater. Therefore, if that, than which nothing greater can be conceived, exists in the understanding alone, the very being, than which nothing greater can be conceived, is one, than which a greater can be conceived. But obviously this is impossible. Hence, there is no doubt that there exists a being, than which nothing greater can be conceived, and it exists both in the understanding and reality.” – Anselm.

To say that God does not exist in reality is to say that the greatest being is not the greatest being. It is self-contradictory.

Whether God is within our understanding

A strength of the ontological argument is that it is based on a theologically and philosophically convincing definition of God. Anselm’s definition of God is carefully designed to avoid the problem of defining something that is beyond our understanding. Anselm presents an analogy. We can’t fully look at the sun but can still see daylight. Similarly, we can’t fully know God but can at least understand that he is the greatest conceivable being.

“If you say that what is not entirely understood is not understood and is not in the understanding: say, then, that since someone is not able to gaze upon the purest light of the sun does not see light that is nothing but sunlight.” – Anselm

Weakness: 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 and that people have different understandings of God.

“Perhaps not everyone who hears this word “God” understands it to signify something than which nothing greater can be thought” – Aquinas.

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.

Gaunilo concludes:

“So much for the assertion that this supreme nature already is in my understanding.” – Gaunilo.

Evaluation defending the ontological argument

However, Gaunilo’s argument is unsuccessful because a full understanding of the greatest conceivable being or of God’s nature is not required for the ontological argument to work.

Peter van Inwagen explains that 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. It is impossible to conceive of anything greater, so 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.

To adapt a figure he uses in his Reply to Gaunilo, if we cannot look directly at the sun, it does not follow that we cannot see daylight. And, in Anselm’s view, our partial grasp of God’s nature is sufficient to show us that the applicability of the name ‘something a greater than which cannot be conceived’ to God is a consequence of that nature.” – Van Inwagen

Evaluation criticizing the ontological argument:

Gaunilo has a point. When we think about the concept of a being greater than anything we could possibly imagine, the idea of that actual being is not in our understanding.

Furthermore, the insights of Apophatic theology show that reasoning about God is impossible. Pseudo-Dionysius argues that God is simply beyond any human concepts that we can understand. God therefore cannot be grasped by the understanding and so cannot be ‘in’ the understanding.

Gaunilo’s ‘lost island’ response to Anselm

Deductive arguments are strong because the only way to attack them is to deny the truth of the premises (soundness). This is stronger than inductive arguments because they can also be attacked by arguing that the conclusion is false even if the premises are true.

Weakness: Gaunilo denies that the ontological argument is actually a valid deductive argument. He attacks inference from the premises of God existing in the mind to the conclusion of God existing in reality (the inference from P3 to C1). Gaunilo argues:

“I have in my understanding all manner of unreal objects” – Gaunilo.

“he who says that this being exists, because otherwise the being which is greater than all will not be greater than all, does not attend strictly enough to what he is saying. For I do not yet say, no, I even deny or doubt that this being is greater than any real object.” – Gaunilo. 

“I should not admit that this being is in my understanding and concept even in the way in which many objects whose real existence is uncertain and doubtful, are in my understanding and concept. For it should be proved first that this being itself really exists somewhere; and then, from the fact that it is greater than all, we shall not hesitate to infer that it also subsists in itself.” – Gaunilo.

Anselm’s argument could succeed in showing that if God exists, then God is the greatest being and even that it subsists in itself, i.e., has necessary existence. However, this is not enough to show that God does exist necessarily.

Gaunilo then illustrates this with the case of a perfect lost island, which is an illustration of a thing whose real existence is ‘uncertain and doubtful’ yet is in his understanding as a concept.

Applying the logic of Anselm’s argument to this island has an absurd result (reductio ad absurdum). It is greater for this island to exist in reality, so it must exist. This would work not just for an island. The greatest or supremely perfect member of every category must exist. This is sometimes called the ‘overload’ objection because it suggests that reality would be overloaded with greatest/perfect things.

Evaluation defending the ontological argument

In response to Gaunilo, Anselm strengthened his argument into a 2nd form.

Something is greater if it doesn’t depend on anything for its existence. An Island by definition is land enclosed by water, so part of the concept of an Island involves a dependence on things such as an ocean or a planet to exist. So, the greatest possible Island will still be contingent, which means that it is not the case that it must exist.

The existence of contingent beings cannot be proven a priori since their existence is not a matter of definition.

There is nothing in the concept of the greatest being that involves dependence however, unlike the Island. So, Anselm can now argue that this is why the argument works for God but not an Island.

Evaluation criticizing the ontological argument

Anselm’s 2nd form of his argument successfully refutes the relevance of the perfect island. A priori arguments cannot prove the existence of contingent things like islands since their existence is not a matter of definition. However, the greatest being is necessary, so its existence can be prove a priori.

However, Anselm arguably failed to respond to Gaunilo’s central contention.

Even if Anselm is right that we cannot conceive of God without existence, that only proves that God is a necessary being, so that if God existed it would be in a special way where God could not cease to exist. 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

Anselm’s argument only succeeds in showing that if God exists, then God exists necessarily. The ontological argument has not shown that God-the-necessary-being does exist.

Kant’s 1st objection & development of Gaunilo’s argument

A priori arguments are strong because they are not based on experience. Experience can be unreliable. For example, we constantly get newer and better evidence. A priori arguments are based on reason alone and so do not have such downsides. The ontological argument is a priori because its premises only involve reasoning about the definition of God.

Weakness: A priori reasoning cannot establish existence. Gaunilo tried to show that Anselm only succeeds in showing that if God exists, then God exists necessarily. The ontological argument has not shown that God-the-necessary-being does exist.

Kant developed this type of objection. Anselm argues God must exist in order to be God. Kant notes this treats ‘existence’ as a predicate, a description. Kant argued that existence being a predicate of God does not establish God’s existence in reality.

He uses the illustration of a triangle (referencing Descartes’ ontological argument). It is necessary that ‘having three sides’ is part of the concept of a triangle. 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.

We can agree that the ontological argument shows that the concept of God necessarily contains the predicate of existence, but still deny that this necessary being or being greater than which cannot be conceived or maximally great or unlimited being actually exists.

Like Gaunilo, Kant is drawing a distinction between our a priori judgement and reality. A priori reasoning showing that existence is necessary to the definition of a concept in our minds is not the same as showing that concept necessarily existing in reality.

“The unconditioned necessity of judgements is not the same as an absolute necessity of things” – Kant.

“the illusion of this logical necessity has proved so powerful that when one has made a concept a priori of a thing that was set up so that its existence was comprehended within the range of its meaning, one believed one could infer with certainty that because existence necessarily pertains to the object of this concept, i.e., under the condition that I posit this thing as given (existing), its existence can also be posited necessarily” – Kant.

Evaluation defending the ontological argument

Kant’s first critique is unsuccessful because it leads to contradiction. Malcolm objects that if we accept God has the property of necessary existence, we cannot also claim it is possible that God does not exist. Malcolm’s argument is successful because it shows Kant contradicts himself. If God is a necessary being then God must exist. We cannot coherently say God must exist but it is possible that God does not exist.

Furthermore, the analogy between triangles and God fails. A triangle necessarily has three sides but possibly does not exist. A being which necessarily has existence cannot similarly be said to possibly not exist.

When ‘three sides’ is predicated of a triangle, of course we can see how the triangle could not exist. However, when ‘necessary existence’ is predicated of a being, it becomes incoherent to then claim this being possibly does not exist.

Evaluation criticizing the ontological argument

Kant’s first critique is successful because it shows the difference between mental judgement and reality. Our reason can grasp the idea of a being that exists without dependence on anything else. Nonetheless, it is still possible for no such being to exist.

Malcolm tries to object that it’s incoherent to say a necessary being possibly doesn’t exist. The issue is, by necessary he means non-dependent. There is no incoherence in saying a non-dependent being could not exist. God being non-dependent doesn’t show that God must exist, only that if God exists, then God exists without dependence and so cannot cease existing.

Furthermore, Plantinga is the most well-known contemporary defender of the ontological argument. Interestingly, he doesn’t seem to think Kant’s objection can be answered. He accepted that ontological arguments cannot prove that there is a maximally great being, only that if one existed then it must exist. However, he still claims that it’s possible such a being exists. This makes it rational to accept the premise and thus rational to accept the conclusion. So, the ontological argument might show that belief in God is reasonable but cannot prove God exists.

“reformulated versions of St. Anselm’s argument … cannot, perhaps, be said to prove or establish their conclusion. But since it is rational to accept their central premise, they do show that it is rational to accept that conclusion” – Plantinga.

Whether existence is a predicate

Strength: Anselm strengthens his argument in Proslogion chapter 3 to include necessary existence.

In chapter 2 Anselm spoke of existence being greater than non-existence. In chapter 3 he better justifies that premise. Existence is greater than non-existence because a being is greater if it cannot cease existing. A being whose nonexistence is impossible is greater than a being whose non-existence is possible.

If a being can cease to exist, that is because it depends on something else for its existence. Malcolm points out that dependence is a kind of limitation and in common language these concepts are linked to inferiority. A being which doesn’t depend on anything else (is necessary) is therefore unlimited and so is the greatest conceivable being.

This is Anselm’s argument in its strongest form. A being greater than which cannot be conceived must be one whose nonexistence is impossible.

Weakness: Kant’s 2nd objection: existence is not a predicate. 

A predicate is a word that describes a property or feature of a thing. Kant argues existence is not a predicate. To say something exists is not to describe that thing. If I say my cat exists, I do not describe a feature of the cat. I may be describing reality in a general sense, but I am not describing a defining quality of the cat.

Anselm doesn’t explicitly say existence is a predicate, but his argument assumes it. Claiming that God would not be the greatest being (God) without existence treats ‘existence’ as part of what defines God. For Anselm, to say God exists is therefore to describe what God is, i.e., to think existence is a predicate.

Kant’s illustration was 100 thalers (coins). Imagine you have 100 thalers in your mind as a mere concept. Then imagine you also have 100 thalers in existence, not only in the mind. You have two cases of 100 thalers, one which exists in reality and the other which only exists in your mind.

If Anselm was correct that existence is part of the definition of the concept of a thing, then the thalers which exist should be conceptually different to the thalers that do not.

However, the concept 100 thalers is no different whether a mere concept in your mind or instantiated in reality. 100 thalers is just 100 thalers. It has the predicates of shininess, roundness and 100 etc. Being only in the mind doesn’t make the concept somehow less of a complete description of what 100 thalers is. So, existence is not part of the definition of a thing. It is not a predicate or property of the definition of a thing.

Evaluation defending the ontological argument

Malcolm criticised Kant, arguing that Anselm’s second form had been right all along. Kant’s argument worked regarding contingent but not necessary existence. He made the same mistake Gaunilo’s lost island argument made, which was to think we could test the logic of the ontological argument through application to contingent things, such as islands or thalers.

Something is contingent if it is dependent on something else for its existence. The reason for the existence of a contingent thing is therefore external to it and so does not describe or define it. However, a necessary being doesn’t depend on anything else for its existence, so it contains the reason for its existence within itself. Since the reason for its existence is contained within itself, necessary existence must be a defining part of a thing in a way that contingent existence is not. So, necessary existence is a predicate. The ontological argument, which relies on necessary existence, is therefore defended from Kant’s critique.

Evaluation criticizing the ontological argument

Anselm and Malcolm seem correct that necessary existence is a predicate of God. Contingent existence of things like cats and coins is not a predicate, since their reason for existence is something else. However, necessary existence does define and describe a thing.

However, Kant’s first criticism might still succeed:

Even if necessary existence were a predicate of God, that only shows that if God exists, then God necessarily exists. It doesn’t show that God does exist.

Possible exam questions for the Ontological argument

Assess Anselm’s ontological argument
Does the ontological argument justify belief?
Are there logical fallacies in the ontological argument that cannot be overcome?

Can existence be treated as a predicate?
Are Gaunilo’s criticisms of the ontological argument the most effective?
Assess whether Kant or Gaunilo’s critique poses the greater challenge to the ontological argument.

Is a posteriori a more successful form of argument than a priori?
‘A priori argument is stronger than a posteriori’ – Discuss.
Assess Gaunilo’s criticisms of the ontological argument.
Assess Kant’s criticisms of the ontological argument

Quick links

Year 12 philosophy topics:
Plato & Aristotle. Soul, Mind & Body.
Design/Teleological argument. Cosmological argument. Ontological argument.
Religious experience. Problem of evil.

Year 13 philosophy topics:
 Nature & Attributes of God. Religious language. 20th Century philosophy of language.

OCR Ethics
OCR Christianity
OCR essay structure
OCR list of possible exam questions