Arguments for the existence of God - The Ontological Argument


Key features of the Ontological Argument

  • Ontos means 'existence' in Greek, so the Ontological Argument is based on the claim that God's existence can be deduced from his definition (a priori).
  • Deductive: it relys upon logical deduction, not sensory experience.
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Anselm's first argument

  • Anselm defined God as 'that than which no greater can be conceived.'
  • There are things that can only exist in our imagination, or there are things that can also exist in reality.
  • Things that exist in reality are always greater than those that exist only in our minds, for example, a painter has an idea in his mind of what he wants to paint; but when he has painted it, this idea is better because it now exists both in his mind and in reality.
  • If God existed only in our mind, He wouldn't be the greatest conceivable being because God in reality would be better.
  • Therefore, God must exist.
  • Anselm argued that it was impossible for the fool (atheist)  to deny the existence of God, since to even use the word 'God' had to convey understanding of what it means.
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Anselm's second argument

  • Gaunilo put forward a reductio ad absurdum (argument to absurdity) to show that Anselm's argument is illogical.  Anselm appears to not have minded the criticism, since it gave him the chance to emphasise the second stage of his argument.
  • Gaunilo used the same formal structure as Anselm to prove that a 'perfect lost island' exists: it is possible to concieve the most perfect lost island, it is greater to exist in reality than to exist in the mind, so the most perfect lost island must exist in reality.
  • Anselm refutes Gaunilo's analogy by refering to the existence of 'necessary' and 'contingent' beings: everything that exists on Gaunilo's 'perfect lost island' is contingent - it can or can not exist - for example, a palm tree will one day rot to pieces.
  • In order for an island to be 'that than which no greater can be conceived', it would have to exist necessarily, since a contingent island is less perfect than a necessary one.  This is impossible, as only God posesses necessary existence.
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Criticisms of the Ontological Argument - Kant


  • 'Existence is not a real predicate.'
  • Anselm's mistake was in thinking that existence is something that can be used as a defining characteristic.
  • For example, if a triangle exists, it necessarily has 3 sides - but it could be that no triangle exists at all, because existence is not part of how we define a triangle.
  • If God exists, then, He must possess all the perfect predicates, such as omnipotence, omniscience and necessary existence - but that does not mean He exists.
  • Predicates merely add to the essence of their subjects, they can't be used to prove their existence.
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Criticisms of the Ontological Argument - Aquinas


  • Any attempt to define God would be to limit God.
  • We do not know God's definition, so Anselm must be wrong.
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Criticisms of the Ontological Argument - Hume


  • You cannot take an idea that exists purely in the mind, apply logic to it and conclude that it exists in the external, physical and observable universe.
  • All knowledge comes from the experience of our five senses, and since the Ontological Argument is not of this nature, then it is a failure.
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Criticisms of the Ontological Argument - Russell


  • Existence does not describe anything, it merely indicates the actuality of an object.
  • To say 'cows are brown' and 'cows are brown and exist' is to say the same thing.
  • Their existence is assumed in the first statement, hence existence adds nothing to our understanding of them.
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Criticisms of the Ontological Argument - Gassendi


  • That which does not exist has neither perfection nor imperfection, and that which exists has various perfections.
  • Therefore, existence can only be thought of as a prerequisite for perfection and not a perfection in and of itself.
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Criticisms of the Ontological Argument - Davies


  • Davies criticised this argument by pointing out that it simply suggests a God is possible and not a physical actuality.
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Strengths of the Ontological Argument - Barth


  • Anselm never intended the argument to be proof of God's existence.
  • It was as a result of a religious experience in which God revealed his nature to Anselm as: 'that than which no greater can be conceived'.
  • For those with faith, the Ontological Argument is clearly true, because it is an expression of their faith.
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Strengths of the Ontological Argument - Descartes


  • A perfect being must possess all perfections and existence is a perfection, so a perfect being must exist.
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Strengths of the Ontological Argument

  • The argument's a priori, analytic nature means it is not dependent upon anything we can observe, and since human observation is not always reliable, this is a good thing.
  • With the Ontological Argument, there is no ambiguity - it either succeeds or fails by its logic.
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Strengths of the Ontological Argument

  • God must, by definition, exist.
  • To accept on the one hand that God is 'that than which no greater can be conceived' and then go on to say that God doesn't exist is to make a logical error.
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Strengths of the Ontological Argument

  • The Ontological Argument is a good training ground for learning the difference between a priori and a posteriori arguments, necessary and contingent beings and so on.
  • In other words, it is useful in the art of how to do philosophy.
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Value of the Ontological Argument for faith

  • When the OA is considered alongside other arguments, then the reasons for believing in God are strengthened (cumulative argument).
  • Some insist Anselm's argument has no value for faith because fideists argue faith cannot be tested by rational inquiry, it is independent of reasoning.
  • Anselm himself stated that arguments for God's existence are there to enable believers to understand more about their existing faith, rather than bringing non-believers to God.
  • Pope John Paul II rejects this view by stating that rational thinking and philosophical discourse can make faith in God possible.
  • Anselm's Proslogium is a prayer directed towards the 'fool' (athiest) in Psalms who says there is no God.  If his argument wasn't intended to be a logical proof to convince the athiest, why does he go to so much trouble to demonstrate the proof of his argument?
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Status of the Ontological Argument as a 'proof'

  • Proof = sufficient evidence for the truth of a proposition.
  • In a deductive argument, if the premises are true, then the truth of the conclusion is guaranteed.
  • However, most scholars argue that the Ontological Argument  does not work because Kant's objections defeat it.
  • The Ontological Argument does not have the status of a mathematical proof, for example, that 2 + 2 = 4.  Nobody doubts that 2 + 2 = 4, but lots of people doubt that Anselm's argument is true.
  • Karl Barth claims that for those who believe in God already, this is a deductive argument that amounts to a personal proof
  • It is possible that for those who are undecided about God's existence, the Ontological Argument could offer a sufficient level of proof.
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