2Anselm’s argumentGod is a being ‘greater than which cannot be conceived’If you could think of something that is greater than God, surely this something would be God.Think of two beings, one that exists and one that doesn’tBeing real is greater than being fictional. So the one that actually exists is greater.So if God didn’t exist, we could think of a greater being than God.
3Anselm’s argumentBy definition, God is a being greater than which cannot be conceived.I can conceive of such a being, i.e. the concept is coherent.It is greater to exist than not to exist.Therefore, God must exist.
4Anselm’s argument Think of two almost identical beings, X and Y. X is a being which we can conceive not to existY’s not existing is inconceivableY is greater than X.The greatest conceivable being is a being who, we conceive, must exist.The thought ‘God does not exist’ seems to make sense, but on reflection, we find that it is incoherent.
5Gaunilo’s objection 1 How great is the greatest conceivable being? If it doesn’t exist, it is not great at all!We are thinking how great this being would be if it existedThat doesn’t show that it does exist.
6Gaunilo’s objection 2You could prove anything perfect must exist by this argument!I can conceive of the perfect island, greater than which cannot be conceived.And so such an island must exist, because it would be less great if it didn’t.But this is ridiculous, so the ontological argument must be flawed.
7Anselm’s replyThe thought that the greatest conceivable being doesn’t exist is incoherent. But the thought that the greatest conceivable island doesn’t exist is coherentThere is nothing in the concept of such an island that makes it essentially or necessarily the greatest conceivable island.Compare: it is essentially surrounded by waterInstead, the concept of ‘the greatest conceivable island’ is somewhat incoherent.
8Anselm’s replyGod wouldn’t be God if there was some being even greater than GodBeing the greatest conceivable being is an essential property of God.This, however, doesn’t deal with Gaunilo’s first objection.
9Descartes’ argument‘The idea of God (that is, of a supremely perfect being) is certainly one that I find within me…; and I understand from this idea that it belongs to God’s nature that he always exists.’
10Descartes’ argument I have the idea of God. The idea of God is the idea of a supremely perfect being.A supremely perfect being does not lack any perfection.Existence is a perfection.Therefore, God exists.
11Descartes’ argumentConsider: you can think that there can be triangles whose internal angles don’t add up to 180 degrees. But reflection proves this impossibleOur thought is constrained. Our concepts determine certain truths.You can think that God doesn’t exist. But this is to think that a perfect being lacks a perfectionAnd I can’t change the concept of God any more than the concept of a triangle. I discover it.
12ObjectionThere is a difference between thinking God exists and God actually existing.Reply: but you can infer one from the other (as with the internal angles of triangles)‘from the fact that I can’t think of God except as existing it follows that God and existence are inseparable, which is to say that God really exists’.
13Hume’s objectionNothing that is distinctly conceivable implies a contradiction.Whatever we conceive as existent, we can also conceive as non-existent.Therefore, there is no being whose non-existence implies a contradiction.
14Hume’s objectionIf ‘God does not exist’ is a contradiction, then ‘God exists’ is a relation of ideasBut claims about what exists are matters of fact.If ‘God does not exist’ is a contradiction, then ‘God exists’ must be analyticBut claims about what exists are synthetic.
15Descartes’ responseDescartes could argue that ‘God exists’ is analytic or that it is synthetic, but known a prioriBut he doesn’t have these concepts.Descartes actually says: all divine perfections entail each otherIf God is omnipotent, then God must not depend on anything elseTherefore, God must not depend on anything else to existTherefore, God must have necessary existence.
16Pressing the objection (from Gaunilo) Descartes’ argument only works if God exists, because only if God exists, is God omnipotent, etc.The interdependence of perfections shows only that the concept of existence is part of the concept of GodIf God doesn’t exist, then God isn’t omnipotent (or anything else), so God’s omnipotence doesn’t entail his existence.
17Kant’s objectionBoth Aquinas and Descartes talk of existence as a property, because they think it can make something ‘greater’ or ‘perfect’This is a mistake. Existence is not a property.Suppose ‘God exists’ is an analytic truthAn analytic truth unpacks a concept. The predicate tells you something about the subject.To say ‘x exists’ is not to describe x at all or explain what x is. Existence is not part of the concept of anything.
18Kant’s objectionTo say ‘x exists’ is to say that some real object corresponds to the concept of xThis is a synthetic judgement. So it is not a contradiction to deny it.There is no difference in the concepts of 100 real thalers and 100 possible thalersAdding the concept of something existing does not change the concept.
19Kant’s argumentIf ‘God does not exist’ is a contradiction, then ‘God exists’ is an analytic truth.If ‘God exists’ is an analytic truth, then ‘existence’ is part of the concept of God.Existence is not a predicate, something that can be added on to another concept.Therefore, ‘God exists’ is not an analytic truth.
20Kant’s argumentTherefore, ‘God does not exist’ is not a contradiction.Therefore, we cannot deduce the existence of God from the concept of God.Therefore, ontological arguments cannot prove that God exists.