1. Assess the claim that the ontological argument demonstrates the existence of God. (12 marks)
Clarify the key ideas
Logic
Definition
Premises
Outline opinion
Flawed
Idea
Kant 1 – inseparable predicates
Gaunilo – cannot define something into existence
Argument Against
Anselm – Gaunilo has misunderstood
Counter Argument
Kant 2 – Existence is not a predicate
Conclusion
Argument fails if existence is not a predicate

2. Assess the claim that the ontological argument demonstrates the existence of God. (12 marks)
The ontological argument takes an a priori approach, this is seeking to prove the existence of God based on logic and reason rather than empirical evidence. The argument was developed by Anselm in 1078 who believed that the definition of God as ‘That which nothing greater can be conceived’ proved analytically that God existed.
The premises of the argument can be set out as follows:
Premise 1: God is that which nothing greater can be conceived.
Premise 2: It is better to exist in reality and in understanding than just understanding.
Premise 3: For God to be the greatest thing he must exist in reality and in understanding.
Conclusion: God exists in reality.
I believe that Anselm’s version of the ontological argument is so flawed that it fails to demonstrate the existence of God. 
Anselm argued that part of God being ‘that which nothing greater can be conceived’ included God having the inseparable predicate of necessary existence. Kant criticised this approach by asserting that having an inseparable predicate does not automatically prove that something exists, it only tells us what it would be like if it did, therefore Kant believes we should understand this inseparable predict of necessary existence as ‘if God did exist, he would do so necessarily, and no non-necessarily existing being could be God’.
Gaunilo shared similar objections about defining something into existence and used the argument that just because you can define a perfect island, is does not automatically follow that it actually exists, you would need some other form of evidence to demonstrate this. For many people, these criticisms mean that the argument is not able to demonstrate that God exists. 
Interestingly, Gaunilo voiced his concerns during Anselm’s lifetime and so he was able to respond. Anselm criticised Gaunilo for failing to understand the concept of necessary existence, he believed Gaunilo’s comparison between God and an island to be invalid as islands have contingent existence, they could cease to exist through changes in the water level etc yet God has necessary existence which means that there is nothing that can be done to stop him from existing. Followers of Anselm would therefore refute the claim that his argument fails to demonstrate that God exists.
However, there are further criticisms to the idea that the argument demonstrates the existence of God; part of Anselm’s first premise was the assumption that necessary existence was a predicate of being God, for the argument to succeed this has to be analytically true. Kant believed that it could not possibly be true as existence is not even a real predicate, ‘Existence is clearly not a real predicate’. The function of a predicate is to develop our understanding of something, to give us more information about something and existence fails to do this.
In conclusion, if existence is not a predicate of being the greatest, then it is not analytically true that the greatest conceivable being exists and so the argument fails to demonstrate the existence of God.