Norman Malcolm's Ontological Argument

This argument for me at first glance, was perhaps the most easy to read, and understand. Simply due to the fact that unlike Descartes and Anselm's arguments there is no confusing definition of God to wrap my head around. Furthermore, because he was using parts of Anselm's Proslogian to form his argument (chapters 2 + 3), it could be assumed that he also thought of God as that than which nothing greater can be conceived. However, because he, like Kant saw error within chapter 2 of Anselm's Proslogian, he sought to use chapter 3, which he established as a second ontological argument which was not susceptible to such criticism as a way to form his own argument.

So, on to his argument, which is as follows;

1) If God does not exist, his existence is impossible
2) If God does exist, then his existence is necessary
3) God's existence is either impossible or necessary
4) God's existence is not impossible
5) Therefore God's existence is necessary

Now, from this argument a few things can be identified, the first thing being that because of the implicitly assumed definition of God, Malcolm therefore states that God is immutable or unchanging. This means that God couldn't and wouldn't change from non-existence to existence, because as he says 'If God does not exist, his existence is impossible'. Another key point about this argument is how Malcolm gives an example of the only thing that is truly impossible, which is the statement "Nothing Exists" as this is an oxymoron, or a contradiction. And so secondly due to this, a further thing that this argument shows is that because of that oxymoron, this next statement "God Exists" can be possibly true and is therefore why he says that the existence of God is not impossible.
Thirdly and finally, another side that can be drawn from his argument, is that of the four possibilities concerning God, which are;

1) Necessarily false - God can't exist.  (any statement that were to fall under this are contradictory propositions, such as the statement 'this square is round)

2) Contingently false - Could but doesn't exist.
(the reasons that 2 and 3 cannot be applied to God are simply because God shouldn't be limited or dependant upon anything else)
3) Contingently true - Could and does exist.

4) Necessarily true - Has to exist. 

So overall, the reason why God is being proved to exist in Malcolm's argument is because God cannot be brought into existence, or be made to stop existing, therefore necessitating God's own existence. And in addition to this because the existence of God is not impossible, it means that there is a chance of this necessary God existing.

It's Anselm not Anslem, and definitely not Aslan.... Anselm's Ontological Argument version 1 + 2

Fides Quarens Intellectum. Anselm was a man of faith, and wrote from a position of faith. Through this Faith Seeking Understanding he would have been writing to put across his Ontological Argument to other people of faith. And this possibly is the most important factor to remember about the argument, as he was starting from the Christian understanding of what the definition of God is. Something that Anselm sought to do with his argument was challenge the fool, who is written about in Psalms 14:1 and 53:1. In both instances it says "The fool says to himself" "there is no God".

Now the first thing to understand is the definition of God that Anselm uses for this ontological argument. For him, God is that than which nothing greater can be conceived (TTWNGCBC). So seeing as this was what Anselm's idea of God was, this also applied to what the Fools idea of God was. So in saying "there is no God" it would seem that the Fool has somewhat contradicted himself in the eyes of Anselm. Indeed as Anselm continues to explain, both existing in reality and in concept is far greater than just existing in concept alone. Which therefore follows that existence of any kind is a great attribute. And as God is that than which nothing greater can be conceived he must therefore fulfil his own definition of being the greatest by existing in both reality and in concept. So, going back to the Fool, it would seem that because he has an idea of God, he is presumably in understanding of the definition of God along with his idea. This is due to the fact that he cannot imagine something and then contest the idea without sharing the same definitions. So because he has an idea of God, by definition this God must exist, for as Anselm explains, God is that than which nothing greater can be conceived.                                                                Which means God exists!

However... Gaunilo had a different idea... For he gave an argument against Anselm's by giving the idea of replacing God with the an island of your dreams, or if you like, that than which no greater island can be conceived. And he seemed to prove Anselm's argument wrong for a while as he correctly said that just because he can imagine a perfect island does not mean that it will exist in reality. As well as this, Gaunilo also stated that "An object can hardly or never be conceived according to the word alone" as the word corresponds to an idea, and while the word may stay the same the idea behind it can be changed endlessly.

BUT! Anselm wasn't so easily proved wrong and came back with a more refined argument. In addition to that, he also reminded Gaunilo that anything that you apply to the island is going to be contingent, as they are all Earthly features, as opposed to attributes of God which are necessary, and cannot ever be understood fully by people. So in order for Anselm to refine it, he asked the question, which is greater; A God who can be though of as not existing? Or, A God who cannot be thought of as not existing? His answer was the second question, because it presents an idea of a God where it is impossible for God not to exist. Furthermore, not only is the second question a description of a greater God, but again a description of a necessary God, therefore proving Gods existence as necessary.