'God is that than which nothing greater can be conceived'
In other words it is better for something to exist in reality that in the mind, or to exist is the best quality something can possess.
For example, it is possible to think of mythical creatures such as dragons and faeries, so therefore, at some time or another, they must have of existed or still may do so, but the main point is because something is conceivable it has to exist, as long as it is relation to God.
The Main Points of 's ontological argument
(1) God is that than which no greater can be conceived.
(2) If God is that than which no greater can be conceived then there is nothing greater than God that can be imagined.
Therefore:
(3) There is nothing greater than God that can be imagined.
(4) If God does not exist then there is something greater than God that can be imagined.
Therefore:
(5) God exists.
The first premise of this argument, (1), is Anselm’s conception of God. (2) is a simple logical truth; if God is the greatest conceivable being then there is no greater conceivable being, (3) follows simply from (1) and (2).
Anselm argues in support of (4) by comparing a non-existent God with an existent God. An existent God, says Anselm, is greater than a non-existent God. If God were non-existent, therefore, then we could imagine a God greater than he, namely an existent God, (5) follows simply from (3) and (4).
Gaunilo’s Criticism
Gaunilo of Marmoutier, a monk and contemporary of Anselm's, is responsible for one of the most important criticisms of Anselm's argument. Anselm's argument illegitimately moves from the existence of an idea to the existence of a thing that corresponds to the idea; Anselm simply defines things into existence-and this cannot be done.
Gaunilo worried about this because with Anselm’s argument one could use it show the existence of all kinds of non-existent things, he highlighted this by saying:
“Now if some one should tell me that there is … an island [than which none greater can be conceived], I should easily understand his words, in which there is no difficulty. But suppose that he went on to say, as if by a logical inference: "You can no longer doubt that this island which is more excellent than all lands exists somewhere, since you have no doubt that it is in your understanding. And since it is more excellent not to be in the understanding alone, but to exist both in the understanding and in reality, for this reason it must exist. For if it does not exist, any land which really exists will be more excellent than it; and so the island understood by you to be more excellent will not be more excellent.”
Simply, Gaunilo was saying just because I can imagine something in my mind does not necessarily mean that it exists, therefore you can picture this perfect island, but because its there in ones mind and there it shall stand until proven.
Anselm retorted by saying that his argument only focused on God, and therefore was only applicable to God, so according to Anselm, Gaunilo’s argument was totally irellevent.
