Descartes claimed "God exists" is true, if we know what it means to talk of God. Similarly, he maintained that once we know what a triangle is we know that it must have three sides. Like a triangle inherently must have three sides, so God inherently must exist.
Objections to the ontological argument were first brought up by a monk who was a contemporary of Anselm named Gaunilo. He said that according to Anselm's line of reasoning, if he envisioned an island that is beautiful and sparkling and completely perfect, then it must exist. For an island that does exist would be more perfect than one that does not exist. Gaunilo said that we cannot simply define things into existence. We cannot show an island or God exists simply by analyzing that idea.
A critique of Descartes comes from the philosopher David Hume who argued against the ontological argument for the belief in God. He pointed out that whatever could be imagined as existing can also be imagined as not existing. He said all statements made about the existence of things can be either true or not true, and must be examined in reality as to whether they are or not. Similarly, Kant said that the ontological argument was invalid because one cannot be going around making a list of attributes and adding existence to the attributes, in order to bring it into reality. Kant claimed that when we have specified something, we must go outside that specification to determine if that thing actually exists.
Descartes and Anselm responded to these challenges. Anselm said that God was an exception to the rule. In his reply to Gaunilo he said "If any man shall devise anything existing in reality or in concept alone except that than which a greater cannot be conceived to which he can adapt the sequence of my reasoning, I will discover that thing, and will give him his lost island never to be lost again." Since only God has every and all perfections, the argument only applies to God. The Psalmist in Psalms 14:1 says that "The fool has said there is no God." Descartes and Anselm thought that this verse referred to one who says, "God does not exist," since only a fool would say that, because they would not know what it means to speak of God. This would be like someone saying that a triangle does not have three sides. That person just doesn't know what it means to speak of triangles.
The concept of understanding God through the ontological argument is a tough idea to grasp, and the debates over it still continue today. This may not be the only (or best) way of showing God to someone, but perhaps this is a view that some people will be able to use to help their justification of belief in God. Unlike the other arguments for God's existence, the ontological argument is an a priori proof. That means that it proves His existence by pure reason. If this argument is shown to be valid, then it is not a matter of probability; God's existence is absolutely certain.
2) ‘The ontological argument fail’s as a theistic proof’. Evaluate the truth in this statement.
Atheists commonly use the "straw god" argument for "proving" God does not exist. They usually claim they argue against the existence of the Christian God, but then demote this "God" to a generic form and argue
against it. Atheists tend to avoid the reality of God revealed from the Bible and science and argue against a finite being.
It is necessary that God is a being that is worth worshipping, so if there is no being worth worshipping there cannot be a God. Not any of the existing religions can provide such a God. If there is a being that has either failed or not tried to communicate with us that being is not worth worshipping either, so the ontological evidence against God holds, even without complete knowledge of the world.
There are several hundred million Christians who believe the Christian God is worth worshipping. However, there are other religions, which worship other Gods. Therefore, this cannot be a valid criterion for determining whether God exists or not.
God both has and continues to communicate with humans. Men with which He has communicated have written His words in the Bible. Those who are born-again Christians communicate with God on a daily basis.
There is a test, based on the ontological evidence against God, that you can do to try the existence of God. Pray, and ask God to provide you with a clear proof for his existence within a week. After that week, if you have got a proof that God exists, then tell people of the evidence. If not, there are only three reasons I can think of that are plausible: (1) God does not exist, (2) God does not want to or (3) God can't give you this evidence. Due to the ontological evidence, alternative (2) and (3) may not be worth your worship and thus they equal alternative (1). So if you get no response there may not be a God.
There are some major problems with the validity of this test, since the Bible tells us this test will fail. The Old Testament tells us not to test God. Jesus reinforced this concept when He was tempted by Satan, who told Him to jump off the temple wall. Jesus cited the same verse from Deuteronomy not to test God. Therefore the only thing this test proves is that God is not the God of some non-Christian religion.
However, there is a test you can do which will give valid results. Jesus said, "For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have eternal life." (John 3:16) "He who has My commandments and keeps them, he it is who loves Me; and he who loves Me shall be loved by My Father, and I will love him, and will disclose Myself to him." (John 14:21) This is the only valid direct test for the Christian God's existence.
The Bible never defines God as infinite, but defines Him as existing beyond the limitations of our four dimensional universe. This does not mean that He is infinite. Some Christians have said that God is infinite, but this concept cannot be supported biblically. The only characteristic of God described as infinite is His knowledge or understanding. Therefore, the argument does not hold, since the God of Christianity is not described as infinite. It is for this reason the ontological argument can fail as a theistic proof however it is not an easy answer to the question as it holds both ‘for’ and ‘against’ reasoning for the theistic proof in the existence of God.