The existence of God prove that the existence of the transcendental God can be proved deductively by logically deducting the concept of God. Therefore, God must exist so that God can not exist. I think it is necessary to investigate the version of Ansem's ontological debate to answer the question of whether God's existence can be proved a priori.
RenéDescartes, often called the father of modern philosophy, has developed Anselm's assertion when trying to prove the existence of God in the meaning of the word "God". Ontological arguments are a priori arguments. The basis of these arguments depends on the understanding of the essence of the human god. The definition of Anselm's god is "an extremely perfect existence", which is the basis of his argument. God must be something that can not be considered absent: if you imagine a triangle, one of its main features is that it has three sides and three corners. These are triangle predicates. Descartes has expanded his point of view. This time I mentioned the attribute of God. If you imagine something perfect, it must be more perfect if it exists. Also, the most perfect ones have all attributes including existence. Therefore, Descartes believes that a very perfect existence has all the predicates.
Descartes' ontology (or the transcendental theory) is difficult to understand the aspect of his philosophy most appealing. The charm with discussion arises from the effort to prove the existence of God from a simple and powerful assumption. The existence immediately derives from a clear and unique idea of the complete existence. Ironically, the simplicity of discussion also produced some misunderstandings. This is partly because Descartes tends to formalize it in various ways. The main description of this discussion appears in the fifth meditation. This is a question of order and relationship between these two different evidences after the initial causal debate of God in the third meditation. Descartes repeats ontological arguments with other central texts including philosophical principles. He also defended him with the first, second, and fifth reply, against the hard opposition of some famous people of those days.