Anselm's ontological argument assumes that existence is one of God's perfections. If a supremely perfect being didn't exist, then it wouldn't be supremely perfect, which is a contradiction;
ergo, it must exist.
A standard way of criticizing the ontological argument is to claim that the argument rests on a false assumption; that is, it rests on the assumption that existence is a perfection. Kant claimed that existence is not a property at all, the way colors or shapes are properties, but rather an utterly different concept.
Kant's view was accepted by the framers of standard symbolic logic. In standard symbolic logic existence doesn't appear as a property at all; rather, it's a so-called quantifier. So, if one were to try to articulate the ontological argument using standard 20th-century symbolic logic, the articulation would fail because that logic doesn't allow for existence as a property.
I'm sorry, but I think Kant was a hack.
I study philosophy and I find his meditions to be problematic to a huge degree. His categorical imperative merely begs the question of duty or "Good" and never actually defines how there can be a natural law without a lawgiver. He limited his thought because he was working with the presupposition there was no God.
Thats the problem with alot of philosophers is that they arent open to the idea of God. Not that you have to believe in God to be a good philosopher, rather, because they firmly believe there ISNT one, it taints the objectivity of their musings. Descartes was willing to believe in whatever logic allowed, and logic led him to God. He started from nothing and came to have an understanding of the divine.
Kant was convinced there was no God and set out to prove it. He didnt set out to find TRUTH, rather he set out to fortify his own idea of what was true. Thats why he loses alot of credibility. He had an agenda.