The ontological argument is the attempt to prove, simply from an examination of the concept of God, that the being to which that concept would apply must in fact exist.
The ontological argument in major philosophers:
This argument was developed first by St Anselm. It was critized and somewhat ambivalently rejected by Thomas Aquinas. Revived by Descartes, it was accepted by Spinoza and Leibniz, the latter with some qualifications. It was critized and rejected by both Hume and Kant.
The Ontological Argument in St Anselm:
St Anselm formulated the idea of God as that of “something than with nothing greater can be conceived”. He then argued that something that exists in reality must be greater than something that exists in the mind only; so God must exist outside as well as in the mind, for if he existed in the mind only and not in reality he would not be “something than which nothing greater can be conceived”
The Thomist Objection:
Thomas Aquinas seems to allow the basic principle that the proposition “God does not exist” is self contradictory, while distinguishing what is self evident in itself from what may or may not be self-evident to this person or that : “So i maintain that this proposition ‘God exists’ is self eivent in itself, since ots subject and predicate are identical; for, as we shall see later, God is his own existence”.
Aquinas nevertheless proceeds almost at once to insist on a distinction between what exists in reality and what exists only in thought.
In was in virtue of this important distinction that Kant has later rejected the argument as it appeared in Descartes and Leibniz: “A hundred real thalers do not contain the least coin more than a hundred possible thalers … My financial position is, however, affected very differently by a hundred real thalers than it is by the mere concept of them (Critique of Pure Reason).
Contempory followers of Kant urge that existence is not an ordinary predicate in that it is supposed by the categorical attribution of any others. While to say that something exists is to take it for granted that it has many other attributes. Hume said: “But that Caesar, or the angel Gabriel, or any being never existed may be a false proposition, but still is perfectly conceivable and implies no contradiction”.