Posted originally by **TheQuestion**

This doesn't make sense. If an entity doesn't exist, it doesn't have a nature.

You're assuming the non-existence of the entity in order to show it is impossible. This would be like objecting to the statement "Squares have four corners" by using the argument "If the square didn't have corners, then it wouldn't have corners."

You are essentially begging the question.

If an entity is said to be metaphysically necessary, de re (by definition)... non-existence cannot be assumed to disprove the argument, because you are assuming the hypothetical to be false in order to prove it is false.

What you CAN do is argue that a metaphysically necessary being is an incoherent idea which defies the laws of logic. That is a difficult case to make, but it is the only other option. In other words, you can argue that that a necessarily existent being is "logically impossible" but you cannot argue that a necessarily existent being may not exist (because that statement is self-contradictory).

Posted originally by **TheQuestion**

No, no they are not. Mathematical axioms are in no respect similiar to the claim that a being exists.

You are right on this. A mathematical axiom (or any axiom, for that matter) is by definition a self-evident truth. You cannot prove an axiom, because an axioms are too fundamentally basic to be proved. Rather axioms are those basic truths which we use to prove everything else.

However, you seem to be arguing that one cannot propose a hypothetical being that is metaphysically necessary, because by defining the being this way we have insured the conclusion of the argument to be that it must exist. But that is not the case.

A hypthetical being that is metaphysically necessary can be proved or disproved using logic. If such a being is logical, then it must exist. If it is illogical, then it cannot exist. However the third option is ruled out, in which such a being is logical and yet does not exist. The definition of the hypothetical being does not allow this conclusion.

The above paragraph is entirely provable using Alvin Platinga's modal axiom S5. The logical possibility of a metaphysically necessary being has not been proved, it is merely assumed for the sake of the argument. But if such a possibility were ever proved, then such a being's reality is logically inescapable. And likewise, if such a being were ever proved to be logically impossible, then the argument fails.

The above explanation proposes a hypothetical, which is then evaluated using established axiomatic proofs, just the same way that any acceptable mathematical theorem would be evaluated using mathematical axioms.

You may suggest reasons why a metaphysically necessary being is illogical, but if it is logically possible, then its existence is confirmed.