I think it is nonsense to say that two things can be semantically equivalent and mean two very different things. Clark Kent and Super Man are either semantically equivalent or they mean different things. Not both, and what matters is precisely what is meant by both.
However, in the case of the MOA, the *only* thing they can be meant by <>G is something that is equivalent to G. Indeed, were this not the case, the argument would not be sound.
Indeed, it is trivial (as I already explained) that one *does in fact* need to affirm God's existence in order to be justified in claiming <>G. There is, by definition, no sufficient support for <>G other than a demonstration that G actually does exist in every possible world. Every other argument would fall well short of constituting justification for <>G.
You are right that circular arguments are not necessarily problematic--thry can be used, as the four first premises in my argument are, to show that several different terms are equivalent.
But the MOA does not do that. It's conclusion is not that <>G and G and []G are equivalent. That is true, as I have proven, and if that were actually the conclusion to the MOA, I would have no problem with the MOA at all.
But it isn't.
The MOA concludes with G.
And it does so by leveraging both the fact that G and <>G are equivalent and the fact that <>G *looks* (to the audience who does not understand the meaning of the meaning of <> and MGB) SS though it bears a lesser burden--that it is easier to justify, epistemically, or can be justified epistemically by different means than, G.
But this is at best incompetent and at worse deeply dishonest.
<>G and G require exactly the same sort of justification, because, by definition, one must be justified in asserting G in order to be justified in asserting <>G, and one must be justified in asserting <>G in order to be justified in asserting G.
This, of course, is because (as we have proven) G is a necessary condition for <>G and <>G is a necessary condition for G.
<>G and G require exactly the same sort of justification, because, by definition, one must be justified in asserting G in order to be justified in asserting <>G, and one must be justified in asserting <>G in order to be justified in asserting G.
This, of course, is because (as we have proven) G is a necessary condition for <>G and <>G is a necessary condition for G.
Here, you confuse a metaphysical fact with an epistemic matter.
Just stating that
x1. if G is a necessary condition for <>G and <>G is a necessary condition for G then for any x , x can only have the same epistemic justification for both
x2. G is a necessary condition for <>G and <>G is a necessary condition for G
x3. for any x , x can only have the same justification for both
1st of all what is to say that G is a necessary condition for <>G and viceversa (what makes x 2 true?) and why is x1 has to be the case?if at all.
Just like in my example of Clark and Superman. What is epistemically required to justify and know 1.Clark Kent is with Louise at Niagar falls is not necessarily the same that is required to Know 3 nor 2, in my example.
1. Clark Kent is with louise at niagara falls
2. Clark is superman (Clark Kent exists iff Superman exists.Clark is with Louis iff Superman is with Louise)
3. Superman is with louise at niagara falls
To beg the question Louise needs to believe 1 or 2 because she believes 3.
S1.Support for 1. Louis Lane is with Clark at niagara falls on an assignment.
S2. Sport for 2. when Louis went at Niagara Falls with Clark he felt onto fire and did not burn, and his eyeglasses fell(his wonderful disguise), at all, and, after all he looks like superman.
She does not believes 1 because she believes 3, nor believes 2 because she believes 3
~S3. Sadly, afterwards Louise got a defeater for 2 since Clark Kent did not give up his facade and tried to save her when she jumped into the falls.
S1 and S2 are different from S3 and from each other.
One can formulate the MOA as follows
P1. If it is possible that God(MGB) exists , then, God(MGB) exists
P2. it is possible that God(MGB) exists
P3. God(MGB) exists.
SM1. The support for P1, is basically the 5 axiom of modal system S5, made explicit in Plantinga´s MOA formulation
SM2. And P2 can be supported by several resrouces provided by the epistemology of modality independent of P1 and P3, like modal intuitions based on conceivability, or understanding, and, other considerations like explaining necessary moroal truths , or mathematical truths, etc...
SM3, could be the Leibnizian cosmologial argument, for example, the direct experience of God.
Neither is P1 asserted because one already knows or asserts P3
Nor is P2 asseted because one already knows or asserts P3.
SM1 , SM2, SM3 are not necessarily the same.