The Ontological Argument is Sound

Most philosophers agree that if God’s existence is possible, then he must exist. That is, God's existence is necessary, and necessary existence is a property. A well known and well defended argument is below where steps 2-5 are uncontroversial. The key premise is 1.Ontological Argument1. It is possible that a maximally great being exists.2. If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.3. If a maximally great being exists in some possible world, then it exists in every possible world.4. If a maximally great being exists in every possible world, then it exists in the actual world5. If a maximally great being exists in the actual world, then a maximally great being exists.6. Therefore a maximally great being exists.DefinitionsA Possible World is a Maximal Description of Reality, not planets or a universe. It's just a way reality might be. Imagine a huge conjunction where propositions, p, q, r, s … and worlds, W1, W2, etc:A possible world is a conjunction which comprises every proposition or its contrary. Such a conjunction yields a maximal description of reality—nothing is left out. So by negating different conjuncts in a maximal description of reality would yield different worlds:W1 = p, q, r, s …W2 = p, ¬q, r, ¬s …W3 = ¬p, ¬q, r, s ………Only one of these worlds can be the actual world, that is a world with all true conjuncts. Possible world conjuncts must be capable of being true individually and together. For example, The prime minister is a prime number isn’t even possibly trueSaying God exists in some possible world means the proposition: God existsis true in some maximal description of reality. Thus God is ‘maximally excellent’ in every possible world: God has ‘maximal greatness.’To have Maximal Excellence is to possess great making properties. Great making properties are things like omniscience, omnipotence, moral perfection, etc. But we can gradually discover what a great making property is, without undermining the objective notion that God would, by definition, possess all such properties. Maximal Greatness is thus possibly exemplified. But then it must exist in a maximally excellent way in every possible world, including the actual world, therefore God exists.a priori Warrant for P1A maximally great being is intuitively coherent and so therefore possibly instantiated. Thus in order for the argument to fail the concept of God must be logically incoherent. But a maximally great being doesn’t seem even remotely incoherent, so we have at least prima facie warrant for thinking it’s possible that a maximally great being exists.a posteriori Warrant for P1Plantinga says that if we “carefully ponder” 1, and objections to it and if we consider its connections with other propositions we accept / reject and we still find it compelling, then we’re within our rational right to accept 1. This recommendation is a far cry from the a priori speculations decried by modal skeptics. For even if we cannot come to a priori warrant, we’re rational in accepting 1 by a posteriori warrant from successful arguments such as the cosmological and moral arguments for the existence of God. Consider the Conceptualist Argument, 1. Abstract objects, such as numbers & propositions, are either independently existing realities or else concepts in some mind 2. Abstract objects are not independently existing realities. 3. If abstract objects are concepts in some mind, then an omniscient, metaphysically necessary being exists. 4. Therefore, an omniscient metaphysically necessary being exists. Premise 1 would simply require a refutation of Nominalism (view of non-existing abstract objects), which has already been accomplished and can be found, http://philmat.oxfordjournals.org... Premise 2 simply requires a Platonism Refutation, which has already been accomplished in the literature by showing not only how abstract objects are causally isolated, but are also irrelevant to what transpires in the world. Premise 3 excludes abstract objects as grounded in a human mind, for there are just too many abstract objects to be grounded in anything less than an infinite mind; and since many of these objects exist necessarily, they can’t be grounded in any contingent mind. Thus this leads us to a conclusion which supports premise 1 of the ontological argument. Surely, though, it just seems obvious that a metaphysically necessary being is the ground for abstract objects which are themselves metaphysically necessary; at least more obvious than any negation offered thus far. Hence we’re within our rational right to affirm the possibility of God, from which it follows God must exist.