A theology of the possible, part 5
The second metaphysical error committed by the hypothesis of God creating the world from a pre-given, universal domain of exemplars, according to Ross, is what some have referred to as “possibilism,” the view that possibility or possible existence is metaphysically prior to and hence determinative of actuality or actual existence, making real existence a mere accident or property of some prior possibility. As Ross characterizes this view of contemporary “modal actualists” (whom he elsewhere also refers to as “Modal Neoplatonists”)—so called because they “postulate universal domains of essences, propositions, states of affairs, and even divine ideas… insist[ing] on the exhaustive panorama of possibles”—they
write as if a property, ACTUALITY, were added to or conferred pon a possible world. But actuality would then accrue to a world accidentally, as something inhering in a subject already in being. Possible worlds cannot be subjects of inherence; for instance, they cannot BECOME actual… Further, the being of things cannot be INHERENT, either accidental to them or to the world ‘they inhabit,’ for similar reasons. If ‘actuality’ is not a predicable accident, a constitutive relation, or a real mode of being, then what is it? Calling it a ‘property’ is just an eyepatch for missing insight. One thing is certain: actual being is not a property and is not even predicable of anything. Those who think ‘Socrates exists’ is like ‘Socrates is tall’ simply do not understand…. (318)
On the possibilist assumption, accordingly, God’s act of creation would reduce to his “adding actuality” to an (in a sense) already “existing” “possible world.” On this view, although God may not create the world from any pre-existing physical matter or potentiality, it is not clear that it doesn’t involve him in creating the world from a pre-exiting intelligible matter or potentiality.
 Christopher Menzel defines “classical possibilism” as being “rooted in the idea that there is a significant ontological distinction to be drawn between being, on the one hand, and existence, or actuality, on the other. Being is the broader of the two notions, encompassing absolutely everything there is in any sense. For the classical possibilist, every existing thing is, but not everything there is exists.” Menzel, “Classical Possibilism and Lewisian Possibilism,” Stanford Encyclopedia of Philosophy, http://plato.stanford.edu/entries/actualism/possibilism.html (accessed 5/24/2012).
 Immanuel Kant famously made the same critique of the so-called “ontological” argument for God’s existence of Anselm and Descartes, namely that it fallaciously treated existence as a perfect-being-making property, without which God would fail, ex hypothesi, to be “that which nothing greater can be thought.” Whether Kant’s critique represents a fair portrayal of Anselm’s argument in the Proslogion, however, is another matter. For a more sophisticated interpretation that may avoid Kant’s objections, see Thomas Williams, Anselm.