Actuality and Two Varieties of Possibility
In my previous post I contemplated the idea that actuality is the ontological delimiter of possibility (ODOP). That's a mouthful, but what it means basically is that the reason why one thing is possible rather than another is because something that already exists precludes some things from happening and not others. Here's a simple example: given the actual laws of nature, it is possible that a rock that is dropped will fall but (virtually) impossible that it will remain suspended in mid-air.
Matters are complicated, however, by the fact that there are different types of possibility. The example I just gave has to do with physical possibility. What is physically possible at a given time is delimited by the laws of nature and the physical state of the world at that time.
Another important type of possibility is logical possibility. Generally, something is logically possible if and only if there is a maximal, internally consistent state of affairs (a possible world) in which it exists. For example, is seems that there is a possible world that is just like our world except for the fact that the way colors appear is inverted--what appears red to us in this world appears blue to people in the other world, and vice-versa. Logical possibility is delimited by the laws of logic--most importantly, the law of non-contradiction--because that is what determines whether a maximal state of affairs is internally consistent or not.
There may be other types of possibility as well, but we can set them aside for now. It is important to note, however, that physical possibility is also constrained by logical possibility because physical possibilities are realized within the scope of a given possible world. It's natural, then, to focus first on logical possibility.
The issue now is this: If actuality is the ODOP, including logical possibility, then there must be some sort of reality that transcends all possible worlds. In other words, if W and V are different possible worlds then the actuality that delimits them both cannot be something that is merely actual in W or actual in V. Instead, it must be actual in both of them. And if there are other possible worlds, then it must be actual in them as well. In short, it must have universal transworld actuality. That, by the way, is what it means to be a logically necessary being.
So it seems that the thesis that actuality is the ODOP not only rules out the possibility of a null world (as I argued in the last post) but also requires sort of logically necessary being (or beings?). Moreover, since it is the laws of logic that delimit logical possibility, the laws of logic must either (a) be identical with this necessary being, (b) be part of this necessary being, or (c) be a production of this necessary being.
The examination of these options will have to wait for another post. One would I think be right to suspect at this point that the view that actuality is the ODOP looks rather favorable to theism. Conversely, Lewis's deflationary view of actuality is more amenable to atheism--as he points out in a follow-up to his "Actuality and Anselm" essay, his view of actuality gives him a fairly straightforward way of deflecting teleological (design) arguments for God's existence.
If this is right, then debates on the nature of existence and actuality are not neutral vis-a-vis theism and atheism. That recognition should, I think, give this issue greater importance than it generally receives in philosophical discussion.