Nomological necessity is very much determinism. That is why Netwonian mechanics are spoken of as "deterministic." I think that the following excerpt from your response demonstrates some confusion over the nature of determinism, which you take to be equivalent to broadly logical necessity:
Now, I am glad to see you employ what appears to be Plantingan possible worlds semantics, because I think it is a helpful heuristic for caching out our modal intuitions. It also provides us some middle ground upon which to clarify our claims.CThomas wrote:This actually is not at all definitional of determinism. Indeed, the paradigm case of determinism is a clockwork Newtonian universe where every physical event is strictly determined by the prior state of the universe coupled with the physical laws. Yet in this paradigm situation, it is not at all the case that any of these events are necessary in the modal-logical sense. These events are physically determined, but nobody would think that they are necessary in the modal sense of occurring in every logically possible world. Necessity in this case is restricted to analytic truths, which are true in every logically possible universe, whether physically possible or not.
On Plantinga's view of possible worlds, an object X exists necessarily just in case X exists in all possible worlds. Stated differently, for any world W, X exists in W. To say that "X exists in W" just means that if W were actual, then X would exist. The relevant notion of "actual" is taken as a primitive in that the "actual world" is the only world that actually exists, and the rest of the worlds are merely possible. Thus we are able to distinguish between what does and what does not exist, and on this basis we are able to ground at least some of our possible worlds talk.
To say that X is impossible is just to say that there is no possible world in which X exists. Alternatively put, for all possible worlds, there is no world W in which X exists. Therefore, there is no possible world such that if it were actual, X would exist. These two notions give us our understanding of broadly logical necessity and broadly logical impossibility.
Now here is the problem with your claim. You said that "determinism" only applies to things which are broadly logically necessary. That is, the only kinds of things which are determined are things which exist in all possible worlds (and have all of their properties in all of those worlds). I am afraid that this is quite a mistaken view of what it means to call something determined. Further, it is not the only grade of necessity which Plantinga himself recognizes. Take Plantinga's view of necessary properties:
NP) For any object O and any property P and any world W, P is a necessary property of O just in case in every world W in which O exists, O has P.
Thus, I can have certain property, P, necessarily, but this does not mean that I exist in all possible worlds. It only means that I cannot exist without having P. Candidates for human beings typically involve "rationality" and "moral awareness." If X is a human, then there is no world W in which X exists and lacks rationality or moral awareness.
Returning to nomological regularities, if such regularities exist in a world W, then everything that happens in W does so in accordance with the natural laws of W in combination with the initial conditions. This leads to the following principle:
NR) Every world W in which the laws of nature and the initial conditions are the same as the actual world W* is a (physical) duplicate of W*.
This would mean, then, that no possible world W'' exists in which 1) the laws of nature are the same as the actual world, and 2) the initial conditions (at the big bang)are the same as the actual world, and yet 3) W'' is not a duplicate of the actual world W*. The consequence, then, is that it is logically impossible for a world to have the same laws as our world, with the same initial conditions, while being different. Now, this does not mean that the laws of nature are broadly logically necessary, nor the initial conditions, nor the events that take place in our universe. There are possible worlds with different initial conditions and the same laws of nature, and different events take place in those worlds. Or worlds with the same initial conditions and different laws of nature, and different events happen in those worlds as well. This only says that once two specific conditions are satisfied concerning 1) the laws of nature and (2) the initial conditions, then 3) it is impossible that the actual world be different. This is really just a deductive argument put in different wording.
Let's now transfer this discussion over to God's decreeing things. Here is a statement of what it means to say that God's decrees transpire infallibly:
ID (Infallible Decree)) For any possible word W, if God decrees X in W, then if W were actualized, X would be actualized. [That is to say, there are no possible worlds in which God decrees X and X fails to occur (be actualized)].
ID is equivalent to GD (God's Decree): If God decrees that I do X, then necessarily I will do X.
You said that GD is mistaken, because it is too strong. However, I think you will see that you must have GD and ID, otherwise you cannot have the view of God's decrees that you want. For if ID is false, then the following is true (as it is simply a denial of ID):
UD (Uncertain Decree): There is a possible world W such that God decrees that I do X in W, and I fail to do X in W.
If there is no possible world W such that God decrees X in W and X fails to occur in W, then it is impossible for God to decree something and for it to not occur. This is simply the appropriate application of Plantingan possible worlds semantics. To say that X is impossible is to say that there is no world in which X exists. We can put this in terms of logically incompatible objects, with the following as an appropriate parsing:
IO (Incompatible Objects): For any two objects X and Y, X and Y are logically incompatible (it is logically impossible for both of them to be actual) if there is no world W in which X and Y exist (more technically: there is no world W such that if W were to be actual then X and Y would be actual).
There is no world in which there exists 1) a decree of God and 2) something which contravenes a decree of God. Therefore, it is logically impossible for something to contravene God's decrees. There simply is no world in which this takes place. And, in order for it to be possible, there must be a world in which it takes place.
Your alternative reformulated premise 5 ("If God decrees X, then X will happen") reads as such:
RP5) There is a possible world W such that God decrees X in W and if W were actual, then X would be actual.
Clearly this states only that God's decrees are logically possible, not that they are infallible.
As for your statement at the end, I think that this discussion shows why it is mistaken. I do not need to show that, "If God decrees an event X, then it follows that for every X (not just some events) there are no possible worlds where God chose to decree the converse of X, i.e., that there are no decrees of God for which He could not have elected to make a different decree." This would mean that I need to show that God's decree are the same in all possible worlds, thereby making them logically necessary. I both disagree with this notion and believe that it is irrelevant to the task at hand. While it certainly would suffice for determinism to say that even God himself is unable to decree otherwise than he does, I disagree with this notion on theological grounds and think that it is sufficient to show that it is logically impossible for something to contravene God's decrees, without the additional requirement that the decrees themselves be logically necessary.