First, on the concept of "determining". I take it to denote an act which, without any chance of failure, sets an occurrence to happen. This is whence "determinism" gets its meaning: a conviction that everything happens without the slightest chance of anything happening otherwise. My "determining" would not allow such statements as, for example, that the driver determines the course of the vehicle. The driver steers, yes, and usually has some kind of a mental representation of the route ahead, but determining would mean that there be absolutely no chance of anything other than the driver affecting the course of the vehicle. Not one unexpected bump, braking or collision, nothing.
Given that definition, it is hardly surprising that I do not think human beings can determine much in this world. Most people admit this straight away: no matter how well we plan our actions, we may always be taken by surprise. But many people, I believe, still would like to think that within ourselves, that is, in our minds, we can consciously determine things. Our freedom to do what we want might have external limitations, but internally we are free to determine ourselves. Now I have argued, quite persuasively, I think, that this is not the case. Let me recapitulate the essential from my previous post:
If my thoughts were in any way decoupled from the current situation, from the moment of spacetime where I experience myself now, why could I not predetermine my thoughts for all the future situations, up to the moment of my last breath? "But of course", you might say, "you cannot predetermine thoughts to be experienced in future situations, because you don't yet know what kind of situations you will end up in: thus, you have no chance of determining just the adequate thoughts for each situation." Well, that is very true indeed, and has been my point all along. The amazing thing is that it applies as much to the nearest future moment as to the farthest!
So, whatever happens in my mind is not something I (consciously) impose on the situation where I find myself. It is, rather, just another aspect of the situation itself. And this is why, in order to determine my thoughts in a given situation, I would have to determine all the other aspects of the situation as well. Now I think that "situation" would have to be the whole of reality. Let O stand for an occurrence I want to determine. If there were something, let it be X, in the reality that was not determined by me, it should remain possible that even the initially wanted O gets no chance of happening. In short, an undetermined X might prevent O from happening. The chance of X preventing O might be negligibly small, but theoretically, that would be enough: as long as X was not in my control, it could affect other things in unpredictable ways, so that I could not really determine them.
To be sure, that argument rests on some presuppositions that could be questioned. Still, this is only an attempt to clarify the concept of "determining" and suggest that determining, in fact, would require determinism. The only plausible determining agent would, on this view, be an all-determiner, one that sets everything to happen, without any chance of failing or getting surprised by anything. By some, this all-determiner might be called God.
There are many notions of divine omnipotence. Some say God cannot do what is logically impossible, while others maintain he can cause anything except for what free creatures do. But most would admit that God's power is of a determinative kind: if he can do something, he can make sure it happens. Would he be God if he could not? I would like to argue that if God can, and does, determine anything to happen, it entails him determining absolutely everything, at least in the context of one reality. This is because, as explained above, if there were in the reality some thing X that was not determined by God, that X could prevent from happening some other things God would want to determine. So if God is to have any real determinative power, he will determine everything, including X – better safe than sorry!
The above said might still be countered by dividing reality into parts determined by God and parts not determined by him. Let the former be X's and the latter Y's. In addition, one will have to hold that there may be no causal interaction between X's and Y's. This is necessary for making sure that X's can really be determined and that their status as such cannot be undone by any influence of the random Y-things. For example, in the context of Alvin Plantinga's philosophical theology, the free choices and actions of human beings would fall into the Y-category, as they are putatively not determined or determinable by God. But at this point, one is clearly about to establish two distinct realities that are somehow interwoven without being interactive. This seems not very good to me: I am afraid that accounting for some occurrences in the world, for example the bulk of human action, would require interaction between X's and Y's to be possible. Then, the X's could not be strictly determined, which would amount to nothing being determined. The majestic, divine acts of creation would thereby be diminished to mere trying.
Let me be clear about this: at the moment, I am deeply skeptical about any attempts of leaving room for determiners other than God in theistic metaphysics. The difficulty of squaring God's sovereignty with free human agency is manifest in the thoughts of classical theists such as Augustine and Thomas Aquinas. The latter, for example, applied Aristotelian metaphysics, one of the axioms of which goes: "Everything that moves is moved by another." In more abstract terms, this applies to all change from potentiality to actuality, so that everything that becomes actual is sort of pushed into actuality by something else. God is the only constantly actual being that pushes created things into actuality, and thus he is the ultimate cause of everything. At one point, Aquinas reasoned about free will and came to think that God does move "voluntary causes" as well as "natural" ones, but that voluntary actions are nevertheless voluntary because God operates such causes according to their nature. (Summa Theologica, Prima Part, Q83) Technically, it is still him who operates the causes, and no-one else. This detail demonstrates quite well the tension emerging when we want to have one being with real determinative power, and other beings still able to decide something by themselves. Augustine, in turn, thought that a human being cannot will anything else than evil, unless God grants her his grace. This reads that whenever somebody genuinely wills something good, that is due to divine initiative. However, Augustine stressed that God's influence is not experienced by the person herself as manipulation, even though it technically could be seen as such.
As regards God, I think it would be best not to say that he "determines himself". Rather, he simply is the way he is. It would be meaningless to say God determines himself, because, by definition, he would then only be making sure he is just the way he is and not otherwise. In classical theism, God is taken to be immutable, eternal and necessary, and given this he would not have to specifically determine himself to be anything. There are other theistic models as well, such as different kinds of process theism, but it is not even required there that God have determinative power. That is why process theism is not relevant now.
So my primary theological suggestion here would be that if God has determinative power, then all occurrences in the world – the universe, reality, or whichever term you prefer – are determined by him. I think this could most easily be accepted by some Calvinists, whose theological tradition has generally been high on God's sovereignty. And given my recent arguments around the concept of free will (see here and here), I do have understanding for theists adopting that kind of a theology. For sure, its austerity does not appeal to everyone, because it implies that God has determined most appalling things to happen. The alternatives seem to be either to cling on to an unrealistic notion of human free will, or to turn to some kind of process theism.