I've had some very good help with this. Blake Ostler wrote a piece titled "Mormonism and Determinism" for the Mormon journal Dialogue. It's a response to L. Rex Sear's piece on determinism. I recommend reading the entire Ostler piece, but for the purposes of this short post, I wanted to extract what he had to say on God's omniscience.
Because I've defined omniscience as "to know everything", I took that to mean knowing everything, including the future. Call this foreknowledge, or when it comes to God, call this "divine foreknowledge". But let's back up here. Why are we defining it this way? Ostler suggests a better definition: "all that can be known". Rather than simply knowing everything, whatever that really means, maybe we should define omniscience as knowing all that can be known. That's completely different. If something simply can't be known, if it's impossible to know something with any or complete certainty, then that wouldn't mean that you can still be omniscient if being omniscient means "knowing all that can be known."
Okay then, back to God. Ostler lists some propositions that one who rejects infallible divine foreknowledge can still affirm:
- God is omniscient in the sense that he knows all that can be known, but it is logically impossible to know future acts that are free.
- God knows all possibilities, including the present probability of any future event.
- God knows now what his purposes are and that he will achieve them.
- God does not know now, in every case, precisely which contingent possibility will be chosen or become actual.
- God knows now how he will respond to whichever contingent possibility occurs to ensure the realization of his purposes.
Thus, God can ensure ultimate victory and the realization of all of his purposes not because of his omniscience, but because of his almighty power. These features of God's knowledge ensure that God knows all possibilities and future events which are now certain given causal implications (propositions 1 and 2). This view also allows for free choices among genuinely open alternatives (propositions 2 and 4). These provisions suggest that God knows all possible avenues of choices (propositions 2 and 5) and, coupled with God's maximal power, entail that God's plans and declarations of future events will be realized (propositions 3 and 5). Thus, a complete picture of God's providence is possible even though God does not have infallible and complete foreknowledge.And there you have it. The entire essay is worth a read. I highly recommend it. Now to answer the question of God's power. Can he make a rock so heavy that even he can't lift it? I'm thinking we'll have to reconsider our definitions once more.