True, but in order for foreknowledge to be possible, the future must be determined.
No it doesn't have to be. This is one of those old canards that is having a surprising resurgence of popularity nowadays. But it's really not all that compelling as it confuses the direction of dependency of truth and knowledge.
For a moment, leave God out of the picture and consider the truth value of the following sentence:
(A)
Barack Obama will receive a second term as President.
Question: Is it possible for this sentence to be true or false? I think it is possible. I don't know its truth value, and at least for me, I won't know its truth value until the fateful day when Americans go to the polls again. But there's a truth of the matter which way Americans will vote. And this truth of the matter doesn't change the fact that the Americans will
freely vote this way or that. The way Americans will vote determines whether Obama receives a second term, which in turn determines whether (A) is true. In other words, the free choices of Americans determines the truth of (A); it is not the truth of (A) that determines how Americans will vote.
What changes if we suppose there exists an omniscient deity? Presumably, the deity will know how Americans will vote. But knowledge doesn't CAUSE anything. Knowledge is a RESULT of truth, not a CAUSE of it. Thus there is a way Americans will vote. They will do this freely. The fact that there is a deity that knows which way the vote will turn out does not affect the freedom of the voters.
You might object, if God knows how Americans will vote, there is no way for those Americans to change the way they will vote. I say, that's true, but that's true with or without God. There's a truth value to future propositions. But what MAKES them true is what actually happens. In other words, God's knowledge of (A) is DEPENDENT upon how humans act. God's knowledge doesn't CAUSE human actions, rather human actions cause God's knowledge (of human actions).
In other words, your comment is getting the dependencies exactly backwards. Your comment seems to suggest that knowledge of (A) causes (A) to happen and therefore to be true. But the reverse is actually true. The truth of (A) causes God (or a psychic, say) to know (A).