Most people have never thought about the problem of foreknowledge in terms of formal philosophical arguments; nevertheless, many of us have an intuition that perfect foreknowledge cannot be reconciled with free will.
I think that intuition generally follows a thought process something like the following: Whenever I know something about the future, I know it because something about the way the world is now means that the future must necessarily be a certain way. This is the only way I can truly know something about the future; in fact, knowledge of the future is impossible unless the future is determined by the past and present. So if God knows what our future “choices” will be, we really have no “choices” at all, because they have all been determined. I never could have done otherwise, and thus have no free will.
At the end of the day, this line of reasoning could turn out to be correct. But, for my part, I think it fails to distinguish between human epistemology – the processes by which humans obtain knowledge – and divine epistemology – the processes by which God obtains knowledge. It makes inferences about how God thinks about the future from human modes of thinking about the future, without pausing to consider the implications of such an inference.
If God were merely superhuman, I think such an inference would be valid, and He would have a genuine problem on His hands with foreknowledge and free will. But God is not superhuman; He is God. His ways are not just higher than our ways (Isaiah 55:9), but fundamentally different from our ways. And there is no reason, therefore, to assume that God would “anticipate” the future in the same manner that we do, by deduction from the present.
By what other means, then, does He know the future? At the moment, I’m not completely sure; I haven’t given the matter sufficient thought. Perhaps God is “timeless,” as C.S. Lewis suggested in Mere Christianity: “[S]uppose God is outside and above the Time-line. In that case, what we call ‘tomorrow’ is visible to Him in just the same way as what we call today.” Perhaps He has some other means more inscrutable to our imaginations.
Regardless, there is no prima facie reason to limit God’s epistemic tools to our epistemic tools – no reason, in other words, to think of God as the Old Man in the Sky. Thank God for that.