The more I study middle knowledge, the more I like it. No, I don't expect to see the demise of the Calvinist-Arminian debates in my lifetime. But when a position comes along that both centrist Calvinists and centrist Arminians can endorse, that can be supported by proponents of both libertarian and compatibilist free will, we might just be on to something.
OK, OK, cut the fancy terminology and tell us what you are talking about, you're saying! Right. Here goes. Middle knowledge is a proposed solution to predestination vs. free will, to divine sovereignty and human responsibility, going all the way back to the medieval Jesuit priest Molina (so sometimes it's also called Molinism).
Classic Calvinists, properly concerned to safeguard divine sovereignty, have typically rejected any theological system that bases God's predestining activity on the basis merely of his foreknowledge of how humans will respond to the gospel, because they're convinced that makes human free choice the ultimate determiner. Romans 8:29, of course, does base predestination on God's foreknowledge, but the Calvinist typically argues that the Greek prÅginoskÅ ("foreknow") there begins already to shade over into the idea of election because in the Old Testament the Hebrew yÄdÄ‘ ("know") often appears roughly synonymous with "choose." That would explain why Paul doesn't say just that those whom God foreknew he also predestined, which could be seen as tautologous, but "predestined to be conformed to the image of his Son."
Classic Arminians and Wesleyans, properly concerned to safeguard human freedom and accountability, have typically rejected any theological system that bases God's predestining activity on the basis merely of his gratuitous election, because they're convinced that makes human free choice ultimately a chimera. They often point out that prÅginoskÅ is not the same verb as just ginoskÅ (which the LXX uses to translate yÄdÄ‘ and that in Greek it most commonly means simple knowledge in advance. Thus predestination is based on God's foreknowledge.
Middle knowledge argues for both! If open theism in recent years has diminished divine omniscience more than orthodoxy has classically permitted, middle knowledge magnifies or expands God's omniscience beyond what most people have thought about. But it makes good sense: middle knowledge claims that God's perfect, infinite knowledge must be able to know not only what sentient creatures will freely choose in all situations in their lives but what everyone would do in every possible situation that they could confront. Even more magnificently, divine and unlimited knowledge must be able to discern what all possibly created beings would do in all possible situations (or, as philosophers like to say, all possible worlds).
So far so good, I hope. Now here's the rub. Because there will only ever have been a finite number of humans created before God brings this world as we know it to an end, that means there remain countless uncreated beings that he could have chosen to create but didn't. So God's very choice to create you and me and not various other people he could have is an act of his sovereign election utterly prior to our existence. Calvinists should be happy. But it is based on knowing what we will and would do in all actual and all possible situations. Arminians should be happy. Thus, William Lane Craig in The Only Wise God defends this view from a libertarian Arminian perspective; Alvin Plantinga in a chapel talk at Denver Seminary years ago did the same from a libertarian Calvinist perspective, and Terrance Tiessen in Providence and Prayer does so from a compatibilist Calvinist perspective.
Nor is all this some highbrow theoretical exercise. It has massive, practical pastoral ramifications. You or someone you care about has just experienced an incredible tragedy. How do we deal with it? Is God still sovereign? Absolutely! Did he know in advance this would happen? Yes. Is Romans 8:28 (just one verse before Romans 8:29--you noticed that, right?) still true that "in all things God works for the good for those who love him" (correctly NIV/TNIV, contra KJV's "all things work together for good. . ." [no, they don't!])? Yes, God is in this situation somewhere bringing good out of it. Did God cause the tragedy? No, he is not the author of evil (James 1:13). Why did he allow it? Because it was part of what was required if he was to create a universe with true human freedom and the freedom to allow the consequences of sin, both directly and indirectly (as in "life in a fallen world") without overruling them except on very rare occasions (which is why we call them miracles when he does).
And both Calvinists and Arminians are right in what they affirm about Romans 8:29 and wrong in what they deny. Both/and wins again!