Having identified the core grounding objection as 'how can counterfactual statements about a persons libertarian free will be true, given they do not actually make the choices in the real world?', we are now in a position to address it.
In the first place, I am inclined to follow Job and proclaim if it is not he [God], then who is it? (Job 9:24). In other words God must in some ultimate sense ground middle knowledge; enabling counterfactual statements to be true. The chain has to start somewhere.
God has libertarian free will; He can create multiple worlds but He actually created one. Given His omnipotence; I see no reason why He could not create multiple universes in multiple dimensions. God is distinct from His creation; He is not His creation. Further, God is distinct from possible creations. What we can do flows from what He can enable us to do.
Middle knowledge corresponds to what we would choose, if God created multiple worlds or a different world than the one He did create. We would be God's creation and therefore distinct from God. What we would be able to choose flows from God’s power to enable us to choose. Due to God’s unique knowledge and power, He does not need to actually create the worlds to know what would happen.
Knowledge of counterfactuals is not epistemically available to us, since we can neither experience counterfactuals, nor can we deduct facts about them from principles; yet God knows them without experience or deduction. God has a unique ability to ‘run scenarios’ by placing hypothetical people in hypothetical circumstances to see what they would do; without actually creating them. I don't think the grounding of middle knowledge goes further than that.
Here's a couple of brief thought experiments that I hope will illustrate some aspects of the grounding of middle knowledge.
Imagine God created multiple universes in multiple dimensions giving people libertarian free will in the various universes. Conterfactual statements about you correspond to what you do in the various other circumstances you are in. Hopefully this little example helps people understand that middle knowledge corresponds to what we would do in other worlds and such knowledge depends on God’s power to create and that the object of the knowledge distinct from God.
Imagine you ‘jumped’ from one dimension/universe to another. Would it still be you in the other universe? Are you hesitant about the idea of ‘meeting yourself’? Science fiction writers often come up with radical explanations for what happens if you ‘meet yourself’ – annihilation or insanity or something. Hopefully this little example helps people understand that ‘hypothetical you is still you’; rather than someone else.
Objections to this sort of grounding will be addressed in the next post.