The topic of God’s knowledge is admittedly a difficult one for human beings to discuss, given that the subject is so far beyond our ken. But, over years of reflection, the church has come up with at least two kinds of divine knowledge which almost all theologians have agreed God possesses:
Natural knowledge: God’s knowledge of what is necessary (such as his being) and what is possible (such as what things he can create).
Free knowledge: God’s knowledge of what he has created or decreed to create.
On the classic definition of the term, knowledge is just “true, justified, belief.” While things like externalist views of knowledge and the Gettier problems have complicated this analysis of knowledge, most philosophers will still want to include the “true” component in their definitions. Of course, many contemporary epistemologies will deny an infallibilist criterion to knowledge, which allows for the possibility that someone can have a warranted belief in something (which we could call knowledge) which actually turned out to be false.
However, on classic definitions of God, no such criterion for something to be knowledge is required to know that God must have infallible knowledge, since infallibility is a property of God himself. He is infallible, so his knowledge must be too. This means, then, that all God’s knowledge must be of true things.
This leads to another age-old philosophical discussion: what is truth? Or in other words: what makes something true? By far the oldest and most popular answer to this is what could be generally called the “correspondence theory” of truth. This was most simply expressed (in my opinion) by Aristotle, who said that truth is “saying of what is, that it is”. Thus, knowledge, at least for God, must be belief of something that is, that it is. For him to know something, that something must exist in reality (in some form).
It is easy to understand, then, what God’s free knowledge corresponds to in reality: it corresponds to everything that exists in reality distinct from Himself. Further, God’s natural knowledge corresponds to knowledge of himself: he knows what he is, which includes knowing his capability, which includes knowing everything that can possibly be created.
But Molinists add another kind of knowledge to God’s mind: middle knowledge. This is knowledge of what any libertarian-ly free creature would do in any given circumstance. Theopedia helpfully summarizes the use that Molinism puts to the doctrine of middle knowledge, in explaining how God’s foreknowledge is grounded in such a way as to preserve libertarian freedom. It explains the logical sequence of God’s knowledge in the following order:
1. God’s knowledge of all possible and necessary truths (natural knowledge — of what could happen).
2. God’s knowledge of all feasible worlds (middle knowledge — of what would happen through free choices under certain circumstances, including counterfactuals).
3. Divine decree to create His selected world.
4. God’s Foreknowledge set through His selected decree (free knowledge — of what will come to pass).
One of the main recurring objections to this form of divine knowledge is known as the grounding objection. I want to briefly trace this objection.
Firstly, middle knowledge, by definition, cannot be God’s free knowledge. God’s free knowledge is of what is (or will be), and not what could be (or could have been). Furthermore, God’s free knowledge exists logically subsequent to God’s decree to create, whereas his middle knowledge is (supposedly) independent of such knowledge.
Secondly, middle knowledge cannot be grounded in God’s being or will. If it were the former, it would be knowledge of facts that necessarily emanate from God’s being. If it were the latter, it would be knowledge of facts that God has causally determined to be true. But, by definition, middle knowledge is knowledge of things that are not necessitated by anything; it is knowledge of what indeterministically free agents will indeterministically choose to do.
The grounding objection is this: the supposed middle knowledge of God is not grounded in anything. There is nothing in reality for it to correspond to. It cannot correspond to his being, nor can it correspond to his will, since in both cases we would have determinism. On the other hand, since it is supposed to be distinct from God’s free knowledge, it cannot correspond to what creatures have chosen to do, or have somehow communicated to God that they could (or wish to) do. Rather, in the Molinist scheme, middle knowledge is supposed to be the knowledge God uses to construct his providential plan, before the world exists. It is the knowledge he uses to decree a particular historical sequence, and thereby ground his foreknowledge of history. (Or, on an atemporal view of God, it is at least knowledge used to construct God’s plan for what will happen in history, and thus cannot possibly be based on what has actually happened in history. This is only reinforced by other aspects of God’s being, such as aseity, which implies God does not have cognitive potential actualized by creatures.) Thus the facts that God knows in middle knowledge are neither facts about the Creator, nor facts about creation. In a Christian worldview, though, those two terms comprehend everything that does or could exist.
But if there is nothing for the content of this middle knowledge (i.e., counterfactuals of creaturely freedom) to correspond to, this content cannot be true. This follows from the definition of truth: saying of what is, that it is. And from this, it follows, middle knowledge cannot be possessed by God: for knowledge (or at least divine knowledge) must, by definition, include belief in something that is true.