For a good context for this post please see ‘The Theological Advantages of Molinism’ for a list of relevant discussions on middle knowledge and Molinism.
The second moment to God’s knowledge is His knowledge of the contingent states of affairs that would be produced by an antecedent state of affairs were it to be obtained. Counterfactuals are conditional statements in the subjunctive mood. That is to say, God knows what any free creature would do. This is not because the circumstances causally determine the creature’s choice, but simply because this is how the creature would freely choose. God thus knows that were He to actualize certain states of affairs, then certain other contingent states of affairs would obtain. Middle knowledge does not depend on any decision of divine will; God does not determine what counterfactuals of creaturely freedom are true or false. Thus, if it is true that:
If some agent S were placed in circumstances C, then he would freely perform action a,