I’ve long thought that open theology, the notion that God does not and cannot know future contingent events, is simply consistent Arminian theology. Richard Muller’s description of Arminius’s view of “middle knowledge” (in God, Creation, and Providence in the Thought of Jacob Arminius ) shows that, while Arminius himself did not deny God’s omniscience, he certainly left an unresolved question:

Arminius does not develop his definition of scientia media at any great length, but his very definition of the concept raises a serious question about the extent of divine knowledge and its possible limitation. The definition inserts an element of conditionality into the scientia Dei : “if this happens, that will take place.” Arminius seems to be saying that, according to the scientia media , God has a conditional knowledge of future contingents. God does not, in other words, know a future contingent absolutely as something that will happen. Rather, God knows the future contingent relatively or hypothetically as a potential result of a prior creaturely act. The scientia media , in other words, seems to introduce into the divine mind an element of potency or knowledge of possibility that is actualized by something external to God. At least this is the implication of the conditional element in the definition — and, indeed, of the creation of a category of knowing in between the pure, precreative knowledge of possibles and the absolutely certain postcreative knowledge of positively willed actuality. Is the scientia media merely a knowledge of the results of divine permissive willing (in which case it would be a certain and definite knowledge) — or is it also a knowledge of events that take place outside of the divine willing, whether positive or permissive (in which case it would be an uncertain and indeterminate knowledge) (p. 156)?