- It is now true that Clarence will have a cheese omelet for breakfast tomorrow. (Premise)
- It is impossible that God should at any time believe what is false, or fail to believe anything that is true. (Premise: divine omniscience)
- God has always believed that Clarence will have a cheese omelet tomorrow. (From 1, 2)
- If God has always believed a certain thing, it is not in anyone’s power to bring it about that God has not always believed that thing. (Premise: the unalterability of the past)
- Therefore, it is not in Clarence’s power to bring it about that God has not always believed that he would have a cheese omelet for breakfast. (From 3, 4)
- It is not possible for it to be true both that God has always believed that Clarence would have a cheese omelet for breakfast, and that he does not in fact have one. (from 2)
- Therefore, it is not in Clarence’s power to refrain from having a cheese omelet for breakfast tomorrow. (From 5, 6) So Clarence’s eating the omelet tomorrow is not an act of free choice. (From the definition of free will.)
One can find it in both Hasker’s God, Time, and Knowledge and his contribution to The Openness of God. Interestingly enough, this is popular with some Calvinists who cite it as a simple logical refutation of the Arminian theory of simple foreknowledge. But I think it’s too simple. It should be noted that my response is largely an adaptation of what I learned in Dr. Craig’s class.
Hasker begins his argument with “a certain Clarence, who is known to be addicted to cheese omelets” and concludes that “it is not in Clarence’s power to refrain from having a cheese omelet for breakfast tomorrow.” One might surmise that Clarence’s lack of freedom follows from his addiction, but that is not what the argument would have us believe. Reading it as a reductio, if it is in Clarence’s power to refrain, then either two things are true:
(1) God’s past belief about Clarence was false.
(2) God’s past belief about Clarence changed to a true belief.
The first disjunct is made impossible by virtue of God’s omniscience, and the second by the unalterability of the past.
What can we say about this argument? Well, we could challenge the assumption in  that the Principle of Alternate Possibilities is necessary for libertarian free will. While this strategy has some merit, I think it is the weakest way out, so I will not comment on it any further. Instead I will challenge the argument by way of furnishing a third option not considered by Hasker above that will undercut the argument more directly.
To begin, it’s not exactly clear how God’s knowledge constrains Clarence’s actions. If it doesn’t entail any causal constraints, then what does the constraining? Fate? But what does that amount to? So there is a primitive concept here doing some heavy lifting. This should cause us some concern, because like Zeno’s paradoxes, something unintelligible is assumed to make the argument go through.
Second, neither God nor his omniscience is required to get the argument going. Suppose Clarence’s wife Clarissa has intimate knowledge of her husband and his purchase of a dozen eggs and a block of cheddar earlier in the day. Before she goes to bed she correctly believes ‘Clarence will have a cheese omelet for breakfast tomorrow.’ Morning comes, and Clarissa’s true belief is tucked away in the past. Therefore, so the argument goes, Clarence isn’t free to refrain from having a cheese omelet for breakfast. If he were, then either (1) the statements ‘Clarence will have a cheese omelet for breakfast tomorrow’ and ‘Clarence will not have a cheese omelet for breakfast tomorrow’ are both true; or (2) The past statement ‘Clarence will have a cheese omelet for breakfast tomorrow’ changed from a true statement to a false statement. The same problems of bringing about a contradiction and a change in the past apply, but surely Clarissa’s correct belief does not compel Clarence to act as he does.
Third, we should not confuse the certainty of an outcome with the necessity of an outcome. Let p stand for ‘Clarence will have a cheese omelet for breakfast tomorrow.” From the premises:
- Necessarily, if anyone knows p, then p.
- God knows p.
It cannot be derived:
- Necessarily, p.
All that follows is:
To get from  to , one must somehow make  necessary. It will not do to say that ‘God knows p’ is necessary, because God could have created a world where p does not obtain. Thus, p is a contingent truth, and it is compatible with God’s omniscience such that if not-p were the case, say because of Clarence’s free choice, then God would know not-p instead. Interestingly enough, this yields a third possibility not considered by Hasker, which is
(3) Clarence can act such that were he to refrain from having a cheese omelet for breakfast tomorrow, then God would have always known ‘Clarence will not have a cheese omelet for breakfast tomorrow’ instead (plausible).
In any event,  will have to derive its necessity from the unalterability of the past (temporal necessity) if Hasker’s argument is to go through. Is (3) compatible with the unalterability of the past? Hasker might not think so, but he gives us no reason to think that the following two statements are incompatible:
- (A) It is not within anyone’s power to act such that something that was known by God was not known by God (unalterability).
- (B) It is within someone’s power to act otherwise such that if someone were to act otherwise, then God would have always known otherwise.
The power in (A) would have to depend on something like the absurd notion of backwards causation where a present action could materially change the past. However, the power in (B) is merely a counterfactual sensitivity, which is fully compatible with God’s omniscience and human freedom. All (B) assumes is that it is not necessary to change the past in order for our choices to determine the past. And Hasker’s argument does not demonstrate how this is impossible.
The upshot is that the content of God’s knowledge is contingent upon Clarence’s choice, Clarence’s choice is not contingent upon the content of God’s knowledge. Therefore, I conclude that Hasker’s argument is incomplete and underdeveloped.