Here is what I posted in another thread, a thread on theodicy, with two separate posts combined and slightly condensed:
The argument to natural evils against the so-called omni-god — all knowing, all powerful, and all good — is pretty conclusive imo. Still the theodicy practitioner will move the goal posts, offer ad hoc rationalizations, and if necessary fall back on the “mysterious ways” copout.
I feel, though, that the common argument that God’s omniscience precludes human free will should be addressed as a matter of logic. The argument is not just poor, it is logically invalid and ought to be discarded.
It goes:
Today I had eggs for breakfast.
But if God is omniscient, he knew even before I was born — for all eternity, in fact — that I would have eggs for breakfast today.
If God knew even before I was born that I would have eggs for breakfast today, then I could not have had pancakes or anything else for breakfast today. My choice was foreordained by God’s foreknowledge.
Hence, I have no free will.
The argument commits the modal scope fallacy. The fallacy consists in confusing logical contingency with logical necessity.
The fallacious argument goes:
If God knows today that I will have eggs for breakfast tomorrow, then I must (necessarily) have eggs for breakfast tomorrow.
The modal scope fallacy occurs when one applies the logical concept of necessity to the consequent of the antecedent alone, rather than to the conjoint relationship between antecedent and consequent.
The corrected argument is:
Necessarily (if God knows today that tomorrow I will have eggs for breakfast, then I will [not must!] have eggs for breakfast tomorrow.)
The necessity lies only in the relationship between God’s foreknowledge and my free act.
To be sure, If God knows today that tomorrow I will have eggs for breakfast, I WILL have eggs — but it does not logically follow that I MUST have eggs. All that logically follows from God’s omniscience is that what God foreknows, and what I freely do, must MATCH (as a matter of logical necessity).
If I freely choose today to have eggs for breakfast, it means I have provided the truth grounds for God’s foreknowledge of what I do. It does not mean that I could not have had pancakes. For if I had had pancakes, an omniscient agent would have known THAT fact instead — and we would get:
Necessarily (if God knows today that tomorrow I will have pancakes for breakfast, then I will [not must!] have pancakes for breakfast tomorrow.)
I am free to have eggs or pancakes. If I have eggs, God will foreknow that I have eggs. If have pancakes, God will foreknow that I have pancakes. I can have eggs or pancakes, or anything else that I wish. I just can’t escape God’s infallible foreknowledge of what I freely do. To employ modal logic’s logically possible worlds heuristic:
There is a possible world at which I have eggs for breakfast and God foreknows that I have eggs.
There is a possible world at which I have pancakes for breakfast and God foreknows that I have pancakes.
There is no possible world at which I have eggs for breakfast and God foreknows that I have pancakes.
There is no possible world at which I have pancakes for breakfast and God foreknows that I have eggs.
Here is the formal elaboration of the fallacious argument that God knowing in advance what I will do forces me to do that thing:
gKD
~◊(gKD & ~D)
gKD ⊃ ☐D
————————
∴ ☐D
In the above argument, Premise 3 is false. It commits the modal scope fallacy.
The corrected argument goes:
gKD
~◊(gKD & ~D)
gKD ⊃D
————————
∴ D
Reconstructed in natural language:
Fallacious argument:
- God knows what I will do.
- It is not possible that God knows what I will do, and I fail to do that thing.
3.If God knows what I will do, I must necessarily do that thing.
Conclusion: I must do what God knows I will do.
Corrected argument:
- God knows what I will do.
- It is not possible that God knows what I will do, and I fail to do that thing.
3.If God knows what I will do, I will do that thing.
Conclusion: I will do what God knows I will do.
The corrected modal argument eliminates any mention of necessity in my action, which means my action is, was, and always will be, contingent — i.e., could have been otherwise. Therefore I could have done other than what I did. I just can never do other than what God foreknows, but that fact does not impugn my free will in the slightest.
Now — I am adding this here — if my argument goes astray somewhere, and that is possible, it must be challenged and not dismissed. So far as I can tell the corrected modal argument is both valid and sound — the conclusion follows from the premises, and all the premises are true. If so, this makes the argument a deductive proof that God’s foreknowledge does not obviate human free will. A proper challenge to the argument would be to show that the argument is either invalid or unsound, and not to fulminate about electrical engineers and lightbulbs and what “gall” I supposedly have.
I should add that the Christian philosopher William Lane Craig has used this exact line of modal logical reasoning to brilliantly resolve Newcomb’s Paradox: Divine Foreknowledge and Newcomb’s Paradox