What is Platinga's conception of free will?
Recently, I read God, Necessity, and Evil by Alvin Platinga and I really enjoyed it. One thing that I cannot quite wrap my head around is what exactly his conception of free will is, in particular what it is with respect to God.
This is probably not a Platinga specific question, but broadly a question about the compatibility of free will with an Omnicient being.
Let's say we have a world W and a person in this world Hamid. In Platinga's reckoning, if there is an action A such that Hamid is free with respect to this action in W, then God knows whether Hamid will take action A or refrain. Let's say that given the state of W Hamid would refrain. Skipping over A LOT of detail, the upshot is that God cannot create a version of W where Hamid is both free and he chooses to perform A.
Now suppose there is a world S where Hamid is not free with respect to A, and nevertheless he does not perform A. Meaning that S is identical to W, except that in the former Hamid is not free with respect to A.
My question is, what is the difference between W and S from God's perspective. How can God distinguish between W and S? Is "Hamid is free with respect to A" a proposition in the book of W (and its negation in the book of S)? Is "If free with respect to A, refrain from it in W" part of Hamid's essence?
If this latter is true, and if Hamid's essence is instantiated by God, then in what sense is Hamid's choice free? In this telling, it seems more like free choice is a logical constraint God places on himself, and which makes very little difference to Hamid.
Thanks in advance for your responses!