An article by Stephen T. Davis is useful here. We can pick it up at the point where it cites an argument from Nelson Pike. The article addresses the reconciliation, possible or not, of divine omniscience with human freedom. It isn't my practice to quote longish extracts from articles but the problem we're dealing with is perplexing and its resolution complex. Davis is no more complex than he needs to be, and could not present Plantinga's argument (in my view) with less complexity than he does.
(9) God existed at T1, and God believed at T1 that Jones would do x at
T2, and it was within Jones' power at T2 to refrain from doing x.
(10) It was within Jones' power at T2 to do something that would have
brought it about that God held a false belief at T1.
(11) It was within Jones' power at T2 to do something that would have
brought it about that God did not hold the belief he held at T1.
(12) It was within Jones' power at T2 to do something that would have
brought it about that any person who believed at T1 that Jones
would do x at T2 (one of whom was, by hypothesis, God) held a
false belief and thus was not God - that is, that God (who by
hypothesis existed at T1) did not exist at T1.
What Pike claims is that (9) implies either (10), (11), or (12), all of which
are contradictory or otherwise unacceptable, and that (9) must therefore be
rejected. ...
But I believe Alvin Plantinga has successfully rebutted Pike's claim.
Using a possible worlds ontology, he denies that (9) entails either (10), (11),
or (12). In the next four paragraphs, let me briefly summarise Plantinga's
argument. First, does (9) entail (10)? It does not seem that it does: had
Jones' refrained from doing x at T2 it would follow that a proposition which
God did in fact believe would have been false, but this is surely unproblematical.
What does not follow is (as (10) implies) that God (who is by hypothesis
omniscient) would have believed that Jones would do x at T2 under these
conditions. So (10) does not appear to follow from (9). What does appear
to follow is:
(10/1) It was within Jones' power at T2 to do something such that if he
had done it, then a belief that God did hold at T1 would have been false.
But how does (10/1) create a problem? It certainly does not entail that Jones
can make God hold a false belief. What (9) says is that God believes that
Jones will do x at T2 and that Jones has the power not to do x at T2. And
of course it follows that if God knows at T1 that Jones will do x at T2 then
Jones will do x at T2 (as I admitted earlier). But if it is still logically possible
at T2 for Jones to refrain from doing x - as (9) suggests that it is - we can
capture this possibility by bringing in the modal notion of possible worlds.
Imagine a possible world W, different from the actual world, where Jones
refrains from doing x at T2. Let us call the actual world 'Alpha'. Now in W, a belief that God holds in Alpha is false: so if W had been actual instead
of Alpha a belief God holds in Alpha is false (and either (10), (11), or (12)
would follow). But it does not follow that in W God holds the false belief
that Jones will do x at T2 - unless it is true that an omniscient being must
hold the same beliefs in all possible worlds. But this is obviously not true:
since God is omniscient we can be quite sure that had W and not Alpha
been actual he would have held the correct belief that Jones will refrain
from doing x at T2. Thus it does not appear that (9) entails (10), i.e. that
(9) entails that Jones has the power to make God hold a false belief.
What about (11) - does it follow from (9)? The problem is that (11) is
ambiguous. It is unclear which of the following properly explicates (11):
(11/1) It was within Jones' power at T2 to do something such that if he
had done it, then at T1 God would have held a certain belief and
also not held that belief.
(11/2) It was within Jones' power at T2 to do something such that if he
had done it, then God would not have held a belief that in fact he
did hold.
(11/1) entails that Jones can bring about a contradictory state of affairs, but
it does not appear that (9) entails (11/1). (11/2) does appear to follow from (9),
but is perfectly innocuous: it does not follow from (11/2) that God did hold
a belief that he didn't hold.
And finally, what about (12) - is it entailed by (9) ? Again, it seems not.
What (9) actually entails is:
(12/1) It was within Jones' power to do something such that if he had done
it, then anyone who believed at T1 that Jones would do x at T2
would not have been God.
That is, if Jones had not done x at T2, then if God had believed at T1 that
Jones would do x at T2, then God would have held a false belief and would
not have been God. But in a world W where Jones does not do x at T2,
God does not have to hold the same beliefs that he does in Alpha, and in
this case, he certainly will not.
Perhaps the basic intuition behind this critique of Pike can be expressed
as follows. It is obvious that the following propositions are quite different:
(13) Jones will not mow his lawn tomorrow,
and
(14) Jones cannot mow his lawn tomorrow.
I believe that (13), but not (14), is entailed by 'God knew yesterday that
Jones will not mow his lawn tomorrow'. Nor is (14) entailed by (13). There
simply is no rule of logic that allows these entailments.
(Stephen T. Davis, 'Divine Omniscience and Human Freedom', Religious Studies, Vol. 15, No. 3 (Sep., 1979), pp. 303-316 : 306-7; Nelson Pike, 'Divine Omniscience and Voluntary Action', Philosophy of Religion, edited by
Steven Cahn (New York: Harper and Row, 1970), pp. 68-88.)
NOTE
Philosophy is argument without end. Pike has come back at Plantinga. I am persuaded by Plantinga's argument as presented by Davis and can only indicate further references.
Stephen T. Davis, 'Divine Omniscience and Human Freedom', Religious Studies, Vol. 15, No. 3 (Sep., 1979), pp. 303-316.
Alan Plantinga, God, Freedom, and Evil (New York: Harper and Row, 1974).
Nelson Pike, 'Divine Omniscience and Voluntary Action', Philosophy of Religion, edited by Steven Cahn (New York: Harper and Row, 1970), pp. 68-88.
Nelson Pike, 'Divine Foreknowledge, Human Freedom, and Possible Worlds', The Philosophical Review, LXXXVI, 2, April 1977.
