I have been preparing for a phil religion class I will be teaching in the Fall and so have been thinking about a lot of these issues. Today I was reading Platinga’s defence of Human free will with God’s foreknowledge of what we will do. He formulates his defense in terms of a scopal difference so, (1) is true but 2 is false (where K(x)=God knows that I will do X in advance and D(x)=I actually do x)
1. [] (K(x) –> D(x))
2. K(x) –> []D(x)
2 is false according to him because there is a possible world (not the actual world) where I do not do X even though God knows that I will do X in the actual world. One thing that worries me is that (1) is equivelent to (1′)
(1′) []K(x) –> []D(x)
and (1′) does seem to entail that I am not free…
He then considers Pike’s modification of this argument which claims that it is an essential trait of God that he is omnicient. Pike’s version of teh arguement is that if God knows at T1 that I will do X at T2 then, if I do not do X at T2 I make the belief that God has a T1 false and this means that God is not omniscient. Plantinga’s response is to point out that to say that I could have done otherwise is to say that there is a world W where I do do otherwise but that this does not mean that God holds a false belief in the actual world.
The problem with this line of argument is that it assumes a view of possible worlds (i.e. Plantinga’s view!) that I find objectionable. To say that I could have done otheriwse is NOT to say that there is a possible world where I do do otherwise and that that world might have been actual! It is to say that I, in this world, might have done otherwise. Adapting Kripke’s humphry objection we can say that it is cold comfort to be told that my being free means that there is someone else who could have done something different than I did. That is nonsense! What it means to be free is that I, myself, could have done otherwise. So if I could have done otherwise in the actual world then God cannot know at T1 what I would do at T2 or if He does then I am not free. So I just don’t see why Plantinga’s response is anything more than question beging…unless I am missing something?
Richard Brown 
Hi Richard. I think you misunderstand Plantinga’s position. You write:
“It is to say that I, in this world, might have done otherwise. Adapting Kripke’s humphry objection we can say that it is cold comfort to be told that my being free means that there is someone else who could have done something different than I did.”
Plantinga has argued vigorously in defense of transworld identity, so I think he would agree that *you*, and not some counterpart-theoretic surrogate, might have done otherwise.
As for doing otherwise in *this very possible world*, I think that is incoherent, since possible worlds are (or ought to be) individuated in terms of what is true in them. So let’s dub *this* possible world, the one that happens to be actual as a matter of contingent fact, Kronos. Suppose you preform some action R in Kronos. Could you have failed to preform R in Kronos? You could only if it is true in some possible world w_1 that you preform R in Kronos, but in some other possible world w_2 it’s true that you don’t preform R in Kronos. So do you preform R in Kronos or not? According to Plantinga, to say (in general) that p is true in some possible world w is just to say that p would have been true if w had been actual. So he’s not offering a reductive account of modality like Lewis. Given that, I’m afraid I just don’t see what the problem with his account is. (You might want to check out Plantinga’s “Essays in the Metaphysics of Modality” and “The Nature of Necessity”, where he deals with these and similar issues at great length.
Thanks Jason, that helps…but I still think something fishy is going on…perhaps it is because I think that possible worlds are stipulated not individuated…but I have to run out the door…I’ll think about this some more and get back to you…thanks again!
You know I was thinking about (1), (1′) and (2) above. It seems to me that we canuse (1) to prove (2)….here’s the proof…it’s a reductio…let K(G,R,a) stand for ‘God knows at T1 that Richard will do action a’ and D(R,a/x) be ‘Richard actually does action a/x at T2’…then let us assume for reductio
1. -(K(G,R,a) –> [] D(R,a)) assumption for reductio
2. –(K(G,R,a) & -[]D(R,a)) from one by def. of material imp.
3. K(G,R,a) & -[]D(R,a) double negation elimination
4. K(G,R,a)
5. -[]D(R,a) from 3, conjunction elimination
6. [](K(G,R,x) –> D(R,x)) assumption
7. []K(G,R,x) –> []D(R,x) distribution
8. -[]D(R,x) –> -[]K(G,R,x) contraposition
9. -[]K(G,R,x) 5,8 modus ponens
10. -K(G,R,a) from 9, instantiation
11. K(G,R,a) & -K(G,R,a) 4,10 conjunction intro.
13. K(G,R,a) –> []D(R,a) 1-11 reductio
I have not used any quantifiers, though I should have, just to make it eaiser. I am pretty sure that the addition of quantifiers does not pose a problem for the proof…Notice that 6. is supposed to true according to Plantinga so I don’t think he can object to me assuming it….Now, since he clearly thinks that 13. is false he must be assuming some kind of modal semantics that invalidates this proof…either that or I messed up the proof somehow…what do you think?
ooppsss premise two is supposed to be ‘ not not’ i.e. double negation, but it looks like a single negation…
What happens to the box between 9 and 10? It looks to me like all you get by instantiation on 9 is ~[]K(G,R,a), which is consistent with K(G,R,a). So this would be one suggested countermodel: K(G,R,a) and D(R,a) are both true at w0. but false at w1 (s.t. w0-R-w1). Then it will be true at w0 that at every accessible world,
K(G,R,a) -> D(R,a),
but it’s false at w0 that
K(G,R,a) -> []D(R,a),
since w0 can see w1 in which D(R,a) is false.
Hi Richard, note that your 5 is -[]D(R,a), whereas modus ponens with 8 requires -[]D(R,x).
re: your original post, (1′) is no problem because the antecedent is unlikely to be true.
But I’m sympathetic to your objection about possible worlds. One way to bring this out is to distinguish between the world itself (as a bare particular), and the various possible world-states it could have exemplified. [More here.] You might then think that whether we are truly free depends on whether we have the power to bring about any number of different world-states. That is, at T1 it should not yet be fixed what will happen at T2 – say whether our world-state is one where you X or not.
Hey Richard,
No, I did not notice that! D’oh!!!!! I thought it was too good to be true 🙂 I guess that’s what happens when you do this stuff late at night…let’s see if early in the morning is any better…
1. [] (K(G,R,a) –> D(R,a)) assumption
2. [] ~(K(G,R,a) & ~D(R,a)) def. imp.
3. [] (~K(G,R,a) v D(R,a)) de Morgan’s laws
4. []~K(G,R,a) v []D(R,a) dist.
5. ~(K(G,R,a) –> []D(R,a)) assumption
6. ~~(K(G,R,a) & ~[]D(R,a) 2, def. imp.
7. (K(G,R,a) & ~[]D(R,a)) def. double neg.
8. K(G,R,a) 7, conj. elim.
9. ~[]D(R,a) 7, conj. elim
10 []~K(G,R,a) 4,9 disj. syll
12 ~K(G,R,a) inst.
13. K(G,R,a) & ~K(G,R,a) conj. intro.
So we either have to rehect 1 or 5 and since everyone accpets 1 as true we should reject 5 and conclude that if God knows that I will do some action ahead of time then it is necessary that I do that action…and so lack free will…shesh…I gotta take a break…
Hi Aidan,
Thanks for the comment!
Yeah you’re right about that…what I was thinking was that 9 was equivelent to ~K(G,R,x) and that would get you ~(G,R,a) but at most it would get me ~K(G,R,b) which is a different matter…what do you think of the second attempt? I guess it is the step from 3 to 4 that must be messed up…
Aha! I knew something was screwy here…
4. should be
4′ ~K(G,R,a) v D(R,a)
I think I may have to give up…
dang, 4′ is supposed to be
4′ ~K(G,R,a) v D(R,a)
hey….the diamonds keep dissappearing…it is supposed to say ‘either it is possible that He doesn’t know or it is possible that I do it’
Richard I read your post…thanks. I completely agree. But that just makes me think that there must be some way to prove K(G,R,a) –> []D(R,a)….maybe I won’t give up… 🙂
[…] Think) I Got It! If you have been following the discussion in Plantinga on Free Will and Omiscience you will have seen that I have been struggling to construct a proof of (1), which says that if God […]
Hey,
Can anyone here without some crazy proof explain to me Plantinga’s belief that God’s omniscience is compatible with human free will? I feel like Plantinga is attempting to say that for a action that is either going to happen or not there are two possible worlds A (where the action occurs) and B (where the action does not occur). At the time the action occurs, T2, you have the chose which world to make actual A or B, but the catch is God knew all along which world was actual. How is this free will if God knew which choice you were going to choose? I know I missing something, but I am not sure what.
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