Hi Steve,
I agree with you that there is a contradiction lurking in those assertions. The question is how one might make such a contradiction explicit. CThomas stated that one can only do so by assuming incompatibilism--that free will is not consistent with determinism. We can see that here:
CThomas wrote: I think that you can only get some sort of contradiction if you assume incompatibilism -- that an action cannot be freely chosen (and hence give rise to moral culpability) if that action is ultimately caused by things extrinsic to the deciding agent. Some people just assume this without realizing that it is a very highly contested claim.
CThomas
Now, I personally am going to try to avoid agreeing or disagreeing with this specific claim, because the very terms which CThomas used are susceptible of varying definitions. Therefore, whether one is assuming or not assuming incompatibilism depends upon what one takes to be at the core of the incompatibilist view (e.g. what free will is, and what determinism is). Rather than get caught up in this dispute, I'm going to use CThomas' own view of what counts as a sufficient condition for a free action, which we can find here:
CThomas wrote: As language is ordinarily used in everyday conversation, the key criterion for determining whether a choice was freely made by a person is simply whether the person's actions are determined by the person's decisionmaking processes. Nothing turns on the further question whether those decisionmaking processes themselves turn out ultimately to be physically determined events of a mechanistic brain physiology or, correspondingly, whether they conform to an external decree of God. Rather, a decision is freely chosen, if the person could have chosen otherwise, which means, just so long as the decision was not compelled or coerced by forces outside the person's own decisionmaking processes. It seems to me that what sometimes gets presupposed without argument is the further point -- essential to disproving compatibilism -- that the foregoing is not the ordinary or appropriate means of specifying what it means to make a free decision. It certainly seems to conform to ordinary usage.
CThomas
Thus it is sufficient for an action to be free if the agent had the ability to act otherwise than he did. Without delving into what it means to be able "to act otherwise," we can nonetheless construct an argument that God's decreeing of all of our actions (or even a subset of them) makes us un-free:
1. If I am morally responsible for doing X, then I must be able to refrain from doing X.
2. If God decrees that I do X, then I am not capable of refraining from doing X.
3. Therefore, if I do X, then I am not morally responsible for doing X.
Now, this is an argument that God's decreeing that I do X means that I am not morally responsible for doing X. We are assuming that God's decreeing is an inviolable sort of thing, which may or may not be an accurate representation of Scripture (I happen to think that God does not decree each one of our actions in this sense, even if he can in fact make such declarations about other things). It seems that that only questionable premise for CThomas, then, is premise 2, which says that we cannot act contrary to God's decrees. This is not something, however, which either the Calvinist or the non-Calvinist would be likely to give up. Both would agree that God can decree things which we cannot go against. However, the disagreement lies in the fact that the non-Calvinist does not believe that God has decreed all of our actions, whereas some Calvinists believe that he has.
But we actually have still not given CThomas what he wanted, which was a contradiction between God's "ordaining" or "decreeing" all of our actions and the notion that we are morally responsible for our actions. Well, if premise 3 follows from premises 1 and 2, then this should be sufficient to give him what he wants as it clearly contradicts the notion that we are morally responsible for our actions. However, I can go one step further and make this statement a further premise in the argument:
1. If I am morally responsible for doing X, then I must be able to refrain from doing X. (stipulation granted by CThomas)
2. I am morally responsible for doing X. (stipulation)
3. Therefore, I can refrain from doing X. (follows from 1 and 2)
4. God decrees that I do X. (stipulation)
5. If God decrees that I do X, then I cannot refrain from doing X. (definition of "decree")
6. Therefore, I cannot refrain from doing X. (follows from 5)
7. Therefore, I can refrain from doing X and I cannot refrain from doing X. (follows from 3 and 6)
And the further contradiction about moral responsibility is as such:
8. I am morally responsible for doing X and I am not morally responsible for doing X (follows from 7)
Thus, I am both able and not able to refrain from doing X, which makes me both morally responsible and not morally responsible for doing X. We can see, then, that the notion of moral responsibility as the ability to act otherwise leads to a direct contradiction when paired with a view of God's decreeing as not leaving the option of acting otherwise.
Now it is up to CThomas to show that "the ability to do otherwise" is strictly a part of the incompatibilist view, so that we must be assuming incompatibilism in order to run this argument. Or, alternatively, to show that it is only the incompatibilist who assumes that God's "decreeing" an action means that I am unable to act against God's decrees. If CThomas is unable to do this, then we have shown that we can argue that God's decreeing of all that we do is contradictory to our being morally responsible agents without assuming incompatibilism.
I hope this was clear.