Unfortunately, the response was unresponsive to anything I've argued. It is comprised of going on pop-Calvinist auto-pilot and throwing out a few vague terms as if they're really doing serious philosophical or theological work.
The first issue is that it was assumed that the distinction between "moral and natural ability" somehow provided a workhorse of a conceptual tool, the mere mentioning of which, without direct reference to anything I wrote, sufficed to settle the matter. I see neither of them read my essay on free will. I'll plug it again. One problem from the start is that we're talking about determinism, and the above conceptual distinction, while maybe stating a vague truth, does not address the issue raised. For libertarianism is compatible with the distinction between moral and natural in/ability. I went over this in the above mentioned paper.
Phil writes, "There are two sink holes to fall into regarding the idea of a God who is so sovereign that He determines all things ahead of time, denying his sovereignty . . . and denying his goodness." Phil thinks I've done the latter, but cannot demonstrate it from anything I've said. In any case, see that he admits that God "determines all things ahead of time." So, if X determines that S will Φ at t, then S cannot do otherwise than Φ at t, given the determinism (whether it's laws of physics, the fates, laws of logic, or God's decrees). So, per Phil's statement, if God decrees that Phil will eat pizza at noon tomorrow, then given that decree Phil cannot do otherwise than eat the pizza at noon tomorrow.
Now, let's get one thing straight from the start. Phil claimed that a necessary constraint for a sincere offer is: Necessarily, if S sincerely offers Φ to S′, then S can give Φ to S′. Call this Phil's Principle, PP. My counterexample was simple. Suppose Phil offered a slice of pizza to his neighbor, David. David accepts. This looks like a sincere offer. However, suppose God decrees from eternity that Phil will be overtaken by ravenous hunger the moment the pizza arrives (perhaps he was vigorously playing pirate in his backyard tree house). Given Reformed theology and the meaning of "determines," Phil could not have given what was offered to David. There, counterexample, so the constraint has been falsified. Interestingly, Phil thought if he changed subjects about reprobation, positive and negative determining, natural and moral in/ability, etc., that that would somehow save him. No, I'm afraid he's wrong. My counterexample shows that PP is false. Thus, it's not a necessary condition. Phil can qualify, move goal posts, etc., but as stands, I refuted PP.
However, Phil really thinks his points should be taken seriously. And even though they're off topic and unresponsive to my argument, I suppose I can answer him further. Aside from his moral/natural in/ability distinction not doing the compatibilistic work Phil intends for it to do, there's general problems. To say that S has the natural ability to Φ is to say that there's nothing coercing or forcing S to Φ. S does what S does unimpeded by external or constraints. Nothing is forcing or stoping S from Φ-ing. For example, suppose S gets on a bus. To say he has the natural ability to refrain from this, means that there was nothing forcing or coercing S from getting on the bus. His body-parts and the movements thereof worked sufficiently normal to be able to move his body down the street the Chuck E. Cheeze's rather than on the bus. Calvin gives the example of the bones of Jesus. Were they breakable? In one sense, yes; in another, no. In the first sense, they were normal bones, which had the property of breakability if hit with sufficient force, just like all normal bones. In more contemporary terms, Jesus didn't have Wolverine's skeleton. In the latter sense, however, since God had decreed that no bones would break, and since the negation of one of God's decree is impossible to bring about, then the bones couldn't be broken.
Now, those who employ the natural in/ability distinction will use it to argue for compatibilism in classical compatibilist fashion (classical compatibilism is the compatibilism of Hume, Locke, etc.) Since they affirm theological determinism, and they feel the push from questions about how it is just to hold a man responsible if he could not do otherwise, they will claim that man is naturally able to do otherwise, just not morally. The former is what it needed to ground ascriptions of responsibility. So the argument will run like this: S was responsible for Φ-ing because S could have done otherwise than Φ. This 'could have done otherwise' means that S had the natural ability to do otherwise in that nothing coerced or forced S to Φ; and, had S wanted to Ψ instead of Φ, then S would have. This last part is crucial. it invokes the notion of hypothetical ability. That is, we have an ability or power such that were we to want to do otherwise, then we could or would do otherwise, nothing prevented us from doing otherwise in the sense of forcing or coercing.
However, note a couple problems. First, if S did want to do otherwise, and so would do otherwise, this requires another decree. S cannot do otherwise given identical decrees. This brings in possible worlds semantics, but David Ponter taught us that this was strictly forbidden. Second, notice that the move works only if we are able to want to do otherwise. Are we? Well, how does 'ability' get cached out on classical compatibilst terms? Recall that it gets cashed out this way: S is able to do otherwise means that if S were to want to do otherwise, then S could or would. It gets cashed out hypothetically. S is free to Φ if and only if (i) if S chooses Φ then S would Φ and (ii), if S were not to choose to do Φ then S would not do Φ. The bottom line here is that what S chooses to do results from S's will, volition, desires, wants, whatever. So, it's not enough to say that S would have done otherwise had S wanted to, for S also needs to be able to want to. The problem brought out here is that the hypothetical account isn't enough. We need more than just, S could have done otherwise if S had wanted to do otherwise. But this pushes the question back to whether the agent could have wanted to do otherwise. To answer that requires another 'could' statement: S could have wanted or chosen to do otherwise. This requires another hypothetical analysis: S could (or was 'able' to) have wanted or chosen to do otherwise, if S had wanted or chosen to want or choose otherwise. The same question would arise about this analysis, needing another 'could' statement to be analyzed, and so on ad infinitum.
There's other worries too about the sufficiency of the above kind of position. Take cases of mental illness. Clearly a mental patient can do what she wants, or may want to do what she can; say, shoot all the giant elephants walking around New York city (actually, they're people but she hallucinates), but we clearly wouldn't call her free, this is why we send her to a hospital rather than a jail. We need rather more than mere natural ability and doing what we want to do.
In any event, Phil offers a response:
And with that we're ready to address Mr. Manata's question: if God has foreordained that Mr. Bob would spend eternity in Hell, then how can He make a genuine offer of salvation to Bob? The answer is easily found: God happens to know that man left alone will choose hell, but even so He is not condemning man to hell with His decrees. Man is given the empty space to make His own decision, and chooses himself.
Note that this does nothing to undermine my use of an arbitrary example of an offering which refuted Phil's necessary constraint. Second, God doesn't just "happen to know" that man left alone will choose hell, for God has decreed all of man's choices, since he decrees "whatsoever comes to pass." As Berkhof has pointed out,"The execution of the plan may require means or be dependent on certain conditions, but then these means or conditions have also been determined in the decree. God did not simply decree to save sinners without determining the means to effectuate the decree. The means leading to the pre-determined end were also decreed." Third, God condemns man to hell for his sins, which he determined, by the way. If this is rejected, then we must deny that God has decreed whatsoever comes to pass. That God did not directly cause the man to sin is of no consequence, for that simply means that God is the actor. And yes, man makes his own decisions and choices, which of course were decreed before the foundation of the world. Moreover, responsibility and inability to do otherwise is fully compatible with determinism. So, there is a sense in which man makes his own choices, yet he could not have done otherwise. And aside from these objections come objections from the foreknowledge argument. I ask Phil again, what Reformed answer will he give to the foreknowledge argument, which concludes that we cannot do other than we do?
So again, the problem is clear. Phil thinks that there not being any atonement available precludes a sincere offer. I have of course refuted this constraint, and also conjectured that if per impossible a reprobate were to come to Christ, God would send again Jesus to die just for him. This would need to be shown to be impossible. Aside from this, however, is that Phil is faced with a similar problem, and it's the one all non-Calvinists give. Since man cannot accept the gospel, then it looks as if God is insincere to offer it. It's akin to offering a man in a wheelchair a treat if he will come and get it. This is not avoided by saying that you have enough of whatever it is such that you could give it to him if he came. And the appeal to natural ability is not relevant here, that's an accidental detail of the situation. The problem lies in the inability in general. If saying, "Well if the man could walk, then he'd come" doesn't mean anything since he's unable to walk in this world. Similarly the reprobate. Given God's decree that a man will not want to come to Christ, and the positive decree is a necessary condition for coming to Christ, that man cannot come to Christ. He's unable. To say he is able in the sense that if he wanted to come he could invites questions about whether he's able to want. Etc.