In the conversation on divine simplicity over at the Theopolis Institute, Mullins’ most recent response draws attention to the three premises that are “only affirmed by proponents of divine simplicity”:

9. All of God’s actions are identical to each other such that there is only one divine act.
10. God’s act to give grace is identical to God’s one divine act.
11. God’s one divine act is identical to God’s existence.

After which come the following steps:

12. Therefore, God’s one divine act is absolutely necessary.
13. If God’s one divine act is absolutely necessary, then God’s act to give grace is absolutely necessary.
14. Therefore, God’s act to give grace is absolutely necessary.

This implication is problematic for Christians because we hold that God is free to withhold grace if he chooses, which means his act of giving grace cannot be necessary.

But, while proponents of divine simplicity do indeed affirm (9)–(11), we reject (13) and therefore reject the conclusion in (14). In order to see how this works, it would be good to consider a parallel argument involving a more familiar situation. Imagine that whenever Alice is put in some circumstance C she must choose between two options, A and B. Assuming that Alice has libertarian free will, in some possible worlds she will choose A and in other possible worlds she will choose B. Supposing that in the actual world she chooses A, we have the following argument:

1. Alice’s choice of A is identical to her choice between A and B.
2. Alice necessarily chooses between A and B in circumstance C.
3. Therefore Alice necessarily chooses A in circumstance C.

Now, (3) is false on our supposition about Alice’s free will. The problem with this argument is that (1) is ambiguous. If the identity in view is necessary (that is, if “Alice’s choice of A” is a rigid designator for “Alice’s choice between A and B”), then the argument is valid but the premise is obviously false. If, on the other hand, the identity in view is world-relative (that is, if it is just making a claim about the actual world), then the premise is true but the argument is invalid by virtue of committing a modal scope fallacy.

To give a common example of this fallacy, consider the following argument which is a direct parallel of our choice argument:

1. The number of planets in our solar system is identical to eight.
2. Eight is necessarily greater than seven.
3. Therefore the number of planets in our solar system is necessarily greater than seven.

The first premise of this planet argument suffers the same ambiguity and pitfalls as the first premise of the choice argument. The reason for this in the choice argument comes down to the nature of libertarian choice: the same act of choosing can amount in different choices in different worlds.

But there is a subtle and interesting response lurking in the vicinity. In libertarian choices, the response goes, the choice between A and B is a deliberative act which consists in Alice weighing the reasons for preferring A over B up against the reasons for preferring B over A, while the choice of A is the resultant act of Alice pursuing A. Thus, despite initial appearances, the choices are not identical acts, but are two distinct acts, one of which causes the other in a non-deterministic way. In God’s case, however, we have one act rather than two, and so the parallel doesn’t work.

Does such a response rebuff our objection? I don’t think so, for it still grants that there is indeterminism in the deliberative act, which is sufficient for our purposes. With this we can reframe the choice argument as follows:

1. The act that causes Alice to pursue A is identical to her deliberative act.
2. Alice necessarily engages in her deliberative act in circumstance C.
3. Therefore, Alice necessarily engages in the act that causes her to pursue A in circumstance C.

We see here the same problems with the identity in premise (1), despite granting the distinction introduced by the response.

But can we just ignore Alice’s second act of pursuing A? Here we must appreciate an important difference between God’s choices and ours. Alice’s pursuit of A does not belong to her choosing per se, but rather to the execution of the choice she had already made in her deliberative act. Humans need this additional step because our actions find their expression through our bodies — we need to move somewhere, communicate something, start a new thought process, or something else. But God needs no additional act of execution, he acts without need for mediation — he does not need to work through a body and does not depend on other things to bring about his effects. God’s one divine act consists of him choosing which world to actualize based on the the contrastive reasons for preferring each world over the alternatives, including factors such as whether to create anything or not, and whether to give grace or not. This is analogous to Alice’s deliberative act, although without any need for actual deliberation, since God is immediately aware of the all the relevant reasons and does not need to weigh them up successively. And because God is not limited like we are, this one act immediately produces its effects rather than requiring a follow-up act to bring it about.

So, proponents of divine simplicity should reject premise (13) of Mullins’ argument because the identities in premises (9)–(11), while true, are not sufficient to do the work he needs them to do.