Plantinga Calls This A Good Argument for God’s Existence?

The title of my post might come across as snarky, so I want to begin my making it clear that is not my intent. In fact, I want to go on record as saying I have great respect for Plantinga’s skill as a philosopher. Among other things, I think he succeeded in his attempt to refute Mackie’s version of the argument from evil.
Perhaps because I have to come hold Plantinga’s work to such a high standard, I continue to be surprised whenever I read Plantinga’s version of the so-called argument from beauty. In his famous lecture, “Two Dozen or So Theistic Arguments,” Alvin Plantinga sketches what he calls the “Mozart Argument.”

On a naturalistic anthropology, our alleged grasp and appreciation of (alleged) beauty is to be explained in terms of evolution: somehow arose in the course of evolution, and something about its early manifestations had survival value. But miserable and disgusting cacophony (heavy metal rock?) could as well have been what we took to be beautiful. On the theistic view, God recognizes beauty; indeed, it is deeply involved in his very nature. To grasp the beauty of a Mozart’s D Minor piano concerto is to grasp something that is objectively there; it is to appreciate what is objectively worthy of appreciation.

Plantinga doesn’t say how he rates the strength of the individual arguments; it’s possible that he views this argument as providing just a teeny-tiny bit of evidence that is just barely more probable on theism than on naturalism. Of course, it’s also possible that he views this argument as a “killer refutation” of a naturalism. Or, perhaps more likely, maybe he views it somewhere in between.
Let’s evaluate this argument the same way Plantinga evaluates arguments from evil against theism. How do we do that? By trying to clarify the claim the argument makes about the relationship between the evidence to be explained (in this case, objective beauty) and the rival explanatory hypotheses (e.g., theism and naturalism). Nothing in the passage above suggests that Plantinga claims that objective beauty is logically inconsistent with naturalism. Rather, Plantinga seems to be suggesting that objective beauty is less probable on naturalism than on theism.
I’m going to attempt to “steel man” Plantinga’s argument. The most charitable interpretation of Plantinga is that he’s offering the following argument:
(1) Objective beauty exists.
(2) Naturalism is not intrinsically much more probable than theism. [See Plantinga’s argument L]
(3) The existence of objective beauty is more probable on theism than on naturalism, i.e., Pr(beauty|theism) > Pr(beauty|naturalism).
(4) Therefore, everything else held equal, naturalism is probably false, i.e., Pr(naturalism) < 1/2.
I find this argument unconvincing; indeed, I find it so unconvincing I confess I find it hard to understand why Plantinga would endorse it.
First, I think the truth of (1) is far from certain. It’s far from obvious to me that such a thing as objective beauty exists; I don’t even have the intuition that it exists. And Plantinga offers no reason to think that it does. If it doesn’t exist, then there is nothing to explain and this argument cannot even get off the ground.
Second, I think (2) is false. Purdue University philosopher Paul Draper has convinced me that intrinsic probability is determined by modesty, coherence, and nothing else. Again, the only thing I could find in Plantinga’s lecture is a reference to Swinburne’s work on intrinsic probability. Swinburne argues that simplicity determines intrinsic probability. To be sure, there is a correlation between modesty, coherence, and simplicity. But correlation is as far as it goes. And if Draper is correct that intrinsic probability is determined by modesty and coherence, then naturalism is intrinsically much more probable than theism for the simple fact that naturalism (a/k/a “source physicalism”) is much more modest than theism, just as supernaturalism (a/k/a “source idealism”) is much more modest than theism.
Third, let’s assume, but only for the sake of argument, that (1) is true. There really is such a thing as “objective beauty.” What might be the metaphysical or ontological grounding for it? One option is Platonism, i.e., abstract objects. In other words, facts about objective beauty would be nothing more or less than necessary truths about beauty. And since Draperian naturalism (or “source physicalism”) says nothing about whether abstract objects exist, this metaphysical grounding is available not just to theists, but also to naturalists. And Plantinga offers no reason to reject this naturalistic explanation.
Instead, Plantinga considers an evolutionary explanation. Perhaps, he suggests,

our alleged grasp and appreciation of (alleged) beauty is to be explained in terms of evolution: [it] somehow arose in the course of evolution.

But this isn’t an apples-to-apples comparison. Plantinga isn’t comparing a naturalistic explanation of objective beauty to a theistic explanation of objective beauty. On the naturalistic side of the equation, he’s not considering the explanatory power of naturalism to account for objective beauty; rather, he’s considering the explanatory power of naturalism conjoined with an auxiliary hypothesis (about evolution) to account for our grasp and appreciation of alleged beauty. Similarly, on the theistic side of the equation, he’s not considering the explanatory power of theism to account for objective beauty; rather, he’s considering the explanatory power of theism conjoined with an auxiliary hypothesis (about God’s nature) to account for … what, precisely? Our grasp and appreciation of real, not just merely alleged, beauty? God’s causation of objectively beautiful features of the natural world? Something else? Plantinga never says.
The problem isn’t that he invokes auxiliary hypotheses; the problem is that doing so raises a whole bunch of questions which Plantinga doesn’t even ask, much less answer. For example, what’s the antecedent probability of his proffered evolutionary explanation, conditional upon the truth of naturalism? Likewise, what’s the antecedent probability of his auxiliary hypothesis to theism, that facts about objective beauty are somehow related to God’s nature, conditional upon the truth of theism? (And how does that compare to an alternative auxiliary hypothesis about theism, namely, that facts about objectively beauty are grounded in an autonomous realm of abstract objects?) Since Plantinga doesn’t answer these questions, his defense of his Mozart argument is far from complete.
Fourth, let’s assume, but only for the sake of argument, that premise (3) is true. The fact, if it is (were?) a fact, that objective beauty exists hardly exhausts what we (would?) know about “beauty.” As Draper points out, while the universe is saturated with visual beauty, it is not saturated with auditory, tactile, or other sensory beauty. Given that beauty “exists” at all, facts about the kinds and distribution of beauty favor naturalism over theism. So, once the evidence about beauty is fully stated, it’s far from obvious that it favors theism over naturalism.
In fairness to Plantinga, I want to remind readers that Plantinga was merely sketching his Mozart argument in the context of a speech about two dozen or so arguments; he wasn’t trying to give a sustained or even a precise defense of the argument. Nevertheless, I think the above objections pose significant obstacles to such an argument. Even when the argument is steel manned, as I have tried to do here, I cannot see how the argument can overcome these objections.