Steelmanning the Abductive Moral Argument of David Baggett and Jerry Walls

Chad of the blog "Truthbomb Apologetics" recently tweeted about the abductive, cumulative moral argument for God's existence set forth by Christian philosophers David Baggett and Jerry Walls in their book God and Cosmos.

Baggett/Walls: A Four-Fold Abductive Cumulative Argument

1. Moral facts, moral knowledge, moral transformation, and moral rationality require robust explanation.

2. The best explanation of these phenomena is God.

3. Therefore, God (probably) exists. @moralapologetic

— Chad (@TBapologetics) January 21, 2022

As someone with great interest in metaethics and moral arguments for theism, this book had been on my "to buy" list for sometime. I decided to pick up a copy on Kindle. 

With the disclaimer that I haven't finished reading the book yet, the first thing I did after downloading the Kindle version of the book was to scan the book for a schema or other formal representation of the logical structure of their argument in premise and conclusion form. I didn't find one. So I decided to try to "reverse engineer" the schema for their argument as I read through the book.

Inference to the Best Explanation (IBE)

In their Introduction to Part I of the book, Baggett and Walls write:

When we speak of classical theism explaining morality, we are speaking of an "inference to the best explanation" ("IBE," for short) case for theistic ethics. (14)

They then mention three important components of an IBE: 

(1) the set of salient facts requiring explanation, (2) the list of explanation candidates, and (3) the criteria by which we reduce the field of candidates down to the one that is best. (14)

They then provide a convenient overview of the content to come throughout the book, grouped according to these three components. Regarding (1), the facts to be explained, Baggett and Walls write:

An abductive moral argument for God's existence begins with important moral realities. These are an important starting point, and such realities will include ontological matters (moral facts), epistemic matters (moral knowledge), performative matters (moral transformation), and facts about morality and rationality (including the convergence of happiness and moral virtue). (14)

While most of these are fairly self-explanatory, it is helpful to quote Baggett's and Wall's explanation of what they mean by "moral facts."

The sort of moral facts requiring explanation are objective, prescriptively binding moral duties, objective moral values, requisite moral freedom, ascriptions of moral responsibility, and other relevantly similar data of that ilk. (14) 

Let's turn to (2), the list of explanation candidates. As I read Baggett and Walls, their list of explanation candidates includes the following: classical theism, deontological theories, consequentialist ethics, evolutionary ethics, social contract theory, and secular virtue accounts. (18)

Finally, as for (3), they provide the following list of abductive criteria: (a) explanatory power; (b) explanatory scope; (c) plausibility, (d) degree of "ad hoc-ness"; and (e) conformity with other beliefs. 

The Argument Formulated as an IBE

As mentioned above, it is unfortunate that Baggett and Walls fail to state their abductive moral argument for theism in standard logical form. Nonetheless, their discussion (as summarized above) provides enough detail to arrive at a preliminary interpretation. Let B represent the conjunction of our relevant background information; E represent the conjunction of the facts to be explained; T represent classical theism; and A1, ..., An represent the alternative, nontheistic explanations listed above. I propose their argument has the following schema.

1. Hypothesis T of the set {T, A1, ..., An} is the best explanation of the evidence E in being superior to its rivals {A1, ..., An} in satisfying the five criteria for explanation candidates.
2. Therefore, other evidence held equal, T is more probable than naturalism.

The conclusion, stated in (2), seems to be consistent with the first (full) paragraph on page 20, which begins as follows:

This should serve as a needed reminder of a few important points to bear in mind as we proceed. If we were to conclude that classical theism provides, on examination, the best explanation of morality, and even assuming there is widespread agreement on the salient facts in need of explanation and theism's victory, what we can infer is limited in certain respects. First, perhaps morality increases the likelihood of theism but only by a marginal amount. Second, it should be said in such a case that the probability of theism has increased (by much or a little) relative to morality; in theory the probability of atheism could increase or decrease relative to other phenomena.... (20)

In order to evaluate the above schema, we may ask three questions. (1) Does the conclusion follow from the premises? (2) Are the proposed criteria for explanation candidates meaningful, unambiguous, and justified? (3) Does T, in fact, fulfill the five criteria for explanation candidates? In this blog post, I will only consider the first question.

Baggett and Walls explicitly claim that, if successful, their argument raises the probability of theism; they do not claim that, by itself, their argument shows that theism is more probable than not. (In the terminology of Richard Swinburne, the argument of Baggett and Walls is C-inductive, not P-inductive.) Because they use the language of probability, however, this immediately raises the objection: Baggett and Walls do not offer any reason to think that (2) follows from (1). Nor can they. Why? Because the above schema lacks a premise which says that the set {T, A1, ..., An} is jointly exhaustive. In my (admittedly incomplete) reading of their book so far, I have not found such a premise. Nor does this seem to be a mere speculative worry; Christian Miller, in his review of God and Cosmos, raises a related worry. He suggests that Baggett and Walls engage an incomplete set of anti-reductionist ("non-naturalistic") alternative explanations for moral facts and, more broadly, "don't engage in much detail with the leading work in meta-ethics today." So, if Miller and I are correct that Baggett and Walls do not consider a jointly exhaustive set of explanation candidates, this would be a major flaw in their argument. Their argument would violate the laws of probability. 

In fairness to Baggett and Walls (and as Miller notes in his review), the "the field of contemporary meta-ethics is a vast and difficult terrain." And so Baggett and Walls might object that assessing a jointly exhaustive set of of secular alternative explanations is a monumental task because there might be too many. Miller, in his review, suggests that Baggett and Walls raise precisely this point later in the book. Nevertheless, different alternative explanations can be collected together in groups and evaluated as a group. So, for example, instead of discussing anti-reductionist (a/k/a "non-naturalist") theory AR1, then AR2, ..., and then ARn, one could simply mount an argument against all anti-reductionist theories as a set, criticizing features common all individual members of the set. 

So one way to steelman their argument would be to add a premise which states the set of explanations considered are jointly exhaustive.

1. Hypothesis T of the set {T, A1, ..., An} is the best explanation of the evidence E in being superior to its rivals {A1, ..., An} in satisfying the five criteria for explanation candidates.
2. The explanation candidates {T, A1, ..., An} are a jointly exhaustive set.
3. Therefore, other evidence held equal, T is more probable than naturalism.