Consider the following exchange between Christi, a Christian, and Natty, a naturalist, on the problem of evil.

Natty: If God exists, then why is there so much evil and suffering in the world?

Christi: Well, if God exists, it’s logically possible that so much of the evil and suffering in the world is due to the free choices made by humans exercising their free will.

At this point, astute readers will notice that Christi has just invoked the Free Will Defense (FWD). Let’s continue:

Natty: Sure, I guess that’s logically possible. But I wasn’t asking if the existence of so much evil and suffering in the world is logically compatible with God’s existence. Let’s assume that it is compatible. Rather, my question is this. Is the existence of so much evil and suffering in the world strong evidence against God’s existence?

Christi: Why do you say that?

Natty: Let’s take the hypothesis of indifference (HI), which says that nothing in our universe is the result of good or evil supernatural beings acting from outside our universe. Either there are no supernatural beings or, if they do exist, they are indifferent to our suffering.

Christi: Why does HI explain facts about evil and suffering much better than theism does?

Natty: To be precise, HI doesn’t predict facts about evil and suffering, in part because HI doesn’t even predict the existence of conscious or sentient beings capable of suffering. But HI also doesn’t predict the non-existence of evil and suffering. That’s just the kind of hypothesis HI is.

In contrast, theism predicts the non-existence of at least certain kinds of evil and suffering. So you could say that HI ‘negative explains’ facts about those kinds of evil and suffering much better than theism, in the sense that theism predicts the non-existence of those facts whereas HI makes no such prediction at all.

Again, astute readers will notice that Natty has just clarified he is making an evidential argument from evil, one which claims that the hypothesis of indifference explains facts about evil and suffering much better than theism does.

Christi: I’m not so sure I would agree with you about what you call “facts about those kinds of evil and suffering,” but let’s ignore that for now. Your argument presupposes that evil and suffering are, well, evil. But you’re a naturalist. How can you call anything “evil”? And if you can’t call anything “evil,” then how could facts about evil and suffering be any evidence against God’s existence?

Christi is now using a “turnaround” argument, where she tries to turn the tables on Natty and argue that evil is actually evidence for God’s existence.

Natty: By itself, naturalism doesn’t say that certain things like rape, murder, and theft are evil. (Notice also, however, that it doesn’t say that those things are good.) That’s just not what naturalism is about. All naturalism says is that there are no supernatural beings.

Christi: Right, but then how can you, as a naturalist, consistently say that anything is evil? And if you can’t consistently say that anything is evil, how could evil in any way be evidence against God’s existence?

Natty: Let me give you an analogy. Naturalism says nothing about computer viruses and whether anti-virus software is an effective defense against them. It hardly follows that naturalists cannot consistently believe that anti-virus software is an effective defense against viruses. Naturalists can and do believe anti-virus software is an effective defense against viruses, but not because of their naturalism. They believe that for independent reasons, such as personal experience, the universal recommendations of computer security experts, and so forth.

Likewise, just because naturalism doesn’t say anything about evil, it doesn’t follow that naturalists can’t consistently say anything is evil. That would follow if and only if there were no good independent reasons–reasons consistent with naturalism–for saying something is evil.

Christi: Okay, but unlike your computer virus analogy, there is no universal consensus about whether naturalists can believe in objective moral good and evil. Plenty of naturalists don’t.

Natty: True, but the relevant issue is not whether a universal consensus exists, but (1) whether naturalists can consistently believe in objective moral good and evil, and (2) whether the answer to (1) even matters. I do believe there is objective moral good and evil and I think that’s consistent with my naturalism. It’s hard to see how a belief about morality could be logically inconsistent with another belief (naturalism) which says nothing about morality. But let that pass. Let’s assume, for the sake of argument, that naturalism entails there is no objective moral good and evil. Even then, you haven’t given a good reason to reject the argument from evil, since that argument compares theism and HI, not theism and naturalism. But to be charitable, let’s pretend that HI says there is no objective moral good or evil. (It doesn’t say that, but let’s pretend it does.)

Christi: Okay.

Natty: The argument from evil attempts to show that some fact about ‘evil’ (whether it be literal evil or some non-normative concept like pain or suffering) somehow undermines a theistic worldview. We’re assuming, for the sake of argument, that HI entails there is no objective moral good and evil (“nihilism”). How, then, is that supposed to affect the argument?

Christi: Consider the following examples of evil and suffering, such as suffering and death caused by earthquakes, floods, hurricanes, volcanic eruptions, fires, tornadoes, rape, starvation, torture, injury, and disease. Call this list “bad stuff.” We’re agreeing, for the sake of argument, that if HI is true, then “bad stuff” isn’t ‘really’ bad, i.e., “bad stuff” isn’t bad in an objective moral sense.

Natty: Agreed. But this isn’t relevant to evidential arguments from evil, since such arguments don’t require that “bad stuff” be bad in an objective moral sense. All such arguments require is that “bad stuff” happens, which it does. The upshot, then, is that even if HI did entail nihilism, that would do nothing to undermine evidential arguments from evil. We can show this more formally using probabilistic notation. Remember that the crucial premise of my evidential argument from evil is this:

(1) Pr(E | HI) >> Pr(E | T).

Let’s begin by defining a key term.

nihilism =df. The hypothesis that there is no objective moral good and evil.

We can treat your point about objective moral good and evil on HI as an auxiliary hypothesis, namely, that if HI is true, the auxiliary hypothesis nihilism is also true. Using the probability calculus, specifically the Theorem of Total Probability, we can measure the impact of nihilism on (1).

(2) Pr(bad stuff |HI) = Pr(nihilism | HI) x Pr(bad stuff | nihilism & HI) + Pr(~nihilism | HI) x Pr(bad stuff | HI & ~nihilism)

We’ve agreed for the sake of argument that HI entails there is no objective moral good and evil. So Pr(nihilism | HI) = 1 and Pr(~nihilism | HI) = 0. Then the above equation becomes:

(3) Pr(bad stuff |HI) = 1 x Pr(bad stuff | nihilism & HI) + 0 x Pr(bad stuff | HI & ~nihilism)

(4) Pr(bad stuff |HI) = Pr(bad stuff | nihilism & HI)

The crucial premise of my argument becomes:

(1′) Pr(bad stuff | HI & nihilism) >> Pr(bad stuff | T).

This shows that, even granting the controversial claim that HI entails nihilism, the first part of each conditional probability (“bad stuff”) is unchanged. The “HI=nihilism” presupposition does not decrease the value of the first conditional probability and does not increase the value of the second. It follows, therefore, that “HI=nihilism” presupposition does nothing to undermine the claim that the first conditional probability is much greater than the second.