On Admitting There Might Be Some Evidence for the Other Side

Note: I thought I had blogged this before, but a quick search didn’t turn anything up.
Have you ever noticed how rare it is for a person to admit there might be any evidence against their position, at least (or especially) when it comes to religion? I think this should make people suspicious about whether their cognitive biases are playing a larger role than they might like to admit.
People can mean different things by “evidence.” Solely for the sake of discussion, I’m going to define “evidence” in this post to mean “some fact which is more probable on the assumption that one hypothesis is true than it is on the assumption that another hypothesis is true.” In mathematical symbols, where E is evidence, H1 is one hypothesis , and H2 is a contradictory hypothesis, this means that E is evidence for H1 just in case Pr(E|H1) is greater than Pr(E|H2).
Let’s conduct a thought experiment. Without knowing what H1 and H2 are, assume that both are coherent (i.e., they don’t contradict themselves in the way “There are married bachelors” would) and that H1 is true.
Now ask yourself this question.

Q: “Assuming H1 is true, why does it follows that there is no (zero) evidence against H1 and for H2?”

Using the definition of “evidence” I’ve provided in this post, the correct answer is this.

A: “It doesn’t follow at all. It’s possible that there is some evidence, however small, against H1 and for H2 and that evidence is outweighed by other evidence, evidence which more strongly favors H1 over H2.”

Now let’s apply this insight to competing worldviews like theism and naturalism. Based upon the answer I just provided, it should be obvious that

(1) If theism is true, there could be evidence against theism and for naturalism.

and:

(2) If naturalism is true, there could be evidence naturalism and for theism.

I think it’s no small coincidence that Christian philosopher Richard Swinburne, who takes a similar Bayesian approach to evidence, thinks the total evidence favors God’s existence, but evil and suffering provides evidence against God’s existence.

“So, given both of these additional hypotheses, and conscious of the very short temporal span of human and animal life (and to a lesser extent of the limits of pain and suffering within that life that can be experienced), my own final verdict is that a God would not need to be less than perfectly good if he were to bring it about or allow to occur that amount of suffering that exists for the sake of the greater good that results. Still, the need for additional hypotheses in order to save theism makes the resulting theistic theory more complicated than theism on its own (bare theism), and so reduces the probability of bare theism. Put another way, bare theism makes it less probable that we would find evil of as great a degree as we do than it would be on background evidence alone, because theism is compatible with the evidence only if we add to theism a further hypothesis or hypotheses. Hence, evil provides a good C-inductive  argument against the existence of God. But it does not provide a very strong one, for the reason that providing life after death for many humans (not merely those who need compensation) and becoming incarnate to share their suffering are the kinds of acts that a good God might well do anyway–for they are good acts (and perhaps good acts of different kinds from the other acts of God that we have been discussing, and maybe even acts of best kinds), whether or not required in order for God justifiably to allow the amount of evil that occurs. … So, with e as the occurrence of the moral and natural evils known to us, h as the hypothesis of theism, and k as the background evidence considered in previous chapters, P(h|e&k) < P(h|k), but the former is not less than the latter by very much.”
Richard Swinburne, The Existence of God (second ed., New York: Oxford University Press, 2004), 265-66.

I happen to disagree with Swinburne’s assessment of the strength of the evidence from evil, but that really doesn’t matter. With a clear (and rigorous) use of probability theory, Swinburne agrees that evil provides objective evidence against God’s existence.
Swinburne isn’t the only theist who admits this. Off the top of my head, I think I remember reading that philosophers Gregory E. Ganssle and Victor Reppert do as well. There are probably others.
Similarly, on the naturalist side, I’ve defended an argument from consciousness which says that consciousness is more probable on theism than on naturalism.
The moral here, I think, is that we should be skeptical whenever someone claims there is no (zero) evidence for something. Perhaps that is why the great philosopher Bertrand Russell, when asked what he would say to God after he dies if it turns Russell was wrong and God exists, is reported to have answered, “Not enough evidence, God! Not enough evidence!” He didn’t say, “No evidence, God! No evidence!” Instead, he said, “Not enough evidence.”

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