An epistemic possibility is something that might be true, given the available evidence. I might see a bird tomorrow and I might not—given my evidence now, both options are epistemically possible. Not everything is epistemically possible though, as some options are ruled out by my evidence. I’m definitely not on the moon right now (if I were, I’d be suffocating!), so that’s not an epistemic possibility for me.
Epistemic possibilities feature prominently in several arguments about what we know. Suppose, for example, that you’re in a zoo. You’re standing outside the zebra enclosure, and you see an animal that looks exactly like a zebra—horse-like shape, black and white stripes, etc. But then a skeptic comes along and argues as follows:
Maybe that animal is really a mule that has been cleverly disguised to look just like a zebra. So, maybe it’s not a zebra after all. And that means that you don’t really know that it is a zebra.
‘Maybe’ here is an epistemic possibility operator, so the skeptic is pointing out that it is epistemically possible given your evidence that the animal is a mule cleverly disguised to look like a zebra. And this seems true. All of the evidence you have about how the animal looks is just the sort evidence you’d have if it were a mule cleverly disguised to look like a zebra, so that evidence can’t rule out that possibility. From this the skeptic infers that it is also epistemically possible that the animal is not a zebra, and therefore that you do not know that it is a zebra.
Both of those inferences seem sensible, but I think the first one is a mistake. Implausible as it initially sounds, I think it is epistemically possible for you that the animal is a mule cleverly disguised to look like a zebra, but it is not epistemically possible for you that the animal is not a zebra. To see why, consider the following test for epistemic possibility:
If you have a good reason to think that, if a proposition were true, you would have different evidence, then that proposition is not epistemically possible for you. Otherwise, it is.
This test handles standard cases of epistemic possibility well. It is not epistemically possible for me that I am on the moon, says the test, since I have very good reason to believe that I’d have different evidence (e.g. evidence of looking at a grey landscape through a spacesuit helmet) if I were. It is epistemically possible for me that I will see a bird tomorrow, since I have no reason to think that I’d have different evidence than I do if I were going to see a bird tomorrow.
Using this test, we can see why the skeptic’s inference is a bad one. It is epistemically possible for you that the animal is a mule cleverly disguised to look like a zebra, says the test, since you have every reason to believe that you’d have exactly the same evidence if it were. But now think about just the proposition that the animal in the pen is not a zebra. What evidence would you have if that were true? The standard way of answering that question is to think about the most similar scenarios where the animal is not a zebra and what evidence you would have in those scenarios. Plausibly, the most similar scenarios where you’re in a zoo looking at an animal that is not a zebra are just scenarios where you’re looking at some other animal, such as a giraffe or a crocodile. And in those scenarios, you would have very different evidence. So, our test actually says that, even though it is epistemically possible that the animal you’re looking at is a mule cleverly disguised to look like a zebra, it is not epistemically possible that it is not a zebra.
We can apply this thinking to other areas of philosophy with interesting results. The problem of evil is an argument that starts with all of the bad things we observe in the world and concludes that there is no morally perfect, all-powerful God. After all, such a being would surely prevent these bad things unless there was a really good reason to allow them, and there doesn’t seem to be any such reason.
There are many ways of attacking this argument, but one of them, skeptical theism, can be understood as pointing out that we cannot rule out the possibility that there is some reason we haven’t thought of that justifies the bad things we observe. So, the skeptical theist argues:
Maybe God does exist but has some reason beyond our limited understanding of good and evil for allowing all of these bad things to happen. So, God might exist after all. Which means that you don’t know that God does not exist.
This argument has the same form as the skeptic’s argument about the zebra, and it fails for the same reason. It doesn’t follow from the fact that it is epistemically possible that God exists and has a reason for allowing all of the bad things we’ve observed to happen that it is epistemically possible that God exists. We have very good reasons to think that if God existed and had reasons beyond our understanding for allowing the bad things we’ve observed, then we would have just the evidence we do. We’d see all of the same bad things happen, and we’d be just as baffled as to how a morally perfect being could allow them. But what evidence would we expect to have if God existed? That is, what evidence would we have in the most similar scenarios in which God exists? That’s a tough question, in part because scenarios can be similar or dissimilar to each other in different ways. But the answer does not follow from the epistemic possibility that there are reasons beyond our understanding for the evils we’ve observed.
Department of Philosophy