A new paper by philosophers Dominik Klein and Matteo Colombo, forthcoming in the journal Episteme, defines a mystery as something that cannot be explained.
This definition doesn't stray too far from our everyday usage. The first definition of mystery to appear on a Google search, for example, is "something that is difficult or impossible to understand or explain."
But on Klein and Colombo's view, to declare something a mystery isn't just a confession of ignorance. Some of the time, you can learn something important when you learn that something is a mystery — provided it's the right kind of mystery.
To argue for this conclusion, Klein and Colombo developed a partial taxonomy of mysteries. The key distinction is between symmetrical and asymmetrical mysteries.
A mystery is symmetrical if its negation is just as unexplainable as the initial mystery itself. To use their example, suppose you learn that there is more landmass on the northern hemisphere than on the southern hemisphere. And suppose you ask "why?" — only to learn, from a sincere and reliable expert, that it's a mystery. It's not just that we don't know now, it's that it's in principle unexplainable. If this is all true, then it seems that the negation of the mystery — the claim that there is not more landmass on the northern hemisphere than on the southern hemisphere — would be equally mysterious. The mystery would be symmetrical.
By contrast, consider the mystery of how Jesus converted water into wine, or the mystery of how something could arise from nothing, or the mystery of how the physical mind could give rise to something that is (some might claim) non-physical. These mysteries are asymmetrical. Were it the case that Jesus did not convert water into wine, the mystery would vanish. Were it the case that something couldn't arise from nothing, the mystery would vanish. Were it the case that the physical mind didn't give rise to something non-physical, the mystery would vanish. It's in this sense that the mysteries are asymmetrical.
Klein and Colombo have different diagnoses for symmetrical and asymmetrical mysteries. Whereas the former might reflect genuine limits to our understanding, the latter suggest a mismatch between one side of the mystery and our existing commitments about the way the world works and about what counts as a legitimate explanation. And that, they argue, has interesting implications for how we should revise our beliefs when we learn that something is an (asymmetrical) mystery.
Klein and Colombo develop their argument more formally, but the basic intuition is this: When you learn that some proposition P (say, that Jesus turned water into wine) is a mystery, you learn that there is a mismatch between P and existing commitments about the way the world works and about what counts as a legitimate explanation. In light of that mismatch, something has to give. You should reduce your belief that P is the case, revise your existing commitments, or both. On the assumption that you have good reason to believe your existing commitments and also good reason to believe that P, but that neither is 100 percent certain, both beliefs should shift in response to the mismatch, at least a bit. Concretely: Learning that how Jesus turned water into wine is a mystery should make you at least a smidge less confident that the event actually occurred.
If it seems unintuitive that a failure to explain should count as evidence against some proposition, consider the reverse. If we have a very good explanation for some proposition P, shouldn't that make you more inclined to believe that P? Not all philosophers agree that it should, but psychological evidence supports the idea that people in fact use the existence and quality of an explanation as a guide to what's true.
Just as explaining a good joke can rob it of some humor, explaining the mysterious might rob it of some mystique. But if Klein and Colombo's analysis is correct, we should be on the lookout for what is and isn't explainable. And we should be drawn to the mysterious — not only because it marks the limits of our understanding, but because we can (sometimes) learn something from the unexplainability itself.
Tania Lombrozo is a psychology professor at the University of California, Berkeley. She writes about psychology, cognitive science and philosophy, with occasional forays into parenting and veganism. You can keep up with more of what she is thinking on Twitter: @TaniaLombrozo