Credence-First Skepticism

Philosophers usually treat skepticism as a thesis about knowledge. The skeptic about X holds that people who claim to know X don't in fact know X. Religious skeptics think that people who say they know that God exists don't in fact know that. Skeptics about climate change hold that we don't know that the planet is warming. Radical philosophical skepticism asserts broad failures of knowledge. According to dream skepticism, we don't know we're not dreaming. According to external world skepticism, we lack knoweldge about the world beyond our own minds.

Treating skepticism as a thesis about knowledge makes the concept or phenomenon of knowledge crucially important to the evaluation of skeptical claims. The higher the bar for knowledge, the easier it is to justify skepticism. For example, if knowledge requires perfect certainty, then we can establish skepticism about a domain by establishing that perfect certainty is unwarranted in that domain. (Imagine here the person who objects to an atheist by extracting from the atheist the admission that they can't be certain that God doesn't exist and therefore they should admit that they don't really know.) Similarly, if knowledge requires knowing that you know, then we could establish skepticism about X by establishing that you can't know that you know about X. If knowledge requires being able to rule out all relevant alternatives, then we can establish skepticism by establishing that there are relevant alternatives that can't be ruled out. Conversely, if knowledge is cheaper and easier to attain -- if knowledge doesn't require, for example, perfect certainty, or knowledge that you know, or being able to rule out every single relevant alternative -- then skepticism is harder to defend.

But we don't have to conceptualize skepticism as a thesis about knowledge. We can separate the two concepts. Doing so has some advantages. The concept of knowledge is so vexed and contentious that it can become a distraction if our interests in skepticism are not driven by an interest in the concept of knowledge. You might be interested in religious skepticism, or climate change skepticism, or dream skepticism, or external world skepticism because you're interested in the question of whether god exists, whether the climate is changing, whether you might now be dreaming, or whether it's plausible that you could be radically mistaken about the external world. If your interest lies in those substantive questions, then conceptual debates about the nature of knowledge are beside the point. You don't want abstract disputes about the KK principle to crowd out discussion about what kinds of evidence we have or don't have for the existence of God, or climate change, or a stable external reality, and how relatively confident or unconfident we should be in our opinions about such matters.

To avoid distractions concerning knowledge, I recommend that we think about skepticism instead in terms of credence -- that is, degree of belief or confidence. We can contrast skeptics and believers. A believer in X is someone with a relatively high credence in X, while a skeptic is someone with a relatively low credence in X. A believer thinks X is relatively likely to be the case, while a skeptic regards X as relatively less likely. Believers in God find the existence of God likely. Skeptics find it less likely. Believers in the external world find the existence of an external world (with roughly the properties we ordinarily think it has) relatively likely while skeptics find it relatively less likely.

"Relatively" is an important word here. Given that most readers of this blog will be virtually certain that they are not currently dreaming, a reader who thinks it even 1% likely that they're dreaming has a relatively low credence -- 99% instead of 99.999999% or 100%. We can describe this as a moderately skeptical stance, though of course not as skeptical as the stance of someone who thinks it's 50/50.

[Dall-E image of a man flying in a dream]

Discussions of radical skepticism in epistemology tend to lose sight of what is really gripping about radically skeptical scenarios: the fact that, if the skeptic is right, there's a reasonable chance that you're in one. It's not unreasonable, the skeptic asserts, to attribute a non-trivial credence to the possibility that you are currently dreaming or currently living in a small or unstable computer simulation. Whoa! Such possibilities are potentially Earth-shaking if true, since many of the beliefs we ordinarily take for granted as obviously true (that Luxembourg exists, that I'm in my office looking at a computer screen) would be false.

To really assess such wild-seeming claims, we should address the nature and epistemology of dreaming and the nature and epistemology of computer simulations. Can dream experiences really be as sensorily rich and realistic as the experiences that I'm having right now? Or are dream experiences somehow different? If dream experiences can be as rich and realistic as what I'm now experiencing, then that seems to make it relatively more reasonable to assign a non-trivial credence to this being a dream. Is it realistic to think that future societies could create vastly many genuinely conscious AI entities who think that they live in worlds like this one? If so, then the simulation possibility starts to look relatively more plausible; if not, then it starts to look relatively less plausible.

In other words, to assess the likelihood of radically skeptical scenarios, like the dream or simulation scenario, we need to delve into the details of those scenarios. But that's not typically what epistemologists do when considering radical skepticism. More typically, they stipulate some far-fetched scenario with no plausibility, such as the brain-in-a-vat scenario, and then ask questions about the nature of knowledge. That's worth doing. But to put that at the heart of skeptical epistemology is to miss skepticism's pull.

A credence-first approach to skepticism makes skepticism behaviorally and emotionally relevant. Suppose I arrive at a small but non-trivial credence that I'm dreaming -- a 0.1% credence for example. Then I might try some things I wouldn't try if I had a 0% or 0.000000000001% credence I was dreaming. I might ask myself what I would do if this were a dream -- and if doing that thing were nearly cost-free, I might try it. For example, I might spread my arms to see if I can fly. I might see if I can turn this into a lucid dream by magically lifting a pen through telekinesis. I'd probably only try these things if I had nothing better to do at the moment and no one was around to think I'm a weirdo. And when those attempts fail, I might reduce my credence that this is a dream.

If I take seriously the possibility that this is a simulation, I can wonder about the creators. I become, so to speak, a conditional theist. Whoever is running the simulation is in some sense a god: They created the world and presumably can end it. They exist outside of time and space as I know them, and maybe they have "miraculous" powers to intervene in events around me. Perhaps I have no idea what I could do that might please or displease them, or whether they're even paying attention, but still, it's somewhat awe-inspiring to consider the possibility that my world, our world, is nested in some larger reality, launched by some creator for some purpose we don't understand. If I regard the simulation possibility as a live possibility with some non-trivial chance of being true, then the world might be quite a bit weirder than I would otherwise have thought, and very differently constituted. Skepticism gives me material uncertainty and opens up genuine doubt. The cosmos seems richer with possibility and more mysterious.

We lose all of this weirdness, awe, mystery, and material uncertainty if we focus on extremely implausible scenarios to which we assign zero or virtually zero credence, like the brain-in-a-vat scenario, and focus our argumentative attention only on whether or not it's appropriate to say that we "know" we're not in those admittedly extremely implausible scenarios.