How to Be Irrational

Here, I explain how a person can have a belief that is internally unjustified.*

[ *Based on: “How to Be Irrational,” pp. 94-108 in Seemings: New Arguments, New Angles, ed. Scott Stapleford, Kevin McCain, and Matthias Steup (Routledge, 2024). ]

1. The Puzzle

I have argued that appearances (states of something’s seeming to us to be the case) are the source of all justification. This view makes it very easy to have justified beliefs; you can right away see how beliefs about the external world, the past, other minds, morality, and other things are justified (all things that epistemologists have struggled to account for). Yay!

One concern about this view is that it may make it too easy to have justified beliefs; indeed, it makes it puzzling how one could ever have an unjustified belief. Do we sometimes believe things that don’t even seem true to us? Why would anyone—or indeed, how could anyone—do that? Or maybe we believe things that seem true, but we have defeaters that we are ignoring. But if (as I also hold) these defeaters would themselves have to come from other appearances, then why would someone ignore these defeaters? If the defeater-appearance is strong enough to defeat the justification for P, then why isn’t it strong enough to defeat the psychological inclination to accept P?

Let’s try to figure that out.

2. Forms of Irrationality

First, we should distinguish credences from outright beliefs. Credences are degrees of confidence, which can be represented by real numbers between 0 and 1. Outright beliefs are qualitative states (you either believe or don’t). However high your credence in X is (short of 100%), there is always an additional question of whether such a credence is enough, in the circumstances, for you to take the qualitative step of outright believing X. The threshold level of probability needed to outright believe something can vary depending on the subject matter and the circumstances, including pragmatic factors.

There are three ways of being epistemically irrational:

1. Having a credence higher (/lower) than the evidence warrants.

2. Having (/lacking) an outright belief when the probability is below (/above) the appropriate threshold for justified outright belief.

3. Violating obligations regarding the appropriate conduct of inquiry.

#3 is interesting. I have in mind obligations like this: Maybe you’re obligated, before forming a belief about a controversial issue, to listen to both sides of the issue. Maybe