Rationalism is most often characterized as an epistemological position. On this view, to be a rationalist requires at least one of the following: (1) a privileging of reason and intuition over sensation and experience, (2) regarding all or most ideas as innate rather than adventitious, (3) an emphasis on certain rather than merely probable knowledge as the goal of enquiry. -- The Stanford Encyclopedia of Philosophy on Continental Rationalism.

By now, there are some things which most Less Wrong readers will agree on. One of them is that beliefs must be fueled by evidence gathered from the environment. A belief must correlate with reality, and an important part of that is whether or not it can be tested - if a belief produces no anticipation of experience, it is nearly worthless. We can never try to confirm a theory, only test it.

But yet, we seem to have no problem coming up with theories that are either untestable or that we have no intention of testing, such as evolutionary psychological explanations for the underdog effect.

I'm being a bit unfair here. Those posts were well thought out and reasonably argued, and Roko's post actually made testable predictions. Yvain even made a good try at solving the puzzle, and when he couldn't, he reasonably concluded that he was stumped and asked for help. That sounds like a proper use of humility to me.

But the way that ev-psych explanations get rapidly manufactured and carelessly flung around on OB and LW has always been a bit of a pet peeve for me, as that's exactly how bad evpsych gets done. The best evolutionary psychology takes biological and evolutionary facts, applies those to humans and then makes testable predictions, which it goes on to verify. It doesn't take existing behaviors and then try to come up with some nice-sounding rationalization for them, blind to whether or not the rationalization can be tested. Not every behavior needs to have an evolutionary explanation - it could have evolved via genetic drift, or be a pure side-effect from some actual adaptation. If we set out by trying to find an evolutionary reason for some behavior, we are assuming from the start that there must be one, when it isn't a given that there is. And even a good theory need not explain every observation.