The Logic Of Skepticism
Introduction (Via Rationally Speaking)
Being a skeptic is a rather lonely art. People often confuse you for a cynic, and I’m not using either term in the classical philosophical sense, of course. In ancient Greece, the cynics were people who wished to live in harmony with nature, rejecting material goods (the root of the word means “dog-like,” and there are various interpretations as to its origin). The Western equivalent of Buddhist monks, if you will. The skeptics, on the other hand, were philosophers who claimed that since nothing can be known for certain the only rational thing to do is to suspend judgment on everything. That’s not what I’m talking about.
A skeptic in the modern sense of the term, let’s say from Hume forward, is someone who thinks that belief in X ought to be proportional to the amount of evidence supporting X. Or, in Carl Sagan’s famous popularization of the same principle, extraordinary claims require extraordinary evidence. In that sense, then, what I will call positive skeptics do not automatically reject new claims, they weigh them according to the evidence. And of course we aren’t cynics in the modern sense of the term either, i.e. we don’t follow Groucho Marx when he famously said “Whatever it is, I’m against it!” (Of course, he was joking, though that seems to be the motto of the current Republican party.)
Excerpt (Via Rationally Speaking)
What’s that got to do with skepticism? Whenever confronted with a new claim, it’s reasonable to think that the null hypothesis is that the claim is not true. That is, the default position is one of skepticism. Now the tricky part is that type I and type II errors are inversely proportional: if you lower your threshold for one, you automatically increase your threshold for the other (there is only one way out of this trade-off, and that’s to do the hard work of collecting more data). So if you decide to be conservative (statistically, not politically), you will raise the bar for evidence, thereby lowering the chances of rejecting the null hypothesis and accepting the new belief when it is not in fact true. Unfortunately, you are also simultaneously increasing your chances of accepting the null and rejecting the new belief when in fact the latter is true.