When a person testifies about some past event, and his or her listeners have no external evidence to corroborate or refute that testimony, those listeners will place a great deal of emphasis on credibility. “I find her a very credible witness.” “I just didn’t find him credible.” We know that con men make opulent livings through seeming credible to large numbers of people; if we search our memories we will discover scenes in which we believed people we shouldn’t have believed and disbelieved people we should have believed; but in the moment we human beings seem to have a nearly absolute confidence in our ability to assess credibility.

This is, of course, complete nonsense. None of us has the superpower of looking into speakers’ souls to discern their true character. Each of us is, in many circumstances, easily fooled. And perhaps on some level, somewhere deep in the recesses of our minds, we realize this. We remember those moments when we were so sure someone was lying when they weren’t, or telling the truth when they weren’t. So we peek around at our ingroup for confirmation. And we get it. They have the same impressions, the same feelings, the same assessments of credibility.

And that can scarcely be surprising, because we share our prejudices and presuppositions and assumptions and tendencies with other members of our ingroup — that’s in large part what makes them our ingroup. So tribalism both produces our impressions of credibility and confirms them. Which makes our impressions of credibility epistemically worthless.

But without them, what do we have? That’s a question that, it seems, few are willing to face. To doubt our impressions is to doubt much of what sustains us day by day. This morning Ross Douthat writes, “Only the Truth Can Save Us Now.” Yeah, good luck with that.

how to evaluate a strong but disputable claim

This from John D. Cook is a great example of how to respond to strong but highly disputable scientific claims — in this case Michael Atiyah’s claim to have proven the Riemann hypothesis:

Atiyah’s proof is probably wrong, just because proofs of big theorems are usually wrong. Andrew Wiles’ proof of Fermat’s Last Theorem had a flaw that took a year to patch. We don’t know who Atiyah has shown his work to. If he hasn’t shown it to anyone, then it is almost certainly flawed: nobody does flawless work alone. Maybe his proof has a patchable flaw. Maybe it is flawed beyond repair, but contains interesting ideas worth pursuing further.

The worst case scenario is that Atiyah’s work on the fine structure constant and Todd functions is full of holes. He has made other big claims in the last few years that didn’t work out. Some say he should quit doing mathematics because he has made big mistakes.

I’ve made big mistakes too, and I’m not quitting. I make mistakes doing far less ambitious work than trying to prove the Riemann hypothesis. I doubt I’ll ever produce anything as deep as a plausible but flawed proof of the Riemann hypothesis.

Fantastic. Would that we had more people who think this way.

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