Julia Galef: Bayes' Rule changed the way I think

Bayes' Rule is a simple formula that tells you how to weigh evidence and change your beliefs. I don't go around plugging numbers into a formula all the time, but nevertheless, becoming familiar with Bayes has shifted the way I think in some important ways.

My beliefs are grayscale - and my confidence in them changes as I learn new things. Well-said, by Julia Galef.

Her example about believing she is a good driver is instructive. A subsequent road accident may require altering that belief, but then again it may not require altering that belief. Galef's point is that we cannot stop at a superficial review of an incident or event vis-a-vis some preexisting belief. Instead, we need to probe more deeply into such incident or event, and determine its cause.

If the accident were purely another driver's fault (e.g. misjudgment, carelessness), then she can viably maintain her belief that she is a good driver. However, if the accident were entirely her own fault, she may still have good reason to hold to her belief. For example, if she had a five-year history of driving with no accidents, a one-off accident now doesn't necessarily mean she is suddenly a bad driver. But, to her point, that one-off accident may prompt even a minute decrease in her confidence in that belief. Of course, repeated driving mistakes, resulting in frequent accidents may require significant alteration or dismissal of her belief: that is, she is no longer a good driver; she is a bad driver.

There is a name for beliefs that people hold as true, no matter the reality surrounding them, no matter a raft of opposing evidence: dogma. Bayes' Theorem or Bayes' Rule is an antidote :)