In “The Bottom Line,” I presented the dilemma of two boxes, only one of which contains a diamond, with various signs and portents as evidence. I dichotomized the curious inquirer and the clever arguer. The curious inquirer writes down all the signs and portents, and processes them, and finally writes down, “Therefore, I estimate an 85% probability that box B contains the diamond.” The clever arguer works for the highest bidder, and begins by writing, “Therefore, box B contains the diamond,” and then selects favorable signs and portents to list on the lines above.

The first procedure is rationality. The second procedure is generally known as “rationalization.”

“Rationalization.” What a curious term. I would call it a wrong word. You cannot “rationalize” what is not already rational. It is as if “lying” were called “truthization.”

On a purely computational level, there is a rather large difference between:

Starting from evidence, and then crunching probability flows, in order to output a probable conclusion. (Writing down all the signs and portents, and then flowing forward to a probability on the bottom line which depends on those signs and portents.)
Starting from a conclusion, and then crunching probability flows, in order to output evidence apparently favoring that conclusion. (Writing down the bottom line, and then flowing backward to select signs and portents for presentation on the lines above.)

What fool devised such confusingly similar words, “rationality” and “rationalization,” to describe such extraordinarily different mental processes? I would prefer terms that made the algorithmic difference obvious, like “rationality” versus “giant sucking cognitive black hole.”

Not every change is an improvement, but every improvement is necessarily a change. You cannot obtain more truth for a fixed proposition by arguing it; you can make more people believe it, but you cannot make it more true. To improve our beliefs, we must necessarily change our beliefs. Rationality is the operation that we use to obtain more accuracy for our beliefs by changing them. Rationalization operates to fix beliefs in place; it would be better named “anti-rationality,” both for its pragmatic results and for its reversed algorithm.

“Rationality” is the forward flow that gathers evidence, weighs it, and outputs a conclusion. The curious inquirer used a forward-flow algorithm: first gath...

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