Vivek Haldar

Rational Equivalence

There is an implicit rule that most technical and engineering people grow into over the course of their education. But even though it is implicit, it is strong. Its violation causes great confusion. Most are confounded enough that instead of reconciling the violation they simply learn to accept it, and move on with life.

What is this rule? I’m going to call it the principle of rational equivalence: two rational people, given the same set of facts, must arrive at identical conclusions.

Of course, this is nothing but a fuzzy extension of modus ponens, the very bedrock of logic.

And of course, this is violated all the time in the real world. People see a situation, which presumably is objectively invariant, and yet arrive at completely opposing conclusions.

They are many explanations for the violation of rational equivalence (people are not rational, the facts are incorrectly perceived, or even if people are rational and the facts are correctly percieved, they make mistakes of logic etc etc), but every time it happens it still confounds most rational technical people. It’s a cognitive blind spot. It’s like one of those false proofs of something absurd where you know the result can’t be true, yet every step seems legit.