The “substitution principle” isn’t as trivial as both of you conclude. The claim is that an easier to answer question is substituted for the actual question when System 1 can’t answer the harder question. That’s not the same as saying a simplifying heuristic is involved. The difference is that to accord with the substitution principle, you simplify the question, which you then use valid means to ascertain. In the case of generic heuristic substitution, you use a heuristic that may not answer any plausible question—except as an approximation. The “substitution principle” constrains the candidate heuristics further (by limiting them to exact answers to substituted questions) than do ordinary heuristics. The “substitution principle” is an elegant theory, although don’t know whether it’s true. (I haven’t read Kahnemann’s newest book.)
The “substitution principle” isn’t as trivial as both of you conclude. The claim is that an easier to answer question is substituted for the actual question when System 1 can’t answer the harder question. That’s not the same as saying a simplifying heuristic is involved. The difference is that to accord with the substitution principle, you simplify the question, which you then use valid means to ascertain. In the case of generic heuristic substitution, you use a heuristic that may not answer any plausible question—except as an approximation. The “substitution principle” constrains the candidate heuristics further (by limiting them to exact answers to substituted questions) than do ordinary heuristics. The “substitution principle” is an elegant theory, although don’t know whether it’s true. (I haven’t read Kahnemann’s newest book.)