If you were trying to assess a person’s rationality on the basis of one not-directly-verbal indicator, given his or her behavior over the course of a meal, what would it be?
And if you could ask only one question of a person, to assess his or her rationality, which question would it be?
That’s from me! As for the first benchmark, you cannot refer to verbal answers to questions you might ask. You could however nominate “the person hesitated for a long time before answering each question,” or something similar along the behavioral dimension. That is what I mean by “not-directly-verbal.”
Part of me wishes to suggest “are they carrying a book or not?”, but alas too many semi-rational people don’t do that. I might consider the process by which they select a menu item and order their food, as a kind of proxy for decision-making more generally. How well they treat the server would be another variable of interest.
As for the second question, I suggest asking the person who he or she thinks are the rational people. If the answer is considered and uncertain and complex, upgrade the rationality of that person. If the answer is dogmatic and refers to holding a particular doctrine…
I considered asking the person if he is himself rational, but that simply will induce lying and false modesty.
Can you think of better tests?