I think the main difference between the marginal reversal test and how I read your post is just the magnitude of the change. For the marginal reversal test to make sense, I think the change needs to be small relative to “typical” values of the parameter. So, changing life spans by months rather than years, or changing body temperature by single degrees.
And yeah, I think that the counterfactual reversal test is much more of a heuristic than a careful argument, but it does seem useful as a way of disentangling disagreements, especially with sufficiently thoughtful interlocutors.
I think the main difference between the marginal reversal test and how I read your post is just the magnitude of the change. For the marginal reversal test to make sense, I think the change needs to be small relative to “typical” values of the parameter. So, changing life spans by months rather than years, or changing body temperature by single degrees.
And yeah, I think that the counterfactual reversal test is much more of a heuristic than a careful argument, but it does seem useful as a way of disentangling disagreements, especially with sufficiently thoughtful interlocutors.