Why is it not possible to compare utility across individuals?
Is this only impossible when we consider ordinal utility where we have no numerical unit?
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Sign up to join this communityWhy is it not possible to compare utility across individuals?
Is this only impossible when we consider ordinal utility where we have no numerical unit?
Whether `interpersonal comparisons of utility' are possible depends on what you mean by 'utility':
Why are interpersonal utility comparisons not possible
They are not impossible. Instead, whether or not interpersonal utility comparisons are possible is merely an opinion. (In the language of the positive-normative dichotomy, any claims as to whether or not such comparison are possible is a normative one.)
The standard/orthodox approach taken in pure microeconomic theory is that the assumption of interpersonal utility comparisons is not necessary (to get many results in microeconomic theory). We thus make no such assumption (without necessarily making the dogmatic claim that such comparisons are impossible).
However, the actual approach taken by economists who want to say anything about the real world or do any welfare economics—in other words, most economists—is that we can and do make interpersonal utility comparisons.
Correct this is impossible only with ordinal utility with cardinal utility you can make interpersonal comparisons.
The reason why you can’t do it with ordinal utility intuitively is that with ordinal utility that there is no measurable utility that individual derived from some good. Under ordinal utility you can only say that Lisa prefers ice cream to cereal, but you can’t say that she derives let’s say twice as big utility $u$(cerial)=10 and $u$(ice cream)=20. The same holds between people if there is Margaret who also prefers ice cream to cereal it does not mean they have the same utility. Their utility of ice cream and cereal could be same, greater or lower and all this would still be consistent with saying they both prefer ice cream to cereal.
However, with cardinal utility you can say that some person, let’s say Margaret, derived 30 utils from ice cream and Lisa derived just 20 utils so Margaret prefers ice cream more.