‘Ordinalism’ is the view that information about people’s well-being can only derive from people’s preferences. Most ordinalists believe this theory rules out interpersonal comparisons of well-being. However, some ordinalists disagree; they argue that interpersonal comparisons can be based on ‘extended preferences’, which are the preferences a person has between alternative lives, together with the personal characteristics of a person living those lives. This paper shows their arguments are mistaken. Ordinalism really is incompatible with interpersonal comparisons of well-being. This constitutes a reductio ad absurdum of ordinalism. This paper suggests an alternative basis for interpersonal comparisons
