Interpersonal level comparability implies comparability of utility differences

It is generally believed that the possibility of making interpersonal comparisons of utility levels (as required, e.g.,in applying the Rawlsian maximin criterion) does not require interpersonal comparison of utility differences (which involve cardinal utilities). Thus, if we are confined to level comparability, it is believed that no cardinal utility need be involved. Here, I wish to show that, with some very general conditions, the general possibility of interpersonal comparison of utility levels implies interpersonal comparison of utility differences (or unit comparability, with suitablescaling). Thus,the sufficiency of ordinalism is a mistaken belief.