Rawls's difference principle contains a certain normative ambiguity, so that opposing
views, including strong inegalitarian ones, might find a home under it. The element
that introduces this indeterminacy is the absence of an explicit reference to
time. Thus, a society that agrees on the difference principle as the
proper justification of basic political-economic institutions, might nevertheless
disagree on whether their specific institutions are justified by that principle.
Such disagreement would most often centre on issues of fact: will a more egalitarian
policy in fact prioritize the least well off or will a more libertarian
policy do so? But facts are not the only possible points of contention. According to
the fundamental indeterminacy, considering merely the sum of advantages to the least
well off, the difference principle is indifferent among different flows of equal
income over time. It cannot adjudicate among more or less unequal distributions
across social groups when the sum income of the least advantaged group is constant.
The fundamental indeterminacy lies at the bottom of three derivative
indeterminacies: an adequate future discount rate, an acceptable absolute minimum,
and a reasonable time interval. These might form the basis of political disagreement
among self-proclaimed endorsers of the difference principle of left and right over
the way the principal social-economic institutions ought to be structured and the
distributions that ensue.
