The impossibility of a paretian loyalist

Amartya Sen has argued the impossibility of the Paretian liberal. While his abstract argument is compelling, the concrete significance of the conclusion is in some doubt. This is because it is not clear how important liberalism in his sense is; in particular it is not clear that the sort of liberalism required for the impossibility result is a compelling variety. We show that even if the argument cannot be used to establish the inconsistency of Paretianism and common-or-garden liberalism, it can be adapted to prove a parallel impossibility. This is the impossibility of combining the Pareto criterion with a loyalty constraint involving certain claim-rights rather than liberty-rights. The impossibility of the Paretian loyalist is of interest in itself but it is also interesting for the light it throws on the source of Sen-style impossibilities.