International lawyers have become used to living with the tension between such formal rules as state equality or state sovereignty (it is rarely noted that sovereignty is a formal rule), on the one hand, and the pervasive facts of inequality and power differentials among states, on the other. The usual response is to relegate inequality to the realm of the political and contingent, and to take comfort in the positive values of formal equality, which after all allows for changes in hierarchies of power over time: just as everyone is free to dine at the Ritz, so everyone may aspire to permanent membership of the Security Council, one of international law's few concessions to formal hierarchy.

Dr Simpson's approach is different and strikingly original. No formalist, he sees in the interplay between equality and inequality, between great power and outlaw status, ‘the essence of international law since at least 1815’. International law is a dialogue of power, and its uneven application to different states is fundamental, not accidental. The powerful we will always have with us, and even changes in the cast, or caste, of the powerful will be fewer than we might imagine. And this is not a contingency: formal equality is a device established by the powerful in order to underwrite and prolong their power.