It is one of the paradoxes in which law, including international law, abounds that it is often the most fundamental problems that are the least studied. As in life, it seems that we can get by with the day- to- day business of a legal system without answering many of the big questions, focusing instead on specific rules and their application to the facts before us. This may explain in part why, despite their existence for over two hundred years, their significance for international relations for over a hundred, and their overwhelming numerical predominance today relative to states, we still lack an agreed understanding of what international organizations are, even when we confine ourselves to intergovernmental organizations. Various definitions exist, but Lorenzo Gasbarri’s concern is less the definition of an international organization than how we conceive of such organizations as phenomena. His implicit point, moreover, is that we cannot in fact get by, at least coherently, with the day- to- day business of the law of international organizations, applying specific rules to the facts before us, without an adequate common conception of an international organization.