I think the idea of a social contract, as others have sort of hinted at—I'm not sure that they use that language exactly, but I think the idea that interconnected obligations are owed is a good one. Of course, these are consciously entered into, contrary to discussions oftentimes around a social contract, which ignore the fact that a contract by definition is an obligation that's entered into knowingly. But, of course, in this case, people do join clubs and societies—incorporated societies, technically—in a knowing and willing fashion. They do the things that are required to entail membership. They might seek election as an officer on the governing body of the society, and so on.