In “The problem of social cost” (1960), Ronald H. Coase argued that what are exchanged are property rights and that the operation of the price system requires these rights to be defined. Coase was more interested in how property rights are (or should be) allocated and exchanged than in their content or definition. He insisted that factors of production must be considered as property rights, but conversely, property rights, even when they relate to nuisances, are nothing more than extra production costs.