Metasociology concerns itself with "the methodological considerations necessary for carrying out sociological research, constructing sociological systems and criticizing such research and systems after they have been completed". The domain of metasociology extends beyond methodological considerations, or standards for appropriate theory. At least four alternative metasociological stances have been offered. The first is the biological model; the second is the natural science model; the third, never systematically articulated, is the social science model; and the fourth is a model taken from the humanities. Each model has its own bundle of metaphors and values, and each represents differing role models the sociologist may emulate. The metaphor is chiefly a tool for revealing special properties of an object or event. Frequently theorists forget this and make their metaphors a real entity in the empirical world. There are at least five levels of theory-work: ad hoc classificatory systems; categorical systems or taxonomies; conceptual frameworks; theoretical systems; and empirical-theoretical systems.