Groups secure advantages by restricting access to them, using credentials, licensing, property or membership rules that look like quality control.
Weber named the process and Parkin developed it in 1979 into a general account of stratification: the interesting question about an advantaged group is not what it possesses but what it excludes others from. Because the restriction is almost always justified on grounds of standards, closure and quality assurance are empirically hard to separate, and often the same act.
In practice
- A profession that raises its entry qualification improves standards and reduces competition, and the two cannot be distinguished from the outside.
- A club that requires two existing members as proposers will resemble itself in twenty years.