Is a professional group a social group ? For example, is it similar to groups like "lower-class", or not ? What are the differences, for example, between the class of lawyers and what may be called "middle-class" ? I'm working within linguistics about the question of diastratic variation, and we do not make any clear difference between all of these phenomena. Diastratic variation is the social-dependant variation of language. But, intuitively, it seems clear that many phenomena hide behind such a wide definition.