Sociology is by nature an interdisciplinary field, it is closely linked to other social sciences; but it has a particular connection to psychology : since social systems include individuals, sociology includes psychology (like physics include chemistry or biology includes psychology); it’s an ontological inclusion, not a disciplinary one, but it entails that both disciplines should be compatible. Such is not the case, though ; in fact, sociologists make little use of psychological knowledge ; they often deal with an « ideal-typical » individual, which is a kind of abstract individual. The reason why they use little knowledge concerning real individuals has to do with the the history of both disciplines, with hyper-specialization and university enclosures. Psychologists, in turn, although sometimes interested in the social environment of individuals, have hardly any care and any use for institutions and the reasons why individuals act as members of social systems. Useless to say that both disciplines should be better linked.