In sum, Jean Carbonnier established at the same time a clear and understandable sociological theory for jurists, as well as a legal theory within the reach of sociologists. This synthesis between law and sociology allowed the usage of sociological methods of investigation, thereby breaking with the "rational" tradition in French legislation. These methods include the opinion poll (IFOP, then INED) and field research in order to measure the "demand for law" expressed by citizens. This allowed notably the establishment of divorce by mutual consent (1975), at a time when divorce by fault was the only form offered to divorcing couples.