The title and the job : the relationship between the system of production and the system of reproduction. All the surveys of mobility, all the historical comparisons consider as out of the question what must be the central object of inquiry -that is, the permanence of the relationship between the words and the things, between the titles and the jobs, between the nominal and the real. What sense is there in considering as identical the primary school teacher of 1880 and the primary school teacher of 1930, or of 1974 ? Is the son of a primary school teacher really a "teacher's son" in the sense that he is himself a teacher ? Doesn't the nominal identity hide the real disparity ? The dialectic of title and job is a manifestation of the dialectic of de-classifying and re-classifying that is one aspect of the class struggle.