This essay does not deal with the matter of Celtic and Germanic peoples as such, but with that of the historical production of their difference from the point of view of the historians. Such difference cannot for sure be considered anything pertaining to their essence, more or less in terms of racial features, however in terms of the unavoidable upshot of the social processes having taken place before their encounter and afterwards determined by this same encounter – as well as by the manner historians have bestowed validity to the presentation of such social production. However, this difference production is obviously not merely observed at the level of whole peoples such as the Celtic or Germanic ones: it is a multiscalar process that is characteristic of the production of the social itself, from the scale of the individual to the scale (by our time) of mankind – therefore, a general process of sociogenesis. This is what leads me to re-examine the sense of what the French medievalist Marc Bloch affirmed in 1937 and afterwards, that History is defined, above all, as a science of difference. Nevertheless, for a long time, this matter of the difference has not been taken seriously from the point of view of the historians (particularly the medievalists): it was merely observed in order to grant the impression of a medieval society which was simply heterogeneous, diverse, variable, incoherent, subject to exogenous factors (climate accidents, invasions, gold incomes, pandemics, technical contributions, cultural influences etc.) or to collective intentionalities (kings, popes, knights, peoples, etc.). Since a certain amount of time, yet, the idea of a society the dynamics of which derives precisely from the multiple scale articulation (from the village to Christianity) of both material and ideal contrasts emerges – contrasts which are not at all to be eliminated, including at the level of the global speech (in opposition to the universalism postulated by our own system, in face of which the affirmations of difference that multiply themselves are only reactions), because they were not at all a problem, but the very ground of social logics. I hence avert that such type of general problematic (the multiple scale production of the social by means of the articulation between the differences) is one of the most crucial questions to the historian – independently from the object which one analyses. I shall therefore continue the reflections that I have been undertaking, along with some colleagues, about the matters of the statute, the object and the future of the historical discipline as an attempt to redefine its relative role before the other social sciences, aiming at a reunified science of the social. It is precisely at this point that the matter of difference is able to furnish an interesting key, because for me (and for some others), change is not a condition of the historian’s work, but it's very object. Thus History does not only consist of identifying, by comparison, the differences as signs of a change that would constitute the board of explanation in History (replying to the question of why and how practices have changed), yet of turning difference into its own object, both in space and time, as an empirical form of social dynamics (thus answering the question about how society – in this case, medieval society – produced difference in space and time). That is why I can easily consider that History is the science of change (obviously the social change). Stating that History is the science of (social) change implies that the historian’s object is the historicity of social systems, that is, ineluctably the historicity of social domination systems. By “historicity” I mean both a process of historical formation and transformation of dominium relationships, and the fact that all of them have or will come to an end. The exam of the matter of producing local singularity in Middle Ages allows us to take into account the fact that peoples identified as specific ethnic groups (still during the Carolingian period) have eventually disappeared as to give rise to populations rooted in some location and identified to it (place, region, kingdom) – the concept of "population" having to be understood here in the sense of Michel Foucault. [ABSTRACT FROM AUTHOR]