The aim of this chapter is to show why medieval vernacular texts should not be edited, as they usually are, on the basis of a single manuscript, in cases where other witnesses allow for a comparative approach. The increasing weakness of Romance philology in the area of the humanities is in part due to its focus on the single manuscript, understood as a guarantee of historical “reality.” Philology has thus often lost sight of the diachronic dimension of medieval textuality, thereby distancing itself from contemporary historiography, itself based on the interpretation of facts rather than on their description. Examples of the Mort Artu demonstrate how such a synchronic approach impedes one from taking into account even the singularity of the manuscript in question. The diachronic vision afforded by a stemma, however, allows for the reconstruction of the textual tradition’s history and for a critical edition that takes it into consideration (limit-case, the Lai de l’ Ombre). Anachronism—inevitable in any philological act—is therefore a value to be tolerated rather than a peril to be avoided.