Different versions of the same dataset show that concepts change their meaning over time, especially if the time gap is wide. Although not meaning exactly the same, two time gapped instances of the same concept may preserve some degree of sameness. For example, the concept shoemaker in the 17th century (someone who makes shoes with leather) has drifted until nowadays (someone who owns a company). Mapping drifted concepts correctly is necessary to solve longitudinal queries in Humanities data. [...] We will study what precise relationship holds between two different versions of a changing concept, identifying the presence of a drift and its nature. Using Description Logics work on ontology diff [3], we will define a minimum meaning concept core, which keeps stable over time despite other non essential transformations. A data model to represent drifted concepts will be needed. A systematic comparison between unstable concept properties will tell whether a drift occurred, and its type.