This article examines the work of the Turkish historian Mehmet Fuad Koprulu on Turkish/Anatolian Islam, which he referred to as 'popular' or 'heterodox'. On the one hand committed to Western scientific standards, on the other part of the project of Turkish nationalism, Koprulu produced an extensive scholarly work that is until today widely accepted as authoritative in the field. Here, my focus is on the concepts Koprulu used in establishing a narrative about the continuity of Turkish culture from pre-Islamic to modern times. His conceptualization of non-elite Muslim currents, which was inspired by both modernist Western discourses on religion and discourses of Islamic apologetics and revivalism, is problematic both because of the normative ambivalences which stem from the conflation of these different discourses and the respective politics in which they are involved. The article develops a critique of concepts in the description of inner-Islamic plurality, and offers suggestions toward approaches that transcend Islamic and modernist biases in terms of origins, essences, and boundaries in cultural and religious traditions.