Ethno-history narrative which is designed in accordance with political and social needs rather than historical facts, is also seen in Turkish historiography. The allegation which is secular public law is separate from Islamic law in Turkish states, led by Fuad Koprulu and continued by his students Omer Lutfi Barkan and Halil Inalcik is expressed as a sample of this ethno-history attitude. According to this ethno-history thesis, which aims to provide the historical legitimacy to the new Turkish nation-state based on a secular political system, there has been a secular-political custom law in the Turkish states without the influence of religious law. Even if this paradigm based on Durkheimian theory of social division of labour by Koprulu, in fact, it was created by ignoring the most important assumption of this theoretical perspective. The study will argue the fact that Koprulu, Barkan and Inalcik made this possible by making an artificial distinction between the spheres of religion and politics in Turkish history.