 Since their introduction, Hempel’s model and its weaker versions have been challenged as neither generally applicable not appropriate. The demarcation criterion of unity is undermined by criteria of demarcation between natural and historical sciences. For instance, historical explanations have a genealogical or narrative form, or else they require the historian’s engaging problems or issuing a conceptual judgment that brings together meaningfully a set of historical facts (recent versions of such decades-old arguments are in Cleland 2002, Koster 2009, Wise 2011). According to more radical views, natural sciences such as geology and biology are historical in their contextual, causal and narrative forms; also that Hempel’s model, especially the requirement of empirically testable strict universal laws, is satisfied by neither the physical sciences nor the historical sciences, including archeology and biology (Ereshefsky 1992).