  Early scholars of Albo’s work in the late nineteenth and early twentieth centuries argued that Albo’s contribution to the history of Jewish thought was limited to his theory of principles and the first treatise of his book (Schlesinger 1844, xi–xiv; Back 1869, 3–5, 8–9; Tänzer 1896, 23–30). Later scholars called his theory unoriginal, and identified the philosophical sources that influenced it, especially Maimonides, Ibn Rushd, Nissim of Gerona, Hasdai Crescas and Simeon ben Zemah Duran (Guttmann 1955, 170–176; Waxman 1956, 158–161; Schweid 1963; Klein-Braslavi 1980, 194–197). A subsequent, third scholarly trend attempted to clarify the nature of the internal relationship between the categories of Albo’s theory of principles (principles, roots, and branches), and examined Albo’s position regarding the concept of heresy (Kellner 1986, 140–156).