Those of the medieval Cathars, Bogomils, and Carpocratians seem to include elements of both categories. Gilles Quispel divided Syrian-Egyptian Gnosticism further into Jewish Gnosticism (the "Apocryphon of John") and Christian Gnosis (Marcion, Basilides, Valentinus). This "Christian Gnosticism" was Christocentric, and influenced by Christian writings such as the Gospel of John and the Pauline epistles. Other authors speak rather of "Gnostic Christians", noting that Gnostics were a prominent substream in the early church. The best known example of this approach is Adolf von Harnack (1851–1930), who stated that "Gnosticism is the acute Hellenization of Christianity." According to Dillon, "many scholars today continue in the vein of Harnack in reading gnosticism as a late and contaminated version of Christianity", notably Darrell Block, who criticises Elaine Pagels for her view that early Christianity was wildly diverse. Hans Jonas (1903–1993) took an existential phenomenological approach to Gnosticism. According to Jonas, alienation is a distinguishing characteristics of Gnosticism, making it different from contemporary religions. Jonas compares this alienation with the existentialist notion of "geworfenheit", Martin Heidegger's "thrownness," as in being thrown into a hostile world. In the late 1980s scholars voiced concerns about the broadness of "Gnosticism" as a meaningful category. Bentley Layton proposed to categorize Gnosticism by delineating which groups were marked as gnostic in ancient texts. According to Layton, this term was mainly applied by heresiologists to the myth described in the "Apocryphon of John", and was used mainly by the Sethians and the Ophites. According to Layton, texts which refer to this myth can be called "classical Gnostic". In addition, Alastair Logan uses social theory to identify Gnosticism. He uses Rodney Stark and William Bainbridge's sociological theory on traditional religion, sects and cults. According to Logan, the Gnostics were a cult, at odds with the society at large. According to Michael Allen Williams, the concept of Gnosticism as a distinct religious tradition is questionable, since "gnosoi" was a pervasive characteristics of many religious traditions in antiquity, and not restricted to the so-called Gnostic systems. According to Williams, the conceptual foundations on which the category of Gnosticism rests are the remains of the agenda of the heresiologists.