The Sethians were one of the main currents of Gnosticism during the 2nd and 3rd century CE, along with Valentinianism and Basilideanism. According to John D. Turner, it originated in the 2nd century CE as a fusion of two distinct Hellenistic Judaic philosophies and was influenced by Christianity and Middle Platonism. However, the exact origin of Sethianism is not properly understood.
The Sethians (Latin Sethoitae) are first mentioned, alongside the Ophites, in the 2nd century, by Irenaeus (who was antagonistic towards gnosticism) and in Pseudo-Tertullian (Ch. 30). According to Frederik Wisse, all subsequent accounts appear to be largely dependent on Irenaeus. Hippolytus repeats information from Irenaeus.
According to Epiphanius of Salamis (c. 375), Sethians were in his time found only in Egypt and Palestine, but fifty years earlier, they had been found as far away as Greater Armenia.
Philaster's (4th century CE) Catalogue of Heresies places the Ophites, Cainites, and Sethians as pre-Christian Jewish sects. However, since Sethians identified Seth with Christ (Second Logos of the Great Seth), Philaster's belief that the Sethians had pre-Christian origins, other than in syncretic absorption of Jewish and Greek pre-Christian sources, has not found acceptance in later scholarship.
Hans-Martin Schenke was one of the first scholars to categorize several texts in the Nag Hammadi library as Sethian.
According to John D. Turner, British and French scholarship tends to see Sethianism as "a form of heterodox Christian speculation," while German and American scholarship views it as "a distinctly inner-Jewish, albeit syncretistic and heterodox, phenomenon." Roelof van den Broek notes that "Sethianism" may never have been a separate religious movement but that the term rather refers to a set of mythological themes that occur in various texts. According to Turner, Sethianism was influenced by Christianity and Middle Platonism, and six phases can be discerned in the interaction of Sethianism with Christianity and Platonism.
Phase 1.