Christianity
In Christianity, dualistic concepts appeared principally in its gnostic developments. But even in the 2nd-century Judaizing sect of the Encratites, which was not really gnostic, there were dualistic aspects that had modified some tendencies of later Judaism. These teachings were also particularly prominent in the writings of the supporters of Docetism (the doctrine that Christ, being divine, did not suffer and die; 2nd century), who held that matter is essentially evil and that the soul is a preexistent substance. According to the Encratites, the preexistent soul, once it “gets effeminated by concupiscence,” drops into the carnal world. Since generation perpetuates the soul’s state of decay in this bodily world, the Encratites condemned all sexual relations.
The dualism of Marcion (a 2nd-century semi-gnostic Christian heretic) was really a ditheism (a system positing two gods), though common gnostic presuppositions—such as antisomatism and anticosmism, the condemnation of the body and the material universe—were also present in his thought. For Marcion, the God of the Hebrew Bible (Old Testament) is an inferior and harsh creator demiurge, author of the world and of humankind, who is nonetheless completely distinct from the supreme divinity, who manifested himself in Jesus and is a stranger to this world.
For Saturninus (or Satornil) of Antioch, the founder of a 2nd-century Syrian gnostic group that was commonly connected with the tradition of Simon Magus (reputed leader of an earlier gnostic sect), the God of the Hebrew Bible is only one of the angels, the martial angel of the Judaic nation, although (as with Marcion) he is distinct from the Devil, who is in fact his opponent. According to Saturninus, a primordial accident caused a wave of pneuma (“spirit”) to land in the inferior darkness, where it is said to have remained prisoner and now continues its existence in those who, characterized by the presence in them of this superior element, will later be conducted back to their heavenly origin by Jesus, a messenger coming from above.
Conceptions of a similar type are also found in the “Psalm [or Hymn] of the Naassenes” (Naassene is the Hebrew term for Ophite, mentioned above) and in the “Song of the Pearl” in the gnostic Acts of Thomas; here also occurs the concept of a “saviour to be saved,” who has been sent from above and was made a prisoner by darkness. This basic concept was developed fully only in Manichaeism.
The gnostic-dualist view survived in late antiquity and into the Middle Ages, both in the East, among the Mandaeans, Yazīdī, and some extreme sects within the Shīʿite branch of Islam, and in the West, among the Bogomils and Cathari. It is still present today in modern theosophy.