Gnosticism, dualistic religious and philosophical movement of the late Hellenistic and early Christian eras. The term designates a wide assortment of sects, numerous by the 2d cent. A.D.; they all promised salvation through an occult knowledge that they claimed was revealed to them alone. Scholars trace these salvation religions back to such diverse sources as Jewish mysticism, Hellenistic mystery cults, Iranian religious dualism (see Zoroastrianism), and Babylonian and Egyptian mythology. The definition of gnosis [knowledge] as concern with the Eternal was already present in earlier Greek philosophy, although its connection with the later Gnostic movement is distant at best. Christian ideas were quickly incorporated into these syncretistic systems, and by the 2d cent. the largest of them, organized by Valentinus and Basilides, were a significant rival to Christianity. Much of early Christian doctrine was formulated in reaction to this movement.

Until the discovery at Nag Hammadi in Egypt of key Manichaean (1930) and Coptic Gnostic (c.1945) papyri, knowledge of Gnosticism depended on Christian sources, notably St. Irenaeus, St. Hippolytus, Tertullian, and Clement of Alexandria. Among principal Gnostic writings are the Valentinian documents Pistis-Sophia and the Gospel of Truth (perhaps by Valentinus himself). Important too is the literature of the Mandaeans in modern Iraq, who are the only Gnostic sect extant. Gnostic elements are found in the Acts of Thomas, the Odes of Solomon, and other wisdom literature of the pseudepigrapha.

Some Gnostics taught that the world is ruled by evil archons, among them the deity of the Old Testament, who hold captive the spirit of humanity. The heavenly pleroma was the center of the divine life, and Jesus was interpreted as an intermediary eternal being, or aeon, sent from the pleroma to restore the lost knowledge of humanity's divine origin. Gnostics held secret formulas, which they believed would free them at death from the evil archons and restore them to their heavenly abode. See Valentinus for typical Gnostic teaching on the pleroma.

Gnosticism held that human beings consist of flesh, soul, and spirit (the divine spark), and that humanity is divided into classes representing each of these elements. The purely corporeal (hylic) lacked spirit and could never be saved; the Gnostics proper (pneumatic) bore knowingly the divine spark and their salvation was certain; and those, like the Christians, who stood in between (psychic), might attain a lesser salvation through faith. Such a doctrine may have inspired extreme asceticism (as in the Valentinian school) or extreme licentiousness (as in the sect of Caprocrates and the Ophites). The influence of Gnosticism on the later development of the Jewish kabbalah and heterodox Islamic sects such as the Ismailis is much debated.

Religious and philosophical movement popular in the Roman world in the 2nd–3rd century AD. The term, based on the Greek gnōsis (“secret knowledge”), was coined in the 17th century, when it was applied liberally to ancient Christian heretical sects, especially those described by their orthodox contemporaries as radically dualistic and world-denying, and those who sought salvation through esoteric revelation and mystical spirituality. In the late 19th and the early 20th century, that view of Gnosticism was replaced with several groupings, and the discovery of the Nag Hammadi texts in 1945 greatly enhanced the understanding of Gnosticism. The relationship with ancient Christianity remains uncertain, but the Gospel of Thomas and the Gospel of Mary (which portrays Mary Magdalene as a leading apostle) are generally seen as being grounded in Gnosticism. They emphasized the teachings of Jesus, rather than his death and resurrection, as the key to salvation. The teachings of Valentinus were the basis of the Gospel of Truth, a fusion of Christian and Gnostic beliefs. Other texts previously considered Gnostic are now assigned to distinct religious traditions, especially Hermeticism (see Hermetic writings), Mandaeanism, and Manichaeism. The texts of the Sethians have the best claim to the designation “Gnostic”; they describe one supreme, good God and the creation, by a junior heavenly being (Sophia), of an arrogant creature who then claims to be God. That creature withholds from humanity moral knowledge and eternal life, but Sophia plants the divine spirit within people to save them. Male and female saviours (including Jesus) were sent from the world above to instruct humanity in the knowledge of the true God and humanity's own divine nature. In general, Gnostics taught cosmological dualism, strict asceticism, repudiation of material creation as evil, docetism, and the existence of the divine spark in humans.

Learn more about Gnosticism with a free trial on Britannica.com.