In Christian terminology, docetism (from the Greek δοκεῖν/δόκησις dokeĩn (to seem) dókēsis (apparition, phantom), according to Norbert Brox, is defined narrowly as "the doctrine according to which the phenomenon of Christ, his historical and bodily existence, and thus above all the human form of Jesus, was altogether mere semblance without any true reality." Broadly it is taken as the belief that Jesus only seemed to be human, and that his human form was an illusion. The word Δοκηταί Dokētaí (illusionists) referring to early groups who denied Jesus' humanity, first occurred in a letter by Bishop Serapion of Antioch (197–203), who discovered the doctrine in the Gospel of Peter, during a pastoral visit to a Christian community using it in Rhosus, and later condemned it as a forgery. It appears to have arisen over theological contentions concerning the meaning, figurative or literal, of a sentence from the Gospel of John: "the Word was made Flesh".
Docetism was unequivocally rejected at the First Council of Nicaea in 325 and is regarded as heretical by the Catholic Church, Orthodox Church, and Coptic Church.
Docetism is broadly defined as any teaching that claims that Jesus' body was either absent or illusory. The term 'docetic' should be used with caution, since its use is rather nebulous. For Robert Price "docetism", together with "encratism", "Gnosticism" and "adoptionism", has been employed "far beyond what historically descriptive usage would allow". Two varieties were widely known. In one version, as in Marcionism, Christ was so divine that he could not have been human, since God lacked a material body, which therefore could not physically suffer. Jesus only appeared to be a flesh-and-blood man; his body was a phantasm. Other groups who were accused of docetism held that Jesus was a man in the flesh, but Christ was a separate entity who entered Jesus's body in the form of a dove at his baptism, empowered him to perform miracles, and abandoned him upon his death on the cross.
Docetism's origin within Christianity is obscure. Ernst Käsemann controversially defined the Christology of St John’s Gospel as "naïve docetism" in 1968. The ensuing debate reached an impasse as awareness grew that the very term "docetism", like "gnosticism", was difficult to define within the religio-historical framework of the debate. It has occasionally been argued that its origins were in heterodox Judaism or Oriental and Grecian philosophies. The alleged connection with Jewish Christianity would have reflected Jewish Christian concerns with the inviolability of (Jewish) monotheism. Docetic opinions seem to have circulated from very early times, 1 John 4:2 appearing explicitly to reject them. Some 1st century Christian groups developed docetic interpretations partly as a way to make Christian teachings more acceptable to pagan ways of thinking about divinity.
In his critique of the theology of Clement of Alexandria, Photius in his Myriobiblon held that Clement's views reflected a quasi-docetic view of the nature of Christ, writing that "[Clement] hallucinates that the Word was not incarnate but only seems to be." (ὀνειροπολεῖ καὶ μὴ σαρκωθῆναι τὸν λόγον ἀλλὰ δόξαι.) In Clement’s time, some disputes contended over whether Christ assumed the "psychic" flesh of mankind as heirs to Adam, or the "spiritual" flesh of the resurrection. Docetism largely died out during the first millennium AD.
The opponents against whom Ignatius of Antioch inveighs are often taken to be Monophysite docetists. In his letter to the Smyrnaeans, 7:1, written around 110 AD, he writes:
They abstain from the Eucharist and from prayer, because they confess not the Eucharist to be the flesh of our Saviour Jesus Christ, which suffered for our sins, and which the Father, of His goodness, raised up again. They who deny the gift of God are perishing in their disputes.
While these characteristics fit a Monophysite framework, a slight majority of scholars consider that Ignatius was waging a polemic on two distinct fronts, one Jewish, the other docetic; a minority holds that he was concerned with a group that commingled Judaism and docetism. Others, however, doubt that there was actual docetism threatening the churches, arguing that he was merely criticizing Christians who lived Jewishly or that his critical remarks were directed at an Ebionite or Cerinthian possessionist Christology, according to which Christ was a heavenly spirit that temporarily possessed Jesus.
The Qur'an has a docetic Christology, viewing Jesus as a divine illuminator rather than the redeemer (as he is viewed in Christianity). However, the Islamic docetism is not focused on the general life and person of Jesus or the Christ. In Islam "the Christ" (al-masīḥ) is not generally viewed as distinct from humanity nor a special spirit being as in docetism or some gnosticisms. Islamic docetism focuses on a denial of the crucifixion of Jesus. Sura 4:157–158 reads:
And because of their saying: We slew the Messiah, Jesus son of Mary, Allah's messenger — they slew him not nor crucified him, but it appeared so unto them; and lo! those who disagree concerning it are in doubt thereof; they have no knowledge thereof save pursuit of a conjecture; they slew him not for certain. But Allah took him up unto Himself. Allah was ever Mighty, Wise.
Since Arthur Drews published his The Christ Myth (Die Christusmythe) in 1909, occasional connections have been drawn between docetist theories and the modern idea that Christ was a myth. Shailer Mathews called Drews' theory a "modern docetism". Frederick Cornwallis Conybeare thought any connection to be based on a misunderstanding of docetism. The idea recurred in classicist Michael Grant's 1977 review of the evidence for Jesus, who compared modern scepticism about an historical Jesus to the ancient docetic idea that Jesus only seemed to come into the world "in the flesh". Modern theories did away with "seeming".Gospel of Phillip
Second Treatise of the Great Seth
Gnostic Apocalypse of Peter
Gospel of Judas
In the Contra epistulam fundamenti (Against the Fundamental Epistle), Augustine of Hippo makes reference to the Manichaeans believing that Jesus was Docetic.
Gospel of Peter
Acts of John
Gospel of Basilides