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 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 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 on his death on the cross.
Christology and theological implications
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 of 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 "He 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.
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, while a distinct minority holds that he is concerned with a group that commingled Judaism and docetism. Other possibilities are that he was merely opposed to Christians who lived Jewishly, or deny that docetism threatened the church, or that his critical remarks were directed at an Ebionite or Cerinthian possessionist Christology, where God descended and took possession of Jesus' body. 
Islam and docetism
The Qur'an has a docetic or gnostic 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.
Docetism and Christ myth theory
Since Arthur Drews published his The Christ Myth (Die Christusmythe) in 1909, occasional connections have been drawn between the modern idea that Christ was a myth and docetist theories. 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".
Texts believed to include docetism
Non-canonical Christian texts
- 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
- Christian heresy
- Eidolon (apparition)
- Islamic view of Jesus' death
- González 2005, pp. 46–47:"A term derived from the Greek dokein, to seem, or to appear."
- Strecker 2000, p. 438.
- Brox 1984, p. 306.
- Schneemelcher Maurer, p. 220.
- Breidenbaugh 2008, pp. 179–181
- Ehrman 2005, p. 16.
- Foster 2009, p. 79. Serapion first approved its use, and only reversed his opinion on returning to his bishopric in Antioch, after being informed of its contents. He wrote a "Concerning the So-Called Gospel of St Peter" which is alluded to in Eusebius of Caesarea's Historia Ecclesiastica VI 12.3–6.
- Smith & Wace 1877, pp. 867–870.
- Ridgeon 2001, p. xv.
- Arendzen 2012.
- Gonzalez, Justo (2005). Essential Theologial Terms. Louisville: Westminster John Knox Press. pp. 46–47. ISBN 0-664-22810-0. "Docetism is the claim that Jesus did no thave a physical human body, but only the appearance of such."
- Brox 1984, pp. 301–314.
- Schneemelcher Maurer, p. 220:"N Brox has expressed himself emphatically against a widespread nebulous use of the term, and has sought an exact definition which links up with the original usage (e.g. in Clement of Alexandria). Docetism is ‘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.'
- Price 2009.
- Ehrman 2005, p. 16
- Ehrman 1996, p. 197.
- Larsen 2008, p. 347
- Gavrilyuk 2004, p. 80.
- Schneemelcher Maurer, p. 220
- Brox 1984, p. 314.
- González 2005, pp. 46–7
- Ashwin-Siejkowski 2010, p. 95, n.2 citing Edwards 2002, p. 25.
- Street 2011, p. 40.
- Streett 2011, pp. 42–43.
- Pickthall 2001, p. 86
- Shailer 1917, p. 37.
- Conybeare 1914, p. 104.
- Grant 2004, pp. 199–200:"This skeptical way of thinking reached its culmination in the argument that Jesus as a human being never existed at all and is a myth. In ancient times, this extreme view was named the heresy of docetism (seeming) because it maintained that Jesus never came into the world "in the flesh", but only seemed to; (I John 4:2) and it was given some encouragement by Paul's lack of interest in his fleshly existence. Subsequently, from the eighteenth century onwards, there have been attempts to insist that Jesus did not even "seem" to exist, and that all tales of his appearance upon the earth were pure fiction. In particular, his story was compared to the pagan mythologies inventing fictitious dying and rising gods."
- Arendzen, J. (2012) . "Docetae". The Catholic Encyclopedia 5. Robert Appleton Company. Retrieved 25 April 2012.
- Ashwin-Siejkowski, Piotr (2010). "The Docetic View of Christ". Clement of Alexandria on Trial: The Evidence of "Heresy" from Photius' Bibliotheca. Vigiliae Christianae 101. Brill. pp. 95–113. ISBN 978-0-19-518249-1. Retrieved 25 April 2012.
- Breidenbaugh, Joel R. (2008). "Docetism". In Hindson, Ed; Caner, Ergun; Verstraete, Edward J. The Popular Encyclopedia of Apologetics: Surveying the Evidence for the Truth of Christianity. Harvest House Publishers. pp. 186–193. ISBN 978-0-7369-2084-1. Retrieved 25 April 2012.
- Brox, Norbert (1984). "'Doketismus' – eine Problemanzeige". "Zeitschrift für Kirchengeschichte" 95. Kohlhammer Verlag. pp. 301–314. ISSN 0044-2925.
- Conybeare, Frederick Cornwallis (1914). The Historical Christ: Or, An Investigation of the Views of Mr. J. M. Robertson, Dr. A. Drews, and Prof. W. B.. Open court Publishing Company. Retrieved 25 April 2012.
- Edwards, Mark J. (2002). Origen against Plato. Ashgate Studies in Philosophy & Theology in Late Antiquity. Ashgate. ISBN 978-0-7546-0828-8. Retrieved 25 April 2012.
- Ehrman, Bart D. (1996). The Orthodox Corruption of Scripture: The Effect of Early Christological Controversies on the Text of the New Testament. Oxford University Press. ISBN 978-0-19-974628-6. Retrieved 25 April 2012.
- Ehrman, Bart D. (2005). Lost Christianities: The Battles for Scripture and The Faiths We Never Knew (2 ed.). Oxford University Press. ISBN 978-0-19-518249-1. Retrieved 25 April 2012.
- Foster, Paul (2009). The Apocryphal Gospels: A Very Short Introduction. Very Short Introductions 201. Oxford University Press. ISBN 978-0-19-923694-7. Retrieved 25 April 2012.
- Gavrilyuk, Paul L. (2004). The Suffering of the Impassible God: The Dialectics of Patristic Thought. Oxford Early Christian Studies. Oxford University Press. ISBN 978-0-19-926982-2. Retrieved 25 April 2012.
- González, Justo L. (2005). Essential Theological Terms. Westminster John Knox Press. ISBN 978-0-664-22810-1. Retrieved 25 April 2012.
- Grant, Michael (2004) . Jesus. Rigel. ISBN 978-1-898799-88-7. Retrieved 25 April 2012.
- Larsen, Kasper Bro (2008). "Narrative Docetism: Christology and Storytelling in the Gospel of John". In Bauckham, Richard; Mosser, Carl. The Gospel of John and Christian Theology. Wm. B. Eerdmans Publishing. pp. 346–355. ISBN 978-0-8028-2717-3. Retrieved 25 April 2012.
- Mathews, Shailer (2006) . The Spiritual Interpretation of History. Cosimo, Inc. ISBN 978-1-59605-138-6. Retrieved 25 April 2012.
- Pickthall, Muhammad M. (2001) . The Glorious Qur'an: The Arabic Text with a Translation in English. TTQ, INC. ISBN 978-1-879402-51-5. Retrieved 25 April 2012.
- Price, Robert (2009). "Review: Timothy Freke and Peter Gandy, Jesus and the Lost Goddess: The Secret Teaching of the Original Christians". Retrieved 25 April 2012.
- Ridgeon, Lloyd V. J. (2001). Ridgeon, Lloyd V. J., ed. Islamic Interpretations of Christianity. Palgrave Macmillan. ISBN 978-0-312-23854-4. Retrieved 25 April 2012.
- Schneemelcher, Wilhelm; Maurer, Christian (1994) . "The Gospel of Peter". In Schneemelcher, Wilhelm; Wilson, McLachlan. New Testament Apocrypha: Gospels and related writings. New Testament Apocrypha 1. Westminster John Knox Press. pp. 216–227. ISBN 978-0-664-22721-0. Retrieved 25 April 2012.
- Smith, William George; Wace, Henry, eds. (1877). A dictionary of Christian biography, literature, sects and doctrines. John Murray. pp. 867–870. Retrieved 25 April 2012.
- Strecker, Georg (2000). Horn, Friedrich Wilhelm, ed. Theology of the New Testament. Walter de Gruyter. ISBN 978-3-11-015652-2. Retrieved 25 April 2012.
- Streett, Daniel R. (2011). They Went Out from Us: The Identity of the Opponents in First John. Beihefte zur Zeitschrift für die neutestamentliche Wissenschaft und die Kunde der älteren Kirche 177. Walter de Gruyter. ISBN 978-3-11-024770-1.
- Docetae in the Catholic Encyclopedia