In order to preserve the unity of Christ's personality, some felt it necessary to reject the doctrine of two natures. This led in several directions:
Docetism teaches that Jesus' physical body was an illusion, as was his crucifixion; that is, Jesus only seemed to have a physical body and to physically die, but in reality he was incorporeal, a pure spirit, and hence could not physically die. This belief treats John 1:14 ("The Word was made flesh and dwelt among us") as merely figurative. Docetism is regarded as heretical by the Catholic Church, Orthodox Church, and many others.
Apollinarism or Apollinarianism was a view proposed by Apollinaris of Laodicea (died 390) that Jesus could not have had a human mind; rather, that Jesus had a human body and lower soul (the seat of the emotions) but a divine mind. It was declared to be a heresy in 381 by the First Council of Constantinople. Followers of Apollinarianism were accused of attempting to create a tertium quid ("third thing," neither God nor man).