Question: "What is monophysitism? What is Eutychianism?"
Answer: Monophysitism is an erroneous or heretical view concerning the nature of Jesus Christ. Two monophysite schools of thought are Eutychianism and Apollinarianism. Monophysitism taught that Christ has one nature—a divine one—not two. Eutychianism specifically taught that Christ’s divine nature was so intermixed with His human nature that He was, in fact, not fully human and not fully divine. Eutychianism and monophysitism are a denial of the biblical teaching of the hypostatic union, that Christ’s two natures are united yet distinct. Eutychians followed the teaching of Eutyches (378–452), a fifth-century leader of a monastery in Constantinople; the word monophysitism comes from a Greek word meaning “one nature.”
Eutychianism developed as a fifth-century response to Nestorianism, which taught that Christ has two separate natures resulting in two different persons residing in the same body. Eutyches, however, went too far in his refutation of Nestorius and ended up teaching heresy as well. Eutyches said that Jesus’ humanity was essentially dissolved or obliterated by His divine nature, describing it as being “dissolved like a drop of honey in the sea.” An analogy that might help explain what Eutyches meant is a drop of ink put into a glass of water. The result is a mixture that is not pure water or pure ink. Instead, it is a third substance, a mixture of the two in which both the ink and water are changed in some way. In essence, that is what Eutyches taught about the natures of Christ. He believed that the human nature of Christ was absorbed into His divine nature in a way that both natures were changed to some degree, which resulted in a third nature being formed.
Monophysitism, including Eutychianism, was more influential in the Eastern Church than in the West. The teaching was renounced at the Council of Chalcedon in AD 451, but, at one point in the late fifth century, the Patriarch of the Eastern Orthodox Church sought to reconcile monophysitism with orthodox teaching. No agreement could be reached, and the monophysites were eventually excommunicated. Monophysitism continued to be widely accepted, however, in Syrian Antioch, Jerusalem, and Alexandria, Egypt.
Later, some people put forward a compromise between monophysitism and orthodox theology called monothelitism (from a Greek word for “one will”). Promoters of monothelitism said that Christ had two natures yet only had one (divine) will. This denial of Jesus’ human will ignored Jesus’ own statement in Luke 22:42, and the compromise failed, being rejected by both sides. Monophysites refused to accept the doctrine of Christ’s two natures, and monothelitism was itself declared heresy by the Third Council of Constantinople (680–681).
Some churches today teach what can be considered a modified form of monophysitism called miaphysitism or henophysitism. Miaphysitism teaches that Christ has one nature, but that one nature consists of two natures, united in one “without mingling, without confusion, and without alteration” (from the Coptic divine liturgy). Oriental Orthodox churches, including the Coptic Orthodox Church, hold to miaphysite or non-Chalcedonian doctrine.
The shared error of monophysitism and Eutychianism is the teaching that Christ had only one nature. The doctrine of Christ’s nature is critical when it comes to the atonement. Had Jesus not been truly and fully man, then He could not have been a true substitute for humanity; had He not been truly and fully God, then His death could not have atoned for our sins.