In contrast to the Neo-Arian belief that the Son is "anomoios", or "unlike" the Father, and with the Semi-Arian assertion that the Son is "homoiousios", or "like" the Father, Gregory and his fellow Cappadocians maintained the Nicaean doctrine of "homoousia", or consubstantiality of the Son with the Father. The Cappadocian Fathers asserted that God's nature is unknowable to man; helped to develop the framework of "hypostases", or three persons united in a single Godhead; illustrated how Jesus is the eikon of the Father; and explained the concept of "theosis", the belief that all Christians can be assimilated with God in "imitation of the incarnate Son as the divine model."