Abstract This article offers a reconsideration of Eriugena’s doctrine of deification (θέωσις | deificatio ) and his Christology in Periphyseon V. It questions the consensus view that Eriugena’s doctrine is fundamentally “Maximian” in character. Some have already critiqued this consensus view, arguing that Eriugena’s Christology and soteriology were shaped more by a heterodox Neoplatonism than by any Christian source(s). The study of Periphyseon V offered here supports a different conclusion. Eriugena’s departure from Maximus arises not from any heterodox or Platonic excess, but from his fidelity to a different Patristic inheritance: a pre‐Maximian, fourth‐century “neo‐Nicene” theological orthodoxy. Particular attention is given to Eriugena’s dependence on Ambrose’s concept of “unification” ( adunatio ) and on Hilary’s account of Christ’s deification. The neglected opinions of these two Latin fathers wrought a decisive influence on Eriugena’s speculative theology which serves, in part, to explain Eriugena’s departure from Maximus.