A theological term succinctly expressing the definition of the Council of Chalcedon (451) concerning the Incarnation: that in Christ the two natures, each retaining its own properties, are united in one Person; not, therefore, two persons morally or accidentally united (according to Nestorius), nor two natures commingled (Eutyches), but two perfect natures united hypostatically, i.e.,in the one Person of the Word, who is thus both perfect God and perfect man.