On another level, the Chalcedonian perspective confined the meaning of the term "nature" solely to the essential (or substantial) aspect, completely abandoning the specialized theological meaning of the term. This is in contrast to the contextual usage in the Christology of Saints Cyril and Severus. The repercussions of these new definitions can be clearly seen in the understanding of the Word's incarnation. From this point on, "one nature," if taken in an abstract sense, would mean a single essence - precisely what Eutyches advocated by blending the two essences into one. St. Severus rejects the notion of a single essence and refuses to speak of a union of essences. In his letter to Maron, he writes:
"But those people who, blasphemously, say that Christ is one in two natures, using the term 'nature' instead of the singular designation, saying that God the Word is a nature and the man - from Mary, as they claim - is another nature, have not fallen into such a degree of folly that would lead them to claim they use the term 'natures' instead of the general designation, meaning the same as 'essence'. For if the Holy Trinity is one nature, and all humanity is one nature, then by the same logic and principle, we would be saying something absurd: that the Holy Trinity was incarnate in all humanity, i.e., in the whole human race." (Fr. Mark Aziz, 2026, pg. 121)
"For doth he say that the Word out of God is possessor of Godhead, even though any should wish to conceive of Him apart and without flesh? Doth he define His Godhead as other than He, whereof I know not how (as he saith) He hath become possessor, as though it accrued to Him and came to Him from without, although once not God by Nature... Would not one earn laughter and accusation of insanity, if one chose to say that any among us were the possessor of human nature (Η οὐκ ἂν ἔφλοι γέλωτα καὶ φρενοβλαβείας γραφήν, εἰ δὴ βούλοιτό τις ἕνα τῶν καθ ´ ἡμᾶς ἀνθρωπότητος κτήτορα λέγειν, ἤγουν τὸν ἵππον ἱππότητος), or a horse of horse-nature? Who then is the possessor of Godhead, who, taken from men, is ordained in things to God-ward (Heb. v.1)? Haply he will say, severing into two the One Christ, Him that is forth of the Holy Virgin; for to this I suppose now too is his aim directed."
- St. Cyril of Alexandria, 5 Tomes Against Nestorius, Tome 3
According to the Fathers there is no instance of someone applying two universals to one individuation. Essence cannot be one or two in relation to a composite hypostasis.