CONSUBSTANTIAL. — This is the translation of the Greek term ὁμοούσιος (= of the same essence), which became the watchword of orthodoxy against Arianism (v.) at the time of the Council of Nicaea (325) and was inserted into the Symbol of that council to express the substantial or essential identity of the Son with the Father (ὁμοούσιος τῷ Πατρὶ) and thus condemn the Arian error, which maintained a difference of substance or essence (ἐκ ἐτέρας ὑποστάσεως ἡ οὐσίας) between the first two Persons of the Trinity.
However, the term ὁμοούσιος, which first appears in Gnostic literature of the 2nd century and then passes into Catholic usage in the 3rd century, has a history whose various developments have in recent times given rise to a controversy among Catholics and non-Catholics regarding the interpretation of the Nicene definition. The Lutheran Th. Zahn, followed by the liberal Protestants Harnack, Loofs, Seeberg, Gwatkin, and finally the pseudo-Coulange (Turmel, a priest condemned by the Church), argued that the term, already rejected at the Synod of Antioch (269), which condemned Paul of Samosata, was adopted by the Council of Nicaea in the sense of numerical unity, whereas later, especially by the Cappadocian Fathers, it was interpreted in the sense of purely specific unity.
First of all, it must be noted that the concept of essential or substantial unity between the Father and the Son is already found in the Gospel where Christ says: “I and the Father are one” (Jn 10:30). The term ὁμοούσιος used in this sense is already found in Origen (In Mt.: PG, 17, 309 A) and was known in Rome under Pope Dionysius (259–68). But since at that time the distinction between οὐσίας and ὑποστάσεις was not yet clear, the term ὁμοούσιος was open to misunderstanding, as it could mean either identity of essence or identity of person. The Synod of Antioch in 269 condemned ὁμοούσιος because Paul of Samosata interpreted it in the sense of identity of persons in favor of his modalism (v.). So Hilary attests (De Synodis, 81: PL, 10, 534).
At the Council of Nicaea the term ὁμοούσιος retained its previous meaning, confirmed also by the Cappadocian Fathers: it did not formally indicate either numerical unity or purely specific unity. It intended to affirm that the substance of the Word did not belong to the category of creatures but to the same category as that of the Father. In practice, however, it also affirmed the so-called numerical unity, because at the beginning of the very Symbol of Nicaea it had been defined that there is “one God the Father.” After the Council, however, the Arians attacked ὁμοούσιος as a modalist expression proper to Sabellianism (v.), which removed all distinction of person in the Trinity. For this reason the Fathers (Athanasius, Basil) did not insist further on the term but continued to defend the concept of consubstantiality, even making good use of the formula of the Homoiousians (v.), in which they asserted not identity but substantial similarity. Nevertheless, these Fathers understood and explained such similarity in an absolute sense, which is equivalent to identity. In short, they mitigated the use of the technical term without compromising the doctrinal meaning already defined at Nicaea.
Later, when the distinction between οὐσίας and ὑποστάσεις became clear, the Latin formula una natura in tribus personis spread even in the East, dissipating every misunderstanding: μία οὐσία, τρεῖς ὑποστάσεις.
It is therefore meaningless to speak of non-concisionism. At the Council of Constantinople (381) ὁμοούσιος was vindicated also for the Holy Spirit against the Macedonians.