CONSUBSTANTIAL. - It 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 Creed of that council to express the substantial or essential identity of the Son with the Father (ὁμοούσιος τῷ Πατρὶ) and thus to condemn the Arian error, which maintained a diversity of substance or essence (ἐκ ἐτέρας ὑποστάσεως ἢ οὐσίας) between the first two Persons of the Trinity.
But the term ὁμοούσιος, which is found for the first time in the Gnostic literature of the 2nd century and then passes in the 3rd century into Catholic vocabulary, has a history which, through its various vicissitudes, has in recent times stirred up a controversy between Catholics and non-Catholics over the interpretation of the Nicene definition. The Lutheran Th. Zahn, then the liberal Protestants Harnack, Loofs, Seeberg, Gwatkin and finally the false Coulange (Turmel, a priest condemned by the Church) maintained that the term, already rejected in the Synod of Antioch (269), which condemned Paul of Samosata, was adopted by the Nicene Council 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 the 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" (Jo. 10, 30). The term ὁμοούσιος used in this sense is already met with in Origen (In Mt.: PG, 17, 309 A) and is known at Rome under Pope Dionysius (259-68). But since in that era the distinction between οὐσία and ὑπόστασις was not yet clear, the term ὁμοούσιος lent itself to equivocation, because it could mean identity of essence or of person. The Antiochene Synod of 269 condemned the ὁμοούσιος because Paul of Samosata interpreted it in the sense of identity of persons in favor of his modalism (v.). Thus Hilary attests (De Synodis, 81: PL, 10, 534).
At the Nicene Council the term ὁμοούσιος retained its earlier meaning, confirmed also by the Cappadocian Fathers: it formally indicated neither numerical unity nor 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. Virtually, however, the so-called numerical unity was also affirmed, because in the opening of the same Creed of Nicaea it had been defined that there is "one God the Father." After the Council, however, the Arians attacked the ὁμοούσιος as a modalist expression proper to Sabellianism (v.), which removed every 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 looking favorably upon the formula of the Homoiousians (v.), in which not identity but substantial likeness was asserted. Nevertheless these Fathers understood and explained such likeness in an absolute sense, which was equivalent to identity. In short, they unified the use of the technical term without compromising its doctrinal meaning already defined at Nicaea.
Subsequently, once the distinction between οὐσία and ὑπόστασις was clarified, the Latin formula una natura in tribus personis spread also in the East, dispelling every equivocation: μία οὐσία, τρεῖς ὑποστάσεις.
It therefore makes no sense to speak of Neo-Nicenism. In the Council of Constantinople (381) the ὁμοούσιος was claimed also for the Holy Spirit against the Macedonians.