A word with a century-long history in early Christianity before it became celebrated when employed in the Nicene Creed (325) and applied to the Son of to define His relation to the Father ( to patri). In English translations it has usually been rendered “of one substance with,” or “consubstantial,” or “one in being with.” Its use before 325 is obscure, but certain moments in its history stand out. The Gnostics sometimes used it to describe some souls as “consubstantial with the devil”; ORIGEN used it occasionally, but the evidence that he applied it to the Son is doubtful.

of Samosata apparently used it in defending himself against a charge of between 264 and 268, although his use of the word is difficult to determine. A little before this, Dionysius, bishop of Rome, and DIONYSIUS, bishop of Alexandria, came into an amicable in which the former reproached the latter for not accepting homoousios as applied to the Son. The finally accepted the term, though with some reluctance.

The exact of homoousion in the has been much debated. The theory was widely accepted by Harnack and by Loofs that the main influence must have been that of Ossius, bishop of Cordoba, who was president of the Council of NICAEA and whose theological tradition, like that of virtually all Western theologians of the time, stemmed from Tertullian. Tertullian had declared that the Son was “of one substance” (unius substantiae) or “of the same substance” (eiusdem substantiae) with the Father, and at first sight this seems to settle the problem.

But study of the subject by C. Stead has seen reason to revise this judgment. In the first place, Tertullian’s consubstantiality is in fact very different from fourth-century concepts of the word, being based on a conception of as a substance. In the second place, it has been shown that the term was used in a much less precise way than had been thought, and it is a word of Greek, not of Latin, origin. Its very imprecision, according to E. Schwartz, was its value for Emperor I, who dominated the council. Others have thought that the chief reason for its inclusion was that in his Thaleia, ARIUS had rejected it, and it would therefore serve as a specific point of against ARIANISM.

Shortly after 325 the word drops out of the controversy, even in the writings of ATHANASIUS. But Athanasius, after his decisive break with Emperor Constantius (356), returns to it; and the chief object of his struggle thereafter becomes the attempt, ultimately successful, to persuade all opponents of Arianism to adopt it as their watchword. The Western pro-Nicenes—Hilary, Marius Victorinus, Lucifer, and the others—steadily championed it against Arianism and also, when necessary, against the alternative homoiousion (“of similar substance”) beloved of some Eastern anti-Arians, especially Basil of Ancyra. Between 368 and 380 the great Cappadocian theologians defended and expounded homoousion as predicated both of the Son and of the Spirit, with the result that the term was incorporated—applied to the Son, though not to the Spirit—in the Creed of Constantinople (381) to denote identity of Being without contradicting distinction of Persons.


  • Bethune-Baker, J. F. The of Homoousios in the Constantinopolitan Creed. Texts and Studies 7. Cambridge, 1901.
  • Hanson, R. P. C. The Search for the Christian of God. Edinburgh, 1988.
  • Harnack, A. History of Dogma, Vol. 4, p. 56. New York, 1958.
  • Kraft, H. “Homoousios.” Zeitschrift für Kirchengeschichte 66 (1954-1955):1-24.
  • Loofs, F. “Das Nicänum.” In Festgabe für K. Müller, ed. O. Scheel. Tübingen, 1922.
  • Schwartz, E. Constantin und die christliche Kirche. Berlin, 1913.
  • Stead, C. Divine Substance. Oxford, 1977.