A fourth-century heresy that denied the divinity of Jesus Christ. Its author was Arius (256-336), a priest of Alexandria, who in 318 began to teach the doctrine that now bears his name. According to Arius there are not three distinct persons in God, co-eternal and equal in all things, but only one person, the Father. The Son is only a creature, made out of nothing, like all other created beings. He may be called God but only by an extension of language, as the first and greatest person chosen to be divine intermediary in the creation and redemption of the world.
In the Arian system, the logos or word of God is not eternal. There was a time when he did not exist. He is not a son be nature, but merely by grace and adoption. God adopted him in prevision of his merits, since he might have sinned but did not. In a word, instead of being God he is a kind of demiurge who advanced in virtue and merit and thus came to be closely associated with the Father. But his nature is not of the same substance as the Father's.
Boldly anti-Trinitarian, Arianism struck at the foundations of Christianity by reducing the Incarnation to a figure of speech. If the logos was created and not divine, God did not become man or redeem the world, and all the consequent mysteries of the faith are dissolved.
The First Council of Nicaea was convoked in 325 to meet the Arian crisis. Since the signature lists are defective, the exact number of prelates who attended the council is not known. However, at least two hundred twenty bishops, mostly from the East but also from Africa, Spain, Gaul, and Italy, signed the creed that affirmed the divinity of Christ and condemned Arius as a heretic. "We believe," the formula read, "in one God, the Father Almighty, Creator of all things visible and invisible. And in one Lord Jesus Christ, the Son of God, the only-begotten of the Father, that is, of the substance of the Father; God from God, light from light, true God from true God; begotten, not created, consubstantial [Greek Homo ousion] with the Father." The soul of the council was St. Athanasius (296-373), Bishop of Alexandria, whose resolute character and theological insight were the main obstacle to the triumph of Arianism in the East.
Since the fifth century, Arian churches have remained in existence in many countries, although some of them were absorbed by Islam. A principal tenet of these churches is the recognition of Christ as Messiah but denial that he is the natural Son of God.