Homoousion

Homoousion is a Greek theological term meaning “of the same substance.” The First Council of Nicaea used it to affirm that the Son shares the Father’s divine being.

First Council of Nicaea: The 325 council that addressed the Arian controversy and formulated an early creed affirming the Son’s relation to the Father. The council adopted homoousion to state that the Son is of the same substance as the Father.
Trinity: The Christian doctrine that God is one being in three persons: Father, Son, and Holy Spirit. Homoousion addresses how the Son shares the one divine being while remaining distinct from the Father.
Substance: The underlying reality or essence that makes something what it is, especially in philosophical and theological usage. Homoousion applies this concept to the relation between the Father and the Son.
Homoianism: A fourth-century theological position that described the Son as like the Father without specifying sameness or similarity of substance. Its deliberately less precise language avoided homoousion’s claim about the Son’s substance.
Nicene Creed: A Christian creed first formulated at Nicaea in 325 and expanded at Constantinople in 381. Its 325 form used homoousion to express the Son’s unity of substance with the Father.
Nicene Christianity: Christian traditions that confess the central theological claims expressed in the Nicene Creed. Confessing homoousion became a marker of the Nicene account of the Son’s full divinity.
Niceno-Constantinopolitan Creed: The creed associated with the Council of Constantinople in 381, now commonly recited in many Christian traditions. Its wording retains the claim that the Son is of one substance with the Father.
Anomoeanism: A fourth-century theological position holding that the Son is unlike the Father in substance. It opposed the shared divine substance asserted by homoousion more directly than Homoian formulas did.
Arian controversy: A fourth-century Christian dispute over whether the Son is eternal and fully divine or subordinate to the Father. The controversy made the Son’s relation to the Father the question homoousion was meant to answer.
Arianism: A fourth-century theological position associated with Arius that held the Son to be subordinate to the Father and not coeternal. Arian teaching rejected the equality of divine being that homoousion affirms.

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