Homoousios

Homoousios is a Greek term meaning “of the same substance” or “of one being.” In Christian theology it denotes the relationship between the Father and the Son, asserting that the Son is not a created being but shares the same divine essence as the Father. The related term homoiousios means “of similar substance,” and was used by some opponents of the Nicene position in early debates.

The term arose in the context of the first major Christological controversy of the 4th century, sparked by Arianism, which claimed that the Son was a subordinate, created entity. The First Council of Nicaea in 325 condemned Arianism and adopted the term homoousios in the Nicene Creed to affirm the Son’s full divinity and equality with the Father. The doctrine was defended by bishops such as Athanasius and later elaborated by the Cappadocian Fathers, who clarified distinctions between essence (ousia) and persons (hypostases) within the Trinity. The Council of Constantinople in 381 reaffirmed and expanded the Nicene framework, stressing the unity of the divine essence across the Father, the Son, and the Holy Spirit.

In Latin-speaking Christian traditions the doctrine is often rendered as consubstantialis. Homoousios remains a cornerstone of mainstream Trinitarian theology in Catholicism, Eastern Orthodoxy, and most forms of Protestantism, signaling the coequal and coeternal divinity of the Son with the Father. Some nontrinitarian groups reject the term, while discussions about its philosophical implications continue in contemporary theology.