Ousia
The single nature or essence the three divine persons share — what God is, as opposed to who. Nicene Christianity says the Son is homoousios with the Father: of one ousia, not a similar or lesser one.
Greek ousia, “being” or “essence”, from einai, “to be”. Homoousios is “of the same ousia”.
Ousia is what is one in God: the essence, the nature, the "what". After Nicaea, to say the Son is *homoousios* with the Father is to say they are not two gods of similar rank, and not a greater and a lesser. They are of one being.
Debby needs the word because almost every Trinity argument in this Library is a claim about how *ousia* and *hypostasis* can both be counted without contradiction. Gregory of Nazianzus's formula, independently verified in OTC-007, splits the work: "each God because consubstantial; one God because of the monarchy." Shared ousia is the ground of each person's divinity; the Father's monarchy is the ground of the Godhead's unity. That is a doctrine, not yet a derivation of why there are three.
The mistaken everyday reading is "essence" as a chemical or a vibe — a stuff you could have more or less of. Divine ousia is not a quantity and not a component. Treating it as a fourth thing alongside the three persons is the error Eastern writers keep warning against, including in popular EO teaching this corpus has already extracted.
Where this comes up
Sources
- First Council of Nicaea (325); Debby research packets OTC-002 and OTC-007