Consubstantial (Latin: consubstantialis) is an adjective used in Latin Christian christology, coined by Tertullian in Against Hermogenes 44, used to translate the Greek term homoousios. "Consubstantial" describes the relationship among the Divine persons of the Christian Trinity and connotes that God the Father, God the Son, and God the Holy Ghost are "of one substance" in that the Son is "begotten" "before all ages" or "eternally" of the Father's own being, from which the Spirit also eternally "proceeds". In Latin languages it is the term for homoousism.
Since the Latin language lacks a present active participle for the verb "to be", Tertullian and other Latin authors rendered the Greek noun "ousia" (being) as "substantia", and the Greek adjective "homoousios" (of the same being) as "consubstantialis". Unlike the Greek words, which are etymologically related to the Greek verb "to be" and connote one's own personal inherent character, "substantia", connotes matter as much as it connotes being.
The term is also used to describe the common humanity which is shared by all human persons. Thus, Jesus Christ is said to be consubstantial with the Father in his divinity and consubstantial with us in his humanity.
It has also been noted that this Greek term "homoousian" or "consubstantial", which Athanasius of Alexandria favored, and was ratified in the Nicene Council and Creed, was actually a term reported to also be used and favored by the Sabellians in their Christology. And it was a term that many followers of Athanasius were actually uneasy about. The "Semi-Arians", in particular, objected to the word "homoousian". Their objection to this term was that it was considered to be un-Scriptural, suspicious, and "of a Sabellian tendency". This was because Sabellius also considered the Father and the Son to be "one substance". Meaning that, to Sabellius, the Father and Son were "one essential Person". This notion, however, was also rejected at the Council of Nicaea, in favor of the Athanasian formulation and creed, of the Father and Son being distinct yet also co-equal, co-eternal, and con-substantial Persons.
Some English-speaking translators and authors still prefer the words "substance" and "consubstantial" to describe the nature of God in Christianity.
Translations of the Nicene Creed into English often reflect the preference of using "of the same being" rather than "consubstantial" to describe the relationship of the Son to the Father. When the new translation of the Roman Missal was introduced in 2011, "consubstantial" was introduced as the more accurate translation of the text in Latin. It replaced the phrase "one in being" and was attacked as being archaic. The change was defended because "one in being" was considered to be too ambiguous.
"Consubstantiality", in rhetoric, is often associated with Kenneth Burke. It is defined by Burke as "a practice-related concept based on stylistic identifications and symbolic structures, which persuade and produce acceptance: an acting-together within, and defined by, a common context". To be consubstantial with something is to be identified with it, to be associated with it; yet at the same time, to be different from what it is identified with. It can be seen as an extension or in relation to the subject.
Burke explains this concept with two entities, A and B. He goes on to explain that "A is not identical with his colleague, B. But insofar as their interests are joined, A is identified with B. Or he may identify himself with B even when their interests are not joined, if he assumes they are, or is persuaded to believe so...In being identified with B, A is 'substantially one' with a person other than himself. Yet at the same time, he remains unique, an individual locus of motives. Thus he is both joined and separate, at once a distinct substance and consubstantial with another."
The definition mentions "identifications", which is intended to acknowledge a common practice of rhetoricians. This practice specifically labels something to be clear on the intended meaning of the phrase in the context in which it is being used. Identifying the subject allows the speaker to be clear and eliminates some questions the audience might have on the subject.