USCCB (Questions & Answers)
Q: In the Niceno-Constantinopolitan Creed, why has "one in being with the Father" been changed to "consubstantial with the Father?"
A: The new translation is more in keeping with the ancient Latin text of the Creed and a more accurate translation.
The bishops at the Council of Nicea (AD 325), in order to ensure that Jesus was professed as the eternal Son of God, equal to the Father, stated that he is "the Son of God, begotten from the Father, the only-begotten, that is from the substance of the Father, God from God, light from light, true God from true God, begotten not made, the same substance (homoousion) with the Father..." The Creed of the Council of Constantinople (381), which is professed at all Sunday Masses and Solemnities within the Catholic Church, similarly stated: "We believe in one Lord Jesus Christ, the only Son of God, eternally begotten of the Father, God from God, Light from Light, true God from true God, begotten, not made, of the same substance (homoousion) with the Father."
When these two ancient creeds were translated into Latin, the term "homoousion" was rendered as "consubstantialem," that is, "the same substance of the Father." Prior to the Second Vatican Council, the Latin "consubstantialem" was rendered as "consubstantial" within the English translation of the Creed. Many theologians and the Holy See thought that the term "consubstantial" was more in keeping with the Latin tradition and a more literal and accurate translation than the more recent "one in being."
This is in keeping with the mind of the Congregation for Divine Worship and the Discipline of the Sacraments, which published an Instruction, entitled Liturgiam Authenticam. It stated: "Certain expressions that belong to the heritage of the whole or of a great part of the ancient Church, as well as others that have become part of the general human patrimony, are to be respected by a translation that is as literal as possible" (no. 56).