"you are one God, you are one Lord: not in the singularity of one person, but in a Trinity of one substance."

"It is truly right and just,
our duty and our salvation,
always and everywhere to give you thanks,
Lord, holy Father, almighty and eternal God.
For with your Only Begotten Son and the Holy Spirit
you are one God, you are one Lord:
not in the singularity of one person,
but in a Trinity of one substance.
For what, of your glory, you revealing, we believe,
that of your Son,
that of your Holy Spirit,
without distinction we feel/experience/think/declare.
So that, in the confession of your true and eternal Deity/Godhead,
the peculiarity in Persons,
the unity in essence,
and the equality in majesty is adored.
Which/whom the angels and archangels praise,
the cherubim, too, and the seraphim,
who do not cease to cry out each day,
with one voice saying:"

. . .
Qui cum Unigenito Filio tuo et Spiritu Sancto
unus es Deus, unus es Dominus:
non in unius singularitate personae,
sed in unius Trinitate substantiae.
Quod enim de tua gloria, revelante te, credimus,
hoc de Filio tuo,
hoc de Spiritu Sancto,
sine discretione sentimus,
Ut in confessione verae sempiternaeque Deitatis,
et in personis proprietas,
et in essential unitas,
et in maiestate adoretur aequalitas.
. . .

2010 translation:
"It is truly right and just,
our duty and our salvation,
always and everywhere to give you thanks,
Lord, holy Father, almighty and eternal God.
For with your Only Begotten Son and the Holy Spirit
you are one God, one Lord:
not in the unity of a single person,
but in a Trinity of one substance.
For what you have revealed to us of your glory
we believe equally of your Son and of the Holy Spirit,
so that, in the confessing of the true and eternal Godhead,
you might be adored in what is proper to each Person,
their unity in substance,
and their equality in majesty.
For this is praised by Angels and Archangels,
Cherubim, too, and Seraphim,
who never cease to cry out each day,
as with one voice they acclaim:"

Earlier "translation":
"Father, all-powerful and ever-living God, we do well always and everywhere to give you thanks.
"We joyfully proclaim our faith in the mystery of your Godhead.  You have revealed your glory as the glory also of your Son and of the Holy Spirit:  three Persons equal in majesty, undivided in splendor, yet one Lord, one God, ever to be adored in your everlasting glory.
"And so, with all the choirs of angels in heaven we proclaim your glory and join in their unending hymn of praise."

1979 Book of common prayer, Rite II:
"For with your co-eternal Son and Holy Spirit, you are one God, one Lord, in Trinity of persons and in Unity of Being; and we celebrate the one and eternal glory of you, O Father, and of the Son, and of the Holy Spirit."

1979 Book of common prayer, Rite I:
"For with thy co-eternal Son and Holy Spirit, thou art one God, one Lord, in Trinity of Persons and in Unity of Substance; and we celebrate the one and eternal glory of thee, O Father and of the Son, and of the Holy Spirit."

1928 Book of common prayer:
"Who, with thine only-begotten Son, and the Holy Ghost, art one God, one Lord, in Trinity of Persons and in Unity of Substance.  For that which we believe of thy glory, O Father, the same we believe of the Son, and of the Holy Ghost, without any difference of inequality."

1549 Book of common prayer (undoubtedly modernized):
"Which art one  God, one Lord, not one only person, but three persons in one substance:  For that which we believe of the glory of the Father, the same we believe of the Son, and of the Holy Ghost, without any difference or inequality:  whom the angels. . . ."


     Preface for the Feast of the Most Holy Trinity, Roman missal.  This Preface was lifted directly out of the 8th-century Old Gelasian (GelV) sacramentary, where (in the edition of Mohlberg, Einzenhöfer, & Siffrin) it is no. 680 (ed. Wilson, LXXXIV, p. 129).  Also Gregorian (no. 1621).  And so forth.  For a bit more on this, see Hatchett, pp. 402-403.  The term "singularitas" is there (among the sources listed by Ward & Johnson) in Fulgentius Ferrandus Ep. 3.1:  "Plurimos vero personae unius singularitas ab opinione duarum substantiarum terret incautos."