I answer that, The Sacrament of Baptism derives its power principally from its form, which the Apostle calls "the word of life" (Eph. 5:26). Consequently, if several were to baptize one at the same time, we must consider what form they would use. For were they to say: "We baptize thee in the name of the Father and of the Son and of the Holy Ghost," some maintain that the sacrament of Baptism would not be conferred, because the form of the Church would not be observed, i.e. "I baptize thee in the name of the Father and of the Son and of the Holy Ghost." But this reasoning is disproved by the form observed in the Greek Church. For they might say: "The servant of God, N . . ., is baptized in the name of the Father and of the Son and of the Holy Ghost," under which form the Greeks receive the sacrament of Baptism: and yet this form differs far more from the form that we use, than does this: "We baptize thee."
The point to be observed, however, is this, that by this form, "We baptize thee," the intention expressed is that several concur in conferring one Baptism: and this seems contrary to the notion of a minister; for a man does not baptize save as a minister of Christ, and as standing in His place; wherefore just as there is one Christ, so should there be one minister to represent Christ. Hence the Apostle says pointedly (Eph. 4:5): "one Lord, one Faith, one Baptism." Consequently, an intention which is in opposition to this seems to annul the sacrament of Baptism.
On the other hand, if each were to say: "I baptize thee in the name of the Father and of the Son and of the Holy Ghost," each would signify his intention as though he were conferring Baptism independently of the other. This might occur in the case where both were striving to baptize someone; and then it is clear that whichever pronounced the words first would confer the sacrament of Baptism; while the other, however great his right to baptize, if he presume to utter the words, would be liable to be punished as a rebaptizer. If, however, they were to pronounce the words absolutely at the same time, and dipped or sprinkled the man together, they should be punished for baptizing in an improper manner, but not for rebaptizing: because each would intend to baptize an unbaptized person, and each, so far as he is concerned, would baptize. Nor would they confer several sacraments: but the one Christ baptizing inwardly would confer one sacrament by means of both together.