I answer that, With regard to all the variations that may occur in the sacramental forms, two points seem to call for our attention. one is on the part of the person who says the words, and whose intention is essential to the sacrament, as will be explained further on (Question [64], Article [8]). Wherefore if he intends by such addition or suppression to perform a rite other from that which is recognized by the Church, it seems that the sacrament is invalid: because he seems not to intend to do what the Church does.
The other point to be considered is the meaning of the words. For since in the sacraments, the words produce an effect according to the sense which they convey, as stated above (Article [7], ad 1), we must see whether the change of words destroys the essential sense of the words: because then the sacrament is clearly rendered invalid. Now it is clear, if any substantial part of the sacramental form be suppressed, that the essential sense of the words is destroyed; and consequently the sacrament is invalid. Wherefore Didymus says (De Spir. Sanct. ii): "If anyone attempt to baptize in such a way as to omit one of the aforesaid names," i.e. of the Father, Son, and Holy Ghost, "his baptism will be invalid." But if that which is omitted be not a substantial part of the form, such an omission does not destroy the essential sense of the words, nor consequently the validity of the sacrament. Thus in the form of the Eucharist---"For this is My Body," the omission of the word "for" does not destroy the essential sense of the words, nor consequently cause the sacrament to be invalid; although perhaps he who makes the omission may sin from negligence or contempt.
Again, it is possible to add something that destroys the essential sense of the words: for instance, if one were to say: "I baptize thee in the name of the Father Who is greater, and of the Son Who is less," with which form the Arians baptized: and consequently such an addition makes the sacrament invalid. But if the addition be such as not to destroy the essential sense, the sacrament is not rendered invalid. Nor does it matter whether this addition be made at the beginning, in the middle, or at the end: For instance, if one were to say, "I baptize thee in the name of the Father Almighty, and of the only Begotten Son, and of the Holy Ghost, the Paraclete," the baptism would be valid; and in like manner if one were to say, "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost"; and may the Blessed Virgin succour thee, the baptism would be valid.
Perhaps, however, if one were to say, "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost, and of the Blessed Virgin Mary," the baptism would be void; because it is written (1 Cor. 1:13): "Was Paul crucified for you or were you baptized in the name of Paul?" But this is true if the intention be to baptize in the name of the Blessed Virgin as in the name of the Trinity, by which baptism is consecrated: for such a sense would be contrary to faith, and would therefore render the sacrament invalid: whereas if the addition, "and in the name of the Blessed Virgin" be understood, not as if the name of the Blessed Virgin effected anything in baptism, but as intimating that her intercession may help the person baptized to preserve the baptismal grace, then the sacrament is not rendered void.
