Objection 1. It seems that it is not lawful to add anything to the words in which the sacramental form consists. For these sacramental words are not of less importance than are the words of Holy Scripture. But it is not lawful to add anything to, or to take anything from, the words of Holy Scripture: for it is written (Deuteronomy 4:2): "You shall not add to the word that I speak to you, neither shall you take away from it"; and (Apocalypse 22:18-19): "I testify to everyone that heareth the words of the prophecy of this book: if any man shall add to these things, God shall add to him the plagues written in this book. And if any man shall take away... God shall take away his part out of the book of life." Therefore it seems that neither is it lawful to add anything to, or to take anything from, the sacramental forms.
Objection 2. Further, in the sacraments words are by way of form, as stated above (6, ad 2; 7). But any addition or subtraction in forms changes the species, as also in numbers (Metaph. viii). Therefore it seems that if anything be added to or subtracted from a sacramental form, it will not be the same sacrament.
Objection 3. Further, just as the sacramental form demands a certain number of words, so does it require that these words should be pronounced in a certain order and without interruption. If therefore, the sacrament is not rendered invalid by addition or subtraction of words, in like manner it seems that neither is it, if the words be pronounced in a different order or with interruptions.
On the contrary, Certain words are inserted by some in the sacramental forms, which are not inserted by others: thus the Latins baptize under this form: "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost"; whereas the Greeks use the following form: "The servant of God, N... is baptized in the name of the Father," etc. Yet both confer the sacrament validly. Therefore it is lawful to add something to, or to take something from, the sacramental forms.
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 (64, 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 (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 Corinthians 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.
Reply to Objection 1. It is not lawful to add anything to the words of Holy Scripture as regards the sense; but many words are added by Doctors by way of explanation of the Holy Scriptures. Nevertheless, it is not lawful to add even words to Holy Scripture as though such words were a part thereof, for this would amount to forgery. It would amount to the same if anyone were to pretend that something is essential to a sacramental form, which is not so.
Reply to Objection 2. Words belong to a sacramental form by reason of the sense signified by them. Consequently any addition or suppression of words which does not add to or take from the essential sense, does not destroy the essence of the sacrament.
Reply to Objection 3. If the words are interrupted to such an extent that the intention of the speaker is interrupted, the sacramental sense is destroyed, and consequently, the validity of the sacrament. But this is not the case if the interruption of the speaker is so slight, that his intention and the sense of the words is not interrupted.
The same is to be said of a change in the order of the words. Because if this destroys the sense of the words, the sacrament is invalidated: as happens when a negation is made to precede or follow a word. But if the order is so changed that the sense of the words does not vary, the sacrament is not invalidated, according to the Philosopher's dictum: "Nouns and verbs mean the same though they be transposed" (Peri Herm. x).
Source: Summa Theologica (New Advent)