SECOND ARTICLE [III, Q. 78, Art. 2]
Whether This Is the Proper Form for the Consecration of the Bread:
"This Is My Body"?
Objection 1: It seems that this is not the proper form of this sacrament: "This is My body." For the effect of a sacrament ought to be expressed in its form. But the effect of the consecration of the bread is the change of the substance of the bread into the body of Christ, and this is better expressed by the word "becomes" than by "is." Therefore, in the form of the consecration we ought to say: "This becomes My body."
Obj. 2: Further, Ambrose says (De Sacram. iv), "Christ's words consecrate this sacrament. What word of Christ? This word, whereby all things are made. The Lord commanded, and the heavens and earth were made." Therefore, it would be a more proper form of this sacrament if the imperative mood were employed, so as to say: "Be this My body."
Obj. 3: Further, that which is changed is implied in the subject of this phrase, just as the term of the change is implied in the predicate. But just as that into which the change is made is something determinate, for the change is into nothing else but the body of Christ, so also that which is converted is determinate, since only bread is converted into the body of Christ. Therefore, as a noun is inserted on the part of the predicate, so also should a noun be inserted in the subject, so that it be said: "This bread is My body."
Obj. 4: Further, just as the term of the change is determinate in
nature, because it is a body, so also is it determinate in person.
Consequently, in order to determine the person, it ought to be said:
"This is the body of Christ."
Obj. 5: Further, nothing ought to be inserted in the form except what is substantial to it. Consequently, the conjunction "for" is improperly added in some books, since it does not belong to the substance of the form.
On the contrary, our Lord used this form in consecrating, as is evident from Matt. 26:26.
I answer that, This is the proper form for the consecration of the bread. For it was said (A. 1) that this consecration consists in changing the substance of bread into the body of Christ. Now the form of a sacrament ought to denote what is done in the sacrament. Consequently the form for the consecration of the bread ought to signify the actual conversion of the bread into the body of Christ. And herein are three things to be considered: namely, the actual conversion, the term whence, and the term whereunto.
Now the conversion can be considered in two ways: first, in becoming, secondly, in being. But the conversion ought not to be signified in this form as in becoming, but as in being. First, because such conversion is not successive, as was said above (Q. 75, A. 7), but instantaneous; and in such changes the becoming is nothing else than the being. Secondly, because the sacramental forms bear the same relation to the signification of the sacramental effect as artificial forms to the representation of the effect of art. Now an artificial form is the likeness of the ultimate effect, on which the artist's intention is fixed; just as the art-form in the builder's mind is principally the form of the house constructed, and secondarily of the constructing. Accordingly, in this form also the conversion ought to be expressed as in being, to which the intention is referred.