Q: Whether This Is the Proper Form for the Consecration of the Bread: "This Is My Body"?

A: 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.

And since the conversion is expressed in this form as in
being,
it is necessary for the extremes of the conversion to be signified as they exist in the fact of conversion. But then the term
whereunto
has the proper nature of its own substance; whereas the term
whence
does not remain in its own substance, but only as to the accidents whereby it comes under the senses, and can be determined in relation to the senses. Hence the term
whence
of the conversion is conveniently expressed by the demonstrative pronoun, relative to the sensible accidents which continue; but the term
whereunto
is expressed by the noun signifying the nature of the thing which terminates the conversion, and this is Christ's entire body, and not merely His flesh; as was said above (Q. 76, A. 1, ad 2). Hence this form is most appropriate: "This is My body."

Reply Obj. 1: The ultimate effect of this conversion is not a
becoming
but a being, as stated above, and consequently prominence should be given to this in the form.

Reply Obj. 2: God's word operated in the creation of things, and it is the same which operates in this consecration, yet each in different fashion: because here it operates effectively and sacramentally, that is, in virtue of its signification. And consequently the last effect of the consecration must needs be signified in this sentence by a substantive verb of the indicative mood and present time. But in the creation of things it worked merely effectively, and such efficiency is due to the command of His wisdom; and therefore in the creation of things the Lord's word is expressed by a verb in the imperative mood, as in Gen. 1:3: "Let there be light, and light was made."

Reply Obj. 3: The term
whence
does not retain the nature of its substance in the being of the conversion, as the term whereunto does. Therefore there is no parallel.

Reply Obj. 4: The pronoun "My," which implicitly points to the chief person, i.e. the person of the speaker, sufficiently indicates Christ's person, in Whose person these words are uttered, as stated above (A. 1).

Reply Obj. 5: The conjunction "for" is set in this form according to the custom of the Roman Church, who derived it from Peter the Apostle; and this on account of the sequence with the words preceding: and therefore it is not part of the form, just as the words preceding the form are not.