from the

Summa Theologiae

of Thomas Aquinas (d. 1274) 

3.75.4 Whether bread can be converted into the body of Christ?

Objection 1. It seems that bread cannot be converted into the body of Christ. For conversion is a kind of change. But in every change there must be some subject, which from being previously in potentiality is now in act. because as is said in Phys. iii: "motion is the act of a thing existing in potentiality." But no subject can be assigned for the substance of the bread and of the body of Christ, because it is of the very nature of substance for it "not to be in a subject," as it is said in Praedic. iii. Therefore it is not possible for the whole substance of the bread to be converted into the body of Christ.

Objection 2. Further, the form of the thing into which another is converted, begins anew to inhere in the matter of the thing converted into it: as when air is changed into fire not already existing, the form of fire begins anew to be in the matter of the air; and in like manner when food is converted into non-pre-existing man, the form of the man begins to be anew in the matter of the food. Therefore, if bread be changed into the body of Christ, the form of Christ's body must necessarily begin to be in the matter of the bread, which is false. Consequently, the bread is not changed into the substance of Christ's body.

Objection 3. Further, when two things are diverse, one never becomes the other, as whiteness never becomes blackness, as is stated in Phys. i. But since two contrary forms are of themselves diverse, as being the principles of formal difference, so two signate matters are of themselves diverse, as being the principles of material distinction. Consequently, it is not possible for this matter of bread to become this matter whereby Christ's body is individuated, and so it is not possible for this substance of bread to be changed into the substance of Christ's body.

On the contrary, Eusebius Emesenus says: "To thee it ought neither to be a novelty nor an impossibility that earthly and mortal things be changed into the substance of Christ."

I answer that, As stated above (2), since Christ's true body is in this sacrament, and since it does not begin to be there by local motion, nor is it contained therein as in a place, as is evident from what was stated above (1, ad 2), it must be said then that it begins to be there by conversion of the substance of bread into itself.

Yet this change is not like natural changes, but is entirely supernatural, and effected by God's power alone. Hence Ambrose says [(De Sacram. iv): "See how Christ's word changes nature's laws, as He wills: a man is not wont to be born save of man and woman: see therefore that against the established law and order a man is born of a Virgin": and] [The passage in the brackets is not in the Leonine edition] (De Myster. iv): "It is clear that a Virgin begot beyond the order of nature: and what we make is the body from the Virgin. Why, then, do you look for nature's order in Christ's body, since the Lord Jesus was Himself brought forth of a Virgin beyond nature?" Chrysostom likewise (Hom. xlvii), commenting on John 6:64: "The words which I have spoken to you," namely, of this sacrament, "are spirit and life," says: i.e. "spiritual, having nothing carnal, nor natural consequence; but they are rent from all such necessity which exists upon earth, and from the laws here established."

For it is evident that every agent acts according as it is in act. But every created agent is limited in its act, as being of a determinate genus and species: and consequently the action of every created agent bears upon some determinate act. Now the determination of every thing in actual existence comes from its form. Consequently, no natural or created agent can act except by changing the form in something; and on this account every change made according to nature's laws is a formal change. But God is infinite act, as stated in I, 7, 1; 26, 2; hence His action extends to the whole nature of being. Therefore He can work not only formal conversion, so that diverse forms succeed each other in the same subject; but also the change of all being, so that, to wit, the whole substance of one thing be changed into the whole substance of another. And this is done by Divine power in this sacrament; for the whole substance of the bread is changed into the whole substance of Christ's body, and the whole substance of the wine into the whole substance of Christ's blood. Hence this is not a formal, but a substantial conversion; nor is it a kind of natural movement: but, with a name of its own, it can be called "transubstantiation."

Reply to Objection 1. This objection holds good in respect of formal change, because it belongs to a form to be in matter or in a subject; but it does not hold good in respect of the change of the entire substance. Hence, since this substantial change implies a certain order of substances, one of which is changed into the other, it is in both substances as in a subject, just as order and number.

Reply to Objection 2. This argument also is true of formal conversion or change, because, as stated above (ad 1), a form must be in some matter or subject. But this is not so in a change of the entire substance; for in this case no subject is possible.

Reply to Objection 3. Form cannot be changed into form, nor matter into matter by the power of any finite agent. Such a change, however, can be made by the power of an infinite agent, which has control over all being, because the nature of being is common to both forms and to both matters; and whatever there is of being in the one, the author of being can change into whatever there is of being in the other, withdrawing that whereby it was distinguished from the other.

3.83.1 Whether Christ is sacrificed in this sacrament?
Objection 1. It seems that Christ is not sacrificed in the celebration of this sacrament. For it is written (Heb. 10:14) that "Christ by one oblation hath perfected for ever them that are sanctified." But that oblation was His oblation. Therefore Christ is not sacrificed in the celebration of this sacrament.

Objection 2. Further, Christ's sacrifice was made upon the cross, whereon "He delivered Himself for us, an oblation and a sacrifice to God for an odor of sweetness," as is said in Eph. 5:2. But Christ is not crucified in the celebration of this mystery. Therefore, neither is He sacrificed.

Objection 3. Further, as Augustine says (De Trin. iv), in Christ's sacrifice the priest and the victim are one and the same. But in the celebration of this sacrament the priest and the victim are not the same. Therefore, the celebration of this sacrament is not a sacrifice of Christ.

On the contrary, Augustine says in the Liber Sentent. Prosp. (cf. Ep. xcviii): "Christ was sacrificed once in Himself, and yet He is sacrificed daily in the Sacrament."

I answer that, The celebration of this sacrament is called a sacrifice for two reasons. First, because, as Augustine says (Ad Simplician. ii), "the images of things are called by the names of the things whereof they are the images; as when we look upon a picture or a fresco, we say, 'This is Cicero and that is Sallust.'" But, as was said above (79, 1), the celebration of this sacrament is an image representing Christ's Passion, which is His true sacrifice. Accordingly the celebration of this sacrament is called Christ's sacrifice. Hence it is that Ambrose, in commenting on Heb. 10:1, says: "In Christ was offered up a sacrifice capable of giving eternal salvation; what then do we do? Do we not offer it up every day in memory of His death?" Secondly it is called a sacrifice, in respect of the effect of His Passion: because, to wit, by this sacrament, we are made partakers of the fruit of our Lord's Passion. Hence in one of the Sunday Secrets (Ninth Sunday after Pentecost) we say: "Whenever the commemoration of this sacrifice is celebrated, the work of our redemption is enacted." Consequently, according to the first reason, it is true to say that Christ was sacrificed, even in the figures of the Old Testament: hence it is stated in the Apocalypse (13:8): "Whose names are not written in the Book of Life of the Lamb, which was slain from the beginning of the world." But according to the second reason, it is proper to this sacrament for Christ to be sacrificed in its celebration.

Reply to Objection 1. As Ambrose says (commenting on Heb. 10:1), "there is but one victim," namely that which Christ offered, and which we offer, "and not many victims, because Christ was offered but once: and this latter sacrifice is the pattern of the former. For, just as what is offered everywhere is one body, and not many bodies, so also is it but one sacrifice."

Reply to Objection 2. As the celebration of this sacrament is an image representing Christ's Passion, so the altar is representative of the cross itself, upon which Christ was sacrificed in His proper species.

Reply to Objection 3. For the same reason (cf. Reply to Obj. 2) the priest also bears Christ's image, in Whose person and by Whose power he pronounces the words of consecration, as is evident from what was said above (82, 1,3). And so, in a measure, the priest and victim are one and the same.