Summa Th. III EN Qu.74 a.8
Objection: 1. It seems that water ought to be added in great quantity, because as blood flowed sensibly from Christ's side, so did water: hence it is written (Jn 19,35): "He that saw it, hath given testimony." But water could not be sensibly present in this sacrament except it were used in great quantity. Consequently it seems that water ought to be added in great quantity.
2. Further, a little water mixed with much wine is corrupted. But what is corrupted no longer exists. Therefore, it is the same thing to add a little water in this sacrament as to add none. But it is not lawful to add none. Therefore, neither is it lawful to add a little.
3. Further, if it sufficed to add a little, then as a consequence it would suffice to throw one drop of water into an entire cask. But this seems ridiculous. Therefore it does not suffice for a small quantity to be added.
On the contrary It is said in the Decretals (Extra, De Celeb. Miss.): "The pernicious abuse has prevailed in your country of adding water in greater quantity than the wine, in the sacrifice, where according to the reasonable custom of the entire Church more wine than water ought to be employed."
I answer that There is a threefold opinion regarding the water added to the wine, as Pope Innocent III says in a certain Decretal. For some say that the water remains by itself when the wine is changed into blood: but such an opinion cannot stand, because in the sacrament of the altar after the consecration there is nothing else save the body and the blood of Christ. Because, as Ambrose says in De Officiis (De Mysteriis ix): "Before the blessing it is another species that is named, after the blessing the Body is signified; otherwise it would not be adored with adoration of latria." And therefore others have said that as the wine is changed into blood, so the water is changed into the water which flowed from Christ's side. But this cannot be maintained reasonably, because according to this the water would be consecrated apart from the wine, as the wine is from the bread.And therefore as he (Innocent III, Decretals, Extra, De Celeb. Miss.) says, the more probable opinion is that which holds that the water is changed into wine, and the wine into blood. Now, this could not be done unless so little water was used that it would be changed into wine. Consequently, it is always safer to add little water, especially if the wine be weak, because the sacrament could not be celebrated if there were such addition of water as to destroy the species of the wine. Hence Pope Julius I reprehends some who "keep throughout the year a linen cloth steeped in must, and at the time of sacrifice wash a part of it with water, and so make the offering."
Reply to Objection: 1. For the signification of this sacrament it suffices for the water to be appreciable by sense when it is mixed with the wine: but it is not necessary for it to be sensible after the mingling.
2. If no water were added, the signification would be utterly excluded: but when the water is changed into wine, it is signified that the people is incorporated with Christ.
3. If water were added to a cask, it would not suffice for the signification of this sacrament, but the water must be added to the wine at the actual celebration of the sacrament.
We have to consider the change of the bread and wine into the body and blood of Christ; under which head there are eight points of inquiry:
(1) Whether the substance of bread and wine remain in this sacrament after the consecration?*
(2) Whether it is annihilated?
(3) Whether it is changed into the body and blood of Christ?
(4) Whether the accidents remain after the change?
(5) Whether the substantial form remains there?
(6) Whether this change is instantaneous?
(7) Whether it is more miraculous than any other change?
(8) By what words it may be suitably expressed? [*The titles of the Articles here given were taken by St. Thomas from his Commentary on the Sentences (Sent. iv, D, 90). However, in writing the Articles he introduced a new point of inquiry, that of the First Article; and substituted another division of the matter under discussion, as may be seen by referring to the titles of the various Articles. Most editions have ignored St. Thomas's original division, and give the one to which he subsequently adhered.]
Objection: 1. It seems that the body of Christ is not in this sacrament in very truth, but only as in a figure, or sign. For it is written (Jn 6,54) that when our Lord had uttered these words: "Except you eat the flesh of the Son of Man, and drink His blood," etc., "Many of His disciples on hearing it said: 'this is a hard saying'": to whom He rejoined: "It is the spirit that quickeneth; the flesh profiteth nothing": as if He were to say, according to Augustine's exposition on Ps. 4 [*On Ps 98,9]: "Give a spiritual meaning to what I have said. You are not to eat this body which you see, nor to drink the blood which they who crucify Me are to spill. It is a mystery that I put before you: in its spiritual sense it will quicken you; but the flesh profiteth nothing."
2. Further, our Lord said (Mt 28,20): "Behold I am with you all days even to the consummation of the world." Now in explaining this, Augustine makes this observation (Tract. xxx in Joan.): "The Lord is on high until the world be ended; nevertheless the truth of the Lord is here with us; for the body, in which He rose again, must be in one place; but His truth is spread abroad everywhere." Therefore, the body of Christ is not in this sacrament in very truth, but only as in a sign.
3. Further, no body can be in several places at the one time. For this does not even belong to an angel; since for the same reason it could be everywhere. But Christ's is a true body, and it is in heaven. Consequently, it seems that it is not in very truth in the sacrament of the altar, but only as in a sign.
4. Further, the Church's sacraments are ordained for the profit of the faithful. But according to Gregory in a certain Homily (xxviii in Evang.), the ruler is rebuked "for demanding Christ's bodily presence." Moreover the apostles were prevented from receiving the Holy Ghost because they were attached to His bodily presence, as Augustine says on Jn 16,7: "Except I go, the Paraclete will not come to you" (Tract. xciv in Joan.). Therefore Christ is not in the sacrament of the altar according to His bodily presence.
On the contrary Hilary says (De Trin. viii): "There is no room for doubt regarding the truth of Christ's body and blood; for now by our Lord's own declaring and by our faith His flesh is truly food, and His blood is truly drink." And Ambrose says (De Sacram. vi): "As the Lord Jesus Christ is God's true Son so is it Christ's true flesh which we take, and His true blood which we drink."
I answer that The presence of Christ's true body and blood in this sacrament cannot be detected by sense, nor understanding, but by faith alone, which rests upon Divine authority. Hence, on Lc 22,19: "This is My body which shall be delivered up for you," Cyril says: "Doubt not whether this be true; but take rather the Saviour's words with faith; for since He is the Truth, He lieth not."Now this is suitable, first for the perfection of the New Law. For, the sacrifices of the Old Law contained only in figure that true sacrifice of Christ's Passion, according to He 10,1: "For the law having a shadow of the good things to come, not the very image of the things." And therefore it was necessary that the sacrifice of the New Law instituted by Christ should have something more, namely, that it should contain Christ Himself crucified, not merely in signification or figure, but also in very truth. And therefore this sacrament which contains Christ Himself, as Dionysius says (Eccl. Hier. iii), is perfective of all the other sacraments, in which Christ's virtue is participated.Secondly, this belongs to Christ's love, out of which for our salvation He assumed a true body of our nature. And because it is the special feature of friendship to live together with friends, as the Philosopher says (Ethic. ix), He promises us His bodily presence as a reward, saying (Mt 24,28): "Where the body is, there shall the eagles be gathered together." Yet meanwhile in our pilgrimage He does not deprive us of His bodily presence; but unites us with Himself in this sacrament through the truth of His body and blood. Hence (Jn 6,57) he says: "He that eateth My flesh, and drinketh My blood, abideth in Me, and I in him." Hence this sacrament is the sign of supreme charity, and the uplifter of our hope, from such familiar union of Christ with us.Thirdly, it belongs to the perfection of faith, which concerns His humanity just as it does His Godhead, according to Jn 14,1: "You believe in God, believe also in Me." And since faith is of things unseen, as Christ shows us His Godhead invisibly, so also in this sacrament He shows us His flesh in an invisible manner.Some men accordingly, not paying heed to these things, have contended that Christ's body and blood are not in this sacrament except as in a sign, a thing to be rejected as heretical, since it is contrary to Christ's words. Hence Berengarius, who had been the first deviser of this heresy, was afterwards forced to withdraw his error, and to acknowledge the truth of the faith.
Reply to Objection: 1. From this authority the aforesaid heretics have taken occasion to err from evilly understanding Augustine's words. For when Augustine says: "You are not to eat this body which you see," he means not to exclude the truth of Christ's body, but that it was not to be eaten in this species in which it was seen by them. And by the words: "It is a mystery that I put before you; in its spiritual sense it will quicken you," he intends not that the body of Christ is in this sacrament merely according to mystical signification, but "spiritually," that is, invisibly, and by the power of the spirit. Hence (Tract. xxvii), expounding Jn 6,64: "the flesh profiteth nothing," he says: "Yea, but as they understood it, for they understood that the flesh was to be eaten as it is divided piecemeal in a dead body, or as sold in the shambles, not as it is quickened by the spirit . . . Let the spirit draw nigh to the flesh . . . then the flesh profiteth very much: for if the flesh profiteth nothing, the Word had not been made flesh, that It might dwell among us."
2. That saying of Augustine and all others like it are to be understood of Christ's body as it is beheld in its proper species; according as our Lord Himself says (Mt 26,11): "But Me you have not always." Nevertheless He is invisibly under the species of this sacrament, wherever this sacrament is performed.
3. Christ's body is not in this sacrament in the same way as a body is in a place, which by its dimensions is commensurate with the place; but in a special manner which is proper to this sacrament. Hence we say that Christ's body is upon many altars, not as in different places, but "sacramentally": and thereby we do not understand that Christ is there only as in a sign, although a sacrament is a kind of sign; but that Christ's body is here after a fashion proper to this sacrament, as stated above.
4. This argument holds good of Christ's bodily presence, as He is present after the manner of a body, that is, as it is in its visible appearance, but not as it is spiritually, that is, invisibly, after the manner and by the virtue of the spirit. Hence Augustine (Tract. xxvii in Joan.) says: "If thou hast understood" Christ's words spiritually concerning His flesh, "they are spirit and life to thee; if thou hast understood them carnally, they are also spirit and life, but not to thee."
Objection: 1. It seems that the substance of the bread and wine does remain in this sacrament after the consecration: because Damascene says (De Fide Orth. iv): "Since it is customary for men to eat bread and drink wine, God has wedded his Godhead to them, and made them His body and blood": and further on: "The bread of communication is not simple bread, but is united to the Godhead." But wedding together belongs to things actually existing. Therefore the bread and wine are at the same time, in this sacrament, with the body and the blood of Christ.
2. Further, there ought to be conformity between the sacraments. But in the other sacraments the substance of the matter remains, like the substance of water in Baptism, and the substance of chrism in Confirmation. Therefore the substance of the bread and wine remains also in this sacrament.
3. Further, bread and wine are made use of in this sacrament, inasmuch as they denote ecclesiastical unity, as "one bread is made from many grains and wine from many grapes," as Augustine says in his book on the Creed (Tract. xxvi in Joan.). But this belongs to the substance of bread and wine. Therefore, the substance of the bread and wine remains in this sacrament.
On the contrary Ambrose says (De Sacram. iv): "Although the figure of the bread and wine be seen, still, after the Consecration, they are to be believed to be nothing else than the body end blood of Christ."
I answer that Some have held that the substance of the bread and wine remains in this sacrament after the consecration. But this opinion cannot stand: First of all, because by such an opinion the truth of this sacrament is destroyed, to which it belongs that Christ's true body exists in this sacrament; which indeed was not there before the consecration. Now a thing cannot be in any place, where it was not previously, except by change of place, or by the conversion of another thing into itself; just as fire begins anew to be in some house, either because it is carried thither, or because it is generated there. Now it is evident that Christ's body does not begin to be present in this sacrament by local motion. First of all, because it would follow that it would cease to be in heaven: for what is moved locally does not come anew to some place unless it quit the former one. Secondly, because every body moved locally passes through all intermediary spaces, which cannot be said here. Thirdly, because it is not possible for one movement of the same body moved locally to be terminated in different places at the one time, whereas the body of Christ under this sacrament begins at the one time to be in several places. And consequently it remains that Christ's body cannot begin to be anew in this sacrament except by change of the substance of bread into itself. But what is changed into another thing, no longer remains after such change. Hence the conclusion is that, saving the truth of this sacrament, the substance of the bread cannot remain after the consecration.Secondly, because this position is contrary to the form of this sacrament, in which it is said: "This is My body," which would not be true if the substance of the bread were to remain there; for the substance of bread never is the body of Christ. Rather should one say in that case: "Here is My body."Thirdly, because it would be opposed to the veneration of this sacrament, if any substance were there, which could not be adored with adoration of latria.Fourthly, because it is contrary to the rite of the Church, according to which it is not lawful to take the body of Christ after bodily food, while it is nevertheless lawful to take one consecrated host after another. Hence this opinion is to be avoided as heretical.
Reply to Objection: 1. God "wedded His Godhead," i.e. His Divine power, to the bread and wine, not that these may remain in this sacrament, but in order that He may make from them His body and blood.
2. Christ is not really present in the other sacraments, as in this; and therefore the substance of the matter remains in the other sacraments, but not in this.
3. The species which remain in this sacrament, as shall be said later (Article ), suffice for its signification; because the nature of the substance is known by its accidents.
Objection: 1. It seems that the substance of the bread is annihilated after the consecration of this sacrament, or dissolved into its original matter. For whatever is corporeal must be somewhere. But the substance of bread, which is something corporeal, does not remain, in this sacrament, as stated above (Article ); nor can we assign any place where it may be. Consequently it is nothing after the consecration. Therefore, it is either annihilated, or dissolved into its original matter.
2. Further, what is the term "wherefrom" in every change exists no longer, except in the potentiality of matter; e.g. when air is changed into fire, the form of the air remains only in the potentiality of matter; and in like fashion when what is white becomes black. But in this sacrament the substance of the bread or of the wine is the term "wherefrom," while the body or the blood of Christ is the term "whereunto": for Ambrose says in De Officiis (De Myster. ix): "Before the blessing it is called another species, after the blessing the body of Christ is signified." Therefore, when the consecration takes place, the substance of the bread or wine no longer remains, unless perchance dissolved into its (original) matter.
3. Further, one of two contradictories must be true. But this proposition is false: "After the consecration the substance of the bread or wine is something." Consequently, this is true: "The substance of the bread or wine is nothing."
On the contrary Augustine says (Question ): "God is not the cause of tending to nothing." But this sacrament is wrought by Divine power. Therefore, in this sacrament the substance of the bread or wine is not annihilated.
I answer that Because the substance of the bread and wine does not remain in this sacrament, some, deeming that it is impossible for the substance of the bread and wine to be changed into Christ's flesh and blood, have maintained that by the consecration, the substance of the bread and wine is either dissolved into the original matter, or that it is annihilated.Now the original matter into which mixed bodies can be dissolved is the four elements. For dissolution cannot be made into primary matter, so that a subject can exist without a form, since matter cannot exist without a form. But since after the consecration nothing remains under the sacramental species except the body and the blood of Christ, it will be necessary to say that the elements into which the substance of the bread and wine is dissolved, depart from thence by local motion, which would be perceived by the senses. In like manner also the substance of the bread or wine remains until the last instant of the consecration; but in the last instant of the consecration there is already present there the substance of the body or blood of Christ, just as the form is already present in the last instant of generation. Hence no instant can be assigned in which the original matter can be there. For it cannot be said that the substance of the bread or wine is dissolved gradually into the original matter, or that it successively quits the species, for if this began to be done in the last instant of its consecration, then at the one time under part of the host there would be the body of Christ together with the substance of bread, which is contrary to what has been said above (Article ). But if this begin to come to pass before the consecration, there will then be a time in which under one part of the host there will be neither the substance of bread nor the body of Christ, which is not fitting. They seem indeed to have taken this into careful consideration, wherefore they formulated their proposition with an alternative viz. that (the substance) may be annihilated. But even this cannot stand, because no way can be assigned whereby Christ's true body can begin to be in this sacrament, except by the change of the substance of bread into it, which change is excluded the moment we admit either annihilation of the substance of the bread, or dissolution into the original matter. Likewise no cause can be assigned for such dissolution or annihilation, since the effect of the sacrament is signified by the form: "This is My body." Hence it is clear that the aforesaid opinion is false.
Reply to Objection: 1. The substance of the bread or wine, after the consecration, remains neither under the sacramental species, nor elsewhere; yet it does not follow that it is annihilated; for it is changed into the body of Christ; just as if the air, from which fire is generated, be not there or elsewhere, it does not follow that it is annihilated.
2. The form, which is the term "wherefrom," is not changed into another form; but one form succeeds another in the subject; and therefore the first form remains only in the potentiality of matter. But here the substance of the bread is changed into the body of Christ, as stated above. Hence the conclusion does not follow.
3. Although after the consecration this proposition is false: "The substance of the breed is something," still that into which the substance of the bread is changed, is something, and consequently the substance of the bread is not annihilated.
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.
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.
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 (Article ), 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 (Article , 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 Jn 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 the I 7,1; Question , Article ; 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.
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.
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.
Objection: 1. It seems that the accidents of the bread and wine do not remain in this sacrament. For when that which comes first is removed, that which follows is also taken away. But substance is naturally before accident, as is proved in Metaph. vii. Since, then, after consecration, the substance of the bread does not remain in this sacrament, it seems that its accidents cannot remain.
2. Further, there ought not to be any deception in a sacrament of truth. But we judge of substance by accidents. It seems, then, that human judgment is deceived, if, while the accidents remain, the substance of the bread does not. Consequently this is unbecoming to this sacrament.
3. Further, although our faith is not subject to reason, still it is not contrary to reason, but above it, as was said in the beginning of this work (I 1,6, ad 2; Article ). But our reason has its origin in the senses. Therefore our faith ought not to be contrary to the senses, as it is when sense judges that to be bread which faith believes to be the substance of Christ's body. Therefore it is not befitting this sacrament for the accidents of bread to remain subject to the senses, and for the substance of bread not to remain.
4. Further, what remains after the change has taken place seems to be the subject of change. If therefore the accidents of the bread remain after the change has been effected, it seems that the accidents are the subject of the change. But this is impossible; for "an accident cannot have an accident" (Metaph. iii). Therefore the accidents of the bread and wine ought not to remain in this sacrament.
On the contrary Augustine says in his book on the Sentences of Prosper (Lanfranc, De Corp. et Sang. Dom. xiii): "Under the species which we behold, of bread and wine, we honor invisible things, i.e. flesh and blood."
I answer that It is evident to sense that all the accidents of the bread and wine remain after the consecration. And this is reasonably done by Divine providence. First of all, because it is not customary, but horrible, for men to eat human flesh, and to drink blood. And therefore Christ's flesh and blood are set before us to be partaken of under the species of those things which are the more commonly used by men, namely, bread and wine. Secondly, lest this sacrament might be derided by unbelievers, if we were to eat our Lord under His own species. Thirdly, that while we receive our Lord's body and blood invisibly, this may redound to the merit of faith.
Reply to Objection: 1. As is said in the book De Causis, an effect depends more on the first cause than on the second. And therefore by God's power, which is the first cause of all things, it is possible for that which follows to remain, while that which is first is taken away.
2. There is no deception in this sacrament; for the accidents which are discerned by the senses are truly present. But the intellect, whose proper object is substance as is said in De Anima iii, is preserved by faith from deception.
3. And this serves as answer to the third argument; because faith is not contrary to the senses, but concerns things to which sense does not reach.
4. This change has not properly a subject, as was stated above (Article , ad 1); nevertheless the accidents which remain have some resemblance of a subject.
Objection: 1. It seems that the substantial form of the bread remains in this sacrament after the consecration. For it has been said (Article ) that the accidents remain after the consecration. But since bread is an artificial thing, its form is an accident. Therefore it remains after the consecration.
2. Further, the form of Christ's body is His soul: for it is said in De Anima ii, that the soul "is the act of a physical body which has life in potentiality". But it cannot be said that the substantial form of the bread is changed into the soul. Therefore it appears that it remains after the consecration.
3. Further, the proper operation of a things follows its substantial form. But what remains in this sacrament, nourishes, and performs every operation which bread would do were it present. Therefore the substantial form of the bread remains in this sacrament after the consecration.
On the contrary The substantial form of bread is of the substance of bread. But the substance of the bread is changed into the body of Christ, as stated above (Articles ,3,4). Therefore the substantial form of the bread does not remain.
I answer that Some have contended that after the consecration not only do the accidents of the bread remain, but also its substantial form. But this cannot be. First of all, because if the substantial form of the bread were to remain, nothing of the bread would be changed into the body of Christ, excepting the matter; and so it would follow that it would be changed, not into the whole body of Christ, but into its matter, which is repugnant to the form of the sacrament, wherein it is said: "This is My body."Secondly, because if the substantial form of the bread were to remain, it would remain either in matter, or separated from matter. The first cannot be, for if it were to remain in the matter of the bread, then the whole substance of the bread would remain, which is against what was said above (Article ). Nor could it remain in any other matter, because the proper form exists only in its proper matter. But if it were to remain separate from matter, it would then be an actually intelligible form, and also an intelligence; for all forms separated from matter are such.Thirdly, it would be unbefitting this sacrament: because the accidents of the bread remain in this sacrament, in order that the body of Christ may be seen under them, and not under its proper species, as stated above (Article ).And therefore it must be said that the substantial form of the bread does not remain.
Reply to Objection: 1. There is nothing to prevent art from making a thing whose form is not an accident, but a substantial form; as frogs and serpents can be produced by art: for art produces such forms not by its own power, but by the power of natural energies. And in this way it produces the substantial forms of bread, by the power of fire baking the matter made up of flour and water.
2. The soul is the form of the body, giving it the whole order of perfect being, i.e. being, corporeal being, and animated being, and so on. Therefore the form of the bread is changed into the form of Christ's body, according as the latter gives corporeal being, but not according as it bestows animated being.
3. Some of the operations of bread follow it by reason of the accidents, such as to affect the senses, and such operations are found in the species of the bread after the consecration on account of the accidents which remain. But some other operations follow the bread either by reason of the matter, such as that it is changed into something else, or else by reason of the substantial form, such as an operation consequent upon its species, for instance, that it "strengthens man's heart" (Ps 103,15); and such operations are found in this sacrament, not on account of the form or matter remaining, but because they are bestowed miraculously upon the accidents themselves, as will be said later (Question , Article , ad 2,3; Articles ,6).
Summa Th. III EN Qu.74 a.8