Commentaria in Summam contra Gentiles, Liber IV

After St. Thomas has shown what the matter of the sacrament of the Eucharist is, namely that it is bread and wine, he wishes to show what sort of matter of this kind it ought to be, that is, what sort of bread and what sort of wine ¹. And he posits three conclusions.

I. The first is: Neither from any other bread than that which is made from grains of wheat, nor from any other liquid than that which is pressed from grapes, can this sacrament be confected; nor if so great an admixture of foreign matter were made to the bread and wine that the species would be dissolved.

It is proved. It is necessary that those conditions of bread and wine be preserved in this sacrament which are of the essence of bread and wine, since this sacrament is confected from bread and wine. But nothing is called wine except what is pressed from grapes, nor is anything properly called bread except what is made from grains of wheat; for others that are called breads have come into use as a supplement for bread, and likewise other liquids for the use of wine. Therefore etc.

2. It should be noted, from the doctrine of St. Thomas, Tertia, q. lxxiv ², and IV Sent., d. xi, q. ii ³, that, since that which generates generates what is like to itself in species, if there are any grains that can be generated from the seed of wheat, just as rye grows from grain sown in poor soils, bread made from such grain can be the matter of this sacrament, although that grain may be signified by another name on account of some diversity of accidents; for such is truly called wheaten bread, since the grain from which it is made is of the same species as the grain of wheat. But from other grains which can in no way be generated from the seed of wheat, such as barley, spelt, and spelt-wheat, bread cannot be made that is the suitable matter of this sacrament, since they are not of the same species as wheat.

3. It should be noted secondly that sometimes the corruption of the bread and wine is so great that the species is dissolved, which can be detected from the dissolution of continuity and from the change of flavor, color, and other accidents. And then the sacrament cannot be confected from such matter; just as it cannot be confected from vinegar, nor from starch, since it is made from corrupted wheat, although some say the contrary. But sometimes there is only a disposition to corruption, which some slight change of flavor indicates. And then the sacrament can be confected from such matter, as from sour wine, although the one confecting sins on account of irreverence toward the sacrament.

II. The second conclusion is: From leavened bread and from unleavened bread this sacrament can be confected.

It is proved. To be leavened or to be unleavened is not of the essence of bread, but when either exists, the species of bread is preserved. Therefore etc. — The consequence is proved. Because if certain things happen to wheaten bread and true wine that are not of the essence of bread and wine, when these are omitted, the true sacrament can be confected.

The conclusion is confirmed first: because different churches have a different custom in this matter.

It is confirmed secondly: because both can be fitting to the signification of the sacrament: namely, unleavened loaves, according to Gregory in the Register ⁴, to the purity of Christ's flesh; but leavened bread to the union of the divine Word with the flesh.

III. The third conclusion is: The use of unleavened bread is more fitting to the purity of the mystical body, that is, the Church, which is configured in this sacrament. It is declared by the authority of the Apostle, I Cor. v, saying: Our Pasch etc.

IV. By this is excluded the error of those who say that this sacrament cannot be celebrated in unleavened bread. Which error is indeed also evidently destroyed by the authority of the Gospel, since in Matt. xxvi, Mark xiv, and Luke xxii it is said that the Lord ate the Passover with His disciples on the first day of the unleavened bread. For it is agreed that according to the law it was not licit for leaven to be found in the houses of the Jews on the first day of the unleavened bread, as is clear from Exodus xii. Whence, since the Lord observed the law as long as He was in the world, it is manifest that He converted unleavened bread into His body and gave it to the disciples to receive.

2. Yet some say that He, with the passion imminent, anticipated the day of the unleavened bread, and that He then used leavened bread. Which they strive to show, first, from what is said in John xiii, Before the festival day of the pasch etc. — Next, from what is said in John xviii, that on the sixth day of the week, on which Christ was crucified, the Jews did not enter into Pilate's praetorium so that they might not be defiled, but might eat the pasch. Now the unleavened bread is called the pasch. And thus it is concluded that the supper was celebrated before the unleavened bread.

3. But to this St. Thomas answers: since the feast of unleavened bread was celebrated for seven days, among which the first was holy and especially solemn among the others, namely the fifteenth of the month; and among the Jews the solemnities began from the preceding evening; on the fourteenth day at evening they began to eat the pasch, as is clear from Exodus xii, and on the same day the paschal lamb was sacrificed. Therefore the first day of unleavened bread is called by the other Evangelists the fourteenth day of the month, because at evening they ate the unleavened bread, and then the paschal lamb was sacrificed. But this, according to John, was before the festival day of the pasch, that is, before the fifteenth day, which was more solemn; on which the Jews wished to eat the pasch, that is, the unleavened loaves, but not the paschal lamb.

From these things St. Thomas infers that it is plain that Christ consecrated His body from unleavened bread; and therefore the church of the Latins reasonably uses unleavened bread in this sacrament.

IV. It should be noted, from the doctrine of St. Thomas in the places cited above ⁵, that the custom of the Greeks also has some reason: namely, both on account of the signification which Gregory touches upon, and in detestation of the heresy of the Nazarenes, or Ebionites ⁶, who mixed the legal observances with the Gospel. For in the primitive Church the Apostles celebrated in unleavened bread, and the Roman church received this custom from the Apostles, as Innocent relates ⁷; but later, when the heresy was imminent that the legal observances were to be observed together with the Gospel, the holy fathers, as Pope Leo says ⁸, lest they seem to agree with them, wished this sacrament to be confected for a time ⁹ from leavened bread. When this heresy subsequently ceased, the Roman church indeed returned to the former custom, but the Greeks wished to preserve perpetually that custom instituted for a time.

2. It should be noted further, as St. Thomas says in the places cited above, that although the sacrament can be confected in either bread, nevertheless a priest in the church of the Latins who celebrates with leavened bread would sin. For as is clear from Extra, De Celebratione missae, cap. Litteras ¹⁰, a priest is punished who presumed to celebrate in leavened bread. A Greek priest celebrating from unleavened bread in the church of the Greeks would also sin, as perverting the rite of his church.