Catechesis: Sacrament of the Altar

With heart and mouth we reject and condemn as false, erroneous, and misleading all errors that do not agree with but contradict and oppose the doctrine mentioned above and founded in God's Word, such as these: The papistic transubstantiation. It is taught that the consecrated or blessed bread and wine in the Holy Supper entirely lose their substance and essence. They are changed into the substance of Christ's body and blood in such a way that only the mere form of bread and wine is left, or the accidents without the object.—FC VII:107, 108

Cf. Certainly the sacraments of the body and blood of Christ are a divine thing, through which we are made partakers of the divine nature; and yet the substance or nature of bread and wine does not cease to be. – Pope St. Gelasius, De duabis nature. In Chr. Adv. Eutych. Et Nestor. Patrology IV, 1:422