What is transubstantiation?
In short: Transubstantiation is the Church's term for what happens at Mass when the substance of bread and wine is completely changed into the Body and Blood of Jesus Christ, while the outward appearances of bread and wine remain unchanged.
At every Catholic Mass, during the Liturgy of the Eucharist, the priest speaks the words of consecration over the bread and the cup of wine. Catholics believe something extraordinary happens in that moment: the bread and wine do not merely symbolise Christ, nor does Christ simply accompany them as a guest alongside the bread. Rather, the very substance of the bread ceases to exist and the very substance of the wine ceases to exist, and in their place stands the Body, Blood, Soul, and Divinity of Jesus Christ. The outward appearances, what philosophers call the accidents, remain: the colour, shape, taste, and feel of bread and wine persist. But what those appearances now present to the world is Christ himself.
The word transubstantiation comes from the Latin trans (across, through) and substantia (substance, the underlying reality of a thing). The Church chose this philosophical vocabulary to express a truth that goes beyond ordinary change. When water becomes ice, the outward form shifts but the underlying substance (H₂O) stays the same. Transubstantiation is the reverse: the appearances stay, and the underlying reality, the substance, is wholly converted. The Council of Trent, whose definition the Catechism of the Catholic Church quotes, called it 'a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood' (CCC 1376). This, the Council added, the holy Catholic Church has 'fittingly and properly called transubstantiation.'
The Church grounds this teaching first in Scripture, above all in John 6, where Jesus says 'my flesh is true food and my blood is true drink' (Jn 6:55), and in the words of institution at the Last Supper recorded in the Synoptic Gospels and by St Paul: 'This is my body ... This cup is the new covenant in my blood' (1 Cor 11:24-25). The Fathers of the Church took these words to heart from the earliest centuries. St John Chrysostom taught that it is not the priest who causes the gifts to become the Body and Blood of Christ, but Christ himself, who was crucified for us. St Ambrose insisted that 'the power of the blessing prevails over that of nature' (cf. CCC 1375). The Catholic tradition has never read these words as mere metaphor.
Because Christ is wholly present, Body, Blood, Soul, and Divinity, under each species separately, a person who receives only the consecrated bread receives the whole Christ, not a part of him. The same holds true for the smallest fragment: 'Christ is present whole and entire in each of the species and whole and entire in each of their parts, in such a way that the breaking of the bread does not divide Christ' (CCC 1377). This is why Catholics genuflect before the tabernacle, where consecrated hosts are reserved: they are bowing before a Person, not an object. Adoration of the Blessed Sacrament, such as Exposition and Benediction, flows naturally from this belief, because to adore the Eucharist is simply to acknowledge who is there.
Transubstantiation is not a medieval invention so much as a precision. The Church identified the word in the twelfth century and the Council of Trent defined it dogmatically in 1551 in response to Reformation disputes, but the underlying conviction, that the Eucharist is truly the Body and Blood of Christ, belongs to the Church from the beginning. The Eucharist is the 'source and summit of the Christian life' (CCC 1324), the sacrament toward which all others point. If you would like to encounter this mystery for yourself, you are welcome to find a Catholic Mass near you and attend as a guest. Catholics preparing to receive the Eucharist can also explore confession times, since the Church asks the faithful to be in a state of grace before receiving Holy Communion.
What the Catechism says
Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy Council now declares again, that by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation.
The Eucharistic presence of Christ begins at the moment of the consecration and endures as long as the Eucharistic species subsist. Christ is present whole and entire in each of the species and whole and entire in each of their parts, in such a way that the breaking of the bread does not divide Christ.
The mode of Christ's presence under the Eucharistic species is unique. It raises the Eucharist above all the sacraments as 'the perfection of the spiritual life and the end to which all the sacraments tend.' In the most blessed sacrament of the Eucharist 'the body and blood, together with the soul and divinity, of our Lord Jesus Christ and, therefore, the whole Christ is truly, really, and substantially contained.'
By the consecration the transubstantiation of the bread and wine into the Body and Blood of Christ is brought about. Under the consecrated species of bread and wine Christ himself, living and glorious, is present in a true, real, and substantial manner: his Body and his Blood, with his soul and his divinity (cf. Council of Trent: DS 1640; 1651).
In Sacred Scripture
- John 6:55 — Jesus declares: 'my flesh is true food, and my blood is true drink' - the Bread of Life discourse that grounds the Real Presence.
- 1 Corinthians 11:24-25 — Paul transmits the words of institution: 'This is my body' and 'This cup is the new covenant in my blood,' the earliest written record of the Last Supper.
- Matthew 26:26-28 — At the Last Supper Jesus takes bread and says 'This is my body' and over the cup 'This is my blood of the covenant.'
- Luke 22:19-20 — The Lukan account of institution adds 'Do this in memory of me,' establishing the Eucharist as a perpetual act of the Church.
Frequently Asked Questions
Do Catholics believe the bread and wine literally become Jesus?
Yes. Catholic teaching holds that the substance, the underlying reality, of the bread and wine is wholly changed into the Body and Blood of Christ at the moment of consecration. The appearances of bread and wine remain, but what is truly present is Christ himself: Body, Blood, Soul, and Divinity. This is not symbolic or merely spiritual; the Church teaches it as a real, substantial presence (CCC 1374, 1413).
If it really becomes Christ, why does it still look and taste like bread?
The Church distinguishes between a thing's outward appearances (colour, shape, taste, texture, what philosophers call accidents) and its underlying substance (what the thing actually is). At the consecration the substance changes entirely, but the appearances remain. This is what makes transubstantiation unique: in ordinary change the substance stays and the form changes, whereas here the form stays and the substance is wholly converted.
When does transubstantiation happen at Mass?
It happens at the moment the priest speaks the words of consecration: 'This is my Body' over the bread and 'This is the chalice of my Blood' over the wine. The Catechism teaches that the Eucharistic presence of Christ begins at the moment of the consecration and endures as long as the Eucharistic species subsist (CCC 1377), which is why consecrated hosts reserved in the tabernacle are treated with the same reverence as Christ himself.