Episode 3061: St Thomas Aquinas - Difference of Orthodox and Catholics by Sharon- Part 4

4. Latin Sacramental Practices
• Example: Use of unleavened bread in the Latin Mass.
• Eastern critics claimed this invalidated the Eucharist.
• Aquinas responded:
“It is the substance, not the accident, that pertains to the reality of the sacrament.” (Summa, III, q. 74)
The Dispute Over Unleavened Bread and the Validity of the Eucharist
One of the concrete and long-standing ritual differences between the Latin (Western) Church and the Eastern Orthodox tradition lies in the matter used for the Holy Eucharist specifically, unleavened bread versus leavened bread.
The Latin Practice: Unleavened Bread
In the Latin Church, following apostolic tradition and in remembrance of the Last Supper, the Holy Sacrifice of the Mass is celebrated using unleavened bread that is, bread made without yeast. This form, called azymes (AZ-ime), is understood to reflect the Passover setting of the Last Supper (cf. Exodus 12), where unleavened bread was prescribed and symbolized purity, haste, and the absence of corruption.
Eastern Criticism: A Challenge to Validity
Some Eastern theologians, particularly during the medieval period and in polemical writings around the time of the Great Schism (1054), went so far as to criticize the Latin use of unleavened bread, claiming that it invalidated the Eucharist.
Their arguments included:
• Apostolic Tradition: That leavened bread (artos) was always used in the early Church and is more appropriate to represent the Risen Christ.
• Symbolism: That yeast represents the life-giving power of the Resurrection, whereas unleavened bread is considered “dead” bread.
• Accusations: Some even accused the Latin Church of being Judaizing, overly fixated on the Passover and Old Law.
These critiques were not merely ritual complaints but often charged the Latins with heresy or liturgical innovation, suggesting that the form used rendered the Latin Mass illicit or invalid.
Aquinas’ Theological Response: Substance Over Accident
St. Thomas Aquinas, with characteristic clarity and charity, addresses this issue directly in his Summa Theologiae, Part III, Question 74, Article 4, asking:
“Whether the matter of this sacrament is bread made of wheat and water?”
And further:
“Whether unleavened or leavened bread is required?”
Aquinas explains:
“It is the substance, not the accident, that pertains to the reality of the sacrament.”
— Summa Theologiae, III, q. 74, a. 4
Key Points from Aquinas:
1. Substance is the matter required, not the accident:
o What is essential is that the bread is true bread, made from wheat flour and water.
o Whether or not it contains leaven is an accidental quality, not essential to the nature of bread.
2. Both are valid, neither is invalid:
o Leavened bread is valid matter for the Eucharist.
o Unleavened bread is equally valid.
o The Church has the authority to choose which is most fitting for her liturgical use.
3. The Latin custom is rooted in Scripture and reverence:
o Christ instituted the Eucharist at the Passover, where unleavened bread was mandated.
o Thus, the Latin practice actually imitates Christ most literally.
4. Liturgical diversity does not imply doctrinal divergence:
o Differences in rite or custom do not undermine the unity of the faith, so long as the essentials are preserved.
o The Church has long recognized the legitimacy of diverse liturgical traditions.

Theological Implications and Ecclesial Authority
For Aquinas, this debate underscores a deeper principle: the Church's authority to regulate the sacramental signs without altering their substantial matter or form.
• The substance of the Eucharist (bread and wine) must be preserved.
• The accidents (e.g., leavened or unleavened, color, texture) may vary based on liturgical tradition.
By maintaining that unleavened bread does not detract from the validity of the sacrament, Aquinas defends both the integrity of Latin sacramental theology and the universality of the Church.
East and West: Shared Essence, Distinct Expression
While the East emphasizes leavened bread to highlight the Resurrection and the living Body of Christ, the West, by using unleavened bread, reflects the Passover roots of the Eucharist and Christ as the unblemished Lamb.
These are complementary emphases not contradictions.
What Aquinas decisively affirms is that neither tradition violates the truth of the sacrament. For both retain the essential matter true bread and the essential form the words of Christ, "This is My Body."
Fidelity Through Diversity
The debate over leavened and unleavened bread illustrates the broader tension between uniformity and universality in the Church.
St. Thomas Aquinas provides a reasoned and reverent response that:
• Defends the validity of Latin sacramental practice.
• Respects the diversity within the Church’s liturgical heritage.
• Maintains the core doctrine of the Eucharist: that Christ becomes truly present in substance, even while the accidents of bread and wine remain.
Thus, the Eucharist remains One Lord, One Faith, One Sacrifice no matter which rite or tradition celebrates it.
A Hopeful Outlook
Despite these differences, Aquinas held out hope for unity. He believed that the Eastern Orthodox errors often came from confusion, not rebellion.
He frequently quoted Eastern Fathers like St. John Chrysostom and St. Basil the Great to defend Catholic doctrines. His desire wasn’t to condemn, but to correct with charity.
Conclusion & Final Thoughts
So what can we take away?
• St. Thomas Aquinas provides a clear, reasoned defense of Latin Catholic doctrine.
• He respects Eastern tradition but calls it to the fullness of truth found in the Church.
• His writings remind us: truth and charity must go hand-in-hand when addressing theological divisions.
Let’s close with a brief prayer.
Prayer:
Heavenly Father, grant us the grace to understand Your truth deeply, to seek unity where possible, and to correct error with love. Through the intercession of St. Thomas Aquinas, may we grow in knowledge and in charity. In the name of the Father, and of the Son, and of the Holy Spirit. Amen.
Thank you for joining us today. If you enjoyed this episode, don’t forget to subscribe and share it with friends. Until next time, stay faithful, stay humble, and stay rooted in tradition.