The 21 Ecumenical Councils: Codifying What Was Always Believed

A Comprehensive Guide Showing That Councils Define, They Don't Invent

For Catholic Adult Faith Formation


Key Principle

Councils are REACTIVE, not CREATIVE

Every ecumenical council was convened to address a specific heresy or crisis. The council's definition codifies what the Church has always believed, giving it formal, dogmatic status. The doctrine existed before the definition—the council simply makes explicit what was implicit.

St. Vincent of Lérins (434 AD): "We hold that faith which has been believed everywhere, always, by all."


THE 21 ECUMENICAL COUNCILS

1. NICAEA I (325 AD)

The Crisis: Arianism - Arius taught that Jesus was a created being, not truly God

What Was Defined:

When This Was First Believed:

The Point: Nicaea didn't invent the divinity of Christ. It codified 300 years of apostolic teaching against a NEW heresy.


2. CONSTANTINOPLE I (381 AD)

The Crisis:

What Was Defined:

When This Was First Believed:

The Point: The Spirit's divinity was believed from apostolic times. The council formalized it when challenged.


3. EPHESUS (431 AD)

The Crisis: Nestorianism - Nestorius taught Mary was only mother of Christ's human nature, not mother of God. This effectively divided Christ into two persons.

What Was Defined:

When This Was First Believed:

The Point: "Mother of God" was standard Christian language 200+ years before Ephesus. Council defended it against innovation.


4. CHALCEDON (451 AD)

The Crisis:

What Was Defined:

When This Was First Believed:

The Point: Chalcedon's formula summarized 400 years of Christological reflection against a new error.


5. CONSTANTINOPLE II (553 AD)

The Crisis:

What Was Defined:

When Perpetual Virginity Was First Believed:

The Point: Perpetual virginity was universal belief for 400 years before formal definition.


6. CONSTANTINOPLE III (680-681 AD)

The Crisis: Monothelitism - taught Christ had only one will (divine), not both divine and human wills

What Was Defined:

When This Was First Believed:

The Point: The council defended what Scripture and tradition taught against imperial heresy.


7. NICAEA II (787 AD)

The Crisis: Iconoclasm - Emperor Leo III and others condemned use of religious images as idolatry

What Was Defined:

When This Was First Believed:

The Point: Christian images existed from the beginning. Council defended 700 years of practice.


8. CONSTANTINOPLE IV (869-870 AD)

The Crisis:

What Was Defined:

When This Was First Believed:

The Point: Papal authority was recognized from earliest centuries, though its exact parameters developed.


9. LATERAN I (1123 AD)

The Crisis:

What Was Defined:

When Celibacy Was First Practiced:

The Point: Council ended secular interference in spiritual matters, defending Church independence.


10. LATERAN II (1139 AD)

The Crisis:

What Was Defined:

When This Was First Taught:


11. LATERAN III (1179 AD)

The Crisis:

What Was Defined:

When Papal Election Was First Established:


12. LATERAN IV (1215 AD)

The Crisis:

What Was Defined:

When Transubstantiation Was First Believed:

The Point: Council gave philosophical precision to what had ALWAYS been believed.


13. LYONS I (1245 AD)

The Crisis:

What Was Defined:


14. LYONS II (1274 AD)

The Crisis:

What Was Defined:

When Filioque Was First Believed:

When Purgatory Was First Believed:

The Point: Council formally defined what had been believed and practiced for over 1,000 years.


15. VIENNE (1311-1312 AD)

The Crisis:

What Was Defined:

When Soul-Body Unity Was First Believed:


16. CONSTANCE (1414-1418 AD)

The Crisis:

What Was Defined:

When These Doctrines Were First Believed:


17. FLORENCE (1438-1445 AD)

The Crisis:

What Was Defined:

When Seven Sacraments Was First Believed:

Individual Sacrament Origins:

The Point: The number seven was formally defined in medieval period, but each sacrament existed from apostolic times.


18. LATERAN V (1512-1517 AD)

The Crisis:

What Was Defined:

When Immortality of Soul Was First Believed:


19. TRENT (1545-1563 AD)

The Crisis: The Protestant Reformation - challenged almost every Catholic doctrine

What Was Defined: This was the most comprehensive doctrinal council since the early Church. Major definitions:

ON SCRIPTURE & TRADITION:

When This Was First Believed:

ON JUSTIFICATION (1547):

When This Was First Believed:

ON SACRAMENTS (1547-1563):

When Ex Opere Operato Was First Believed:

ON EUCHARIST (1551):

When This Was First Believed:

ON PENANCE/CONFESSION (1551):

When This Was First Believed:

ON MATRIMONY (1563):

When This Was First Believed:

ON HOLY ORDERS (1563):

When This Was First Believed:

ON PURGATORY (1563):

When This Was First Believed:

ON INDULGENCES (1563):

When This Was First Believed:

SUMMARY OF TRENT:

The Point: Trent codified what had ALWAYS been believed against Protestant innovations.


20. VATICAN I (1869-1870 AD)

The Crisis:

What Was Defined:

When Papal Infallibility Was First Believed:

The Point: The doctrine existed; the council gave it formal definition. The WORD "infallibility" was recent, the REALITY was ancient.


21. VATICAN II (1962-1965 AD)

The Crisis:

What Was Defined: IMPORTANT NOTE: Vatican II was primarily pastoral, not dogmatic. It defined NO NEW DOGMAS. It clarified, updated, and applied existing doctrine to modern circumstances.

Major Documents:

Lumen Gentium (On the Church):

Dei Verbum (On Divine Revelation):

Sacrosanctum Concilium (On Sacred Liturgy):

Gaudium et Spes (On Church in Modern World):

Unitatis Redintegratio (On Ecumenism):

Nostra Aetate (On Non-Christian Religions):

Dignitatis Humanae (On Religious Freedom):

Presbyterorum Ordinis, Optatam Totius (On Priesthood):

KEY POINT ABOUT VATICAN II:

When These Teachings Were First Believed: All Vatican II teachings flow from previous councils and Scripture. The council:


PATTERNS ACROSS ALL 21 COUNCILS

1. Councils are REACTIVE

Every council responds to a crisis: heresy, schism, or corruption

2. Councils DEFEND, they don't INVENT

Each doctrine defined had deep roots in Scripture and Tradition

3. Heresies are usually INNOVATIONS

4. Development is ORGANIC, not INVENTIVE

5. Time Gap Between Practice and Definition

Often centuries pass between when something is believed/practiced and when it's formally defined:

6. Crisis Forces Clarity

Heresy forces Church to be explicit about what was previously implicit:


THE KEY INSIGHT

WRONG VIEW: "The Church makes up doctrines at councils to maintain power"

CORRECT VIEW: "The Church codifies at councils what has always been believed, when heretics challenge it"

St. Vincent of Lérins (434 AD): "What is development and what is change?... Development means that each thing expands to be itself, while alteration means that a thing is changed from one thing into another."

John Henry Newman (1845): "Here below to live is to change, and to be perfect is to have changed often" - BUT the development is organic, not contradictory

Example:

Councils ensure DEVELOPMENT, not ALTERATION


TIMELINE VISUALIZATION

30-100 AD: Apostolic teaching - ALL core doctrines present implicitly

100-300 AD: Church Fathers elaborate, defend, hand on

300-800 AD: First seven councils define Christology, Trinity, images

1100-1500 AD: Medieval councils define sacramental theology, refine practices

1545-1563 AD: Trent codifies ALL major doctrines against Protestant revolution

1869-1870 AD: Vatican I defines papal authority explicitly

1962-1965 AD: Vatican II applies ancient truths to modern world


CONCLUSION: COUNCILS CONFIRM, NOT CREATE

Every Council:

The Church's role:

2 Timothy 1:14: "Guard the good deposit entrusted to you"

Jude 3: "Contend for the faith that was once for all delivered to the saints"


For Catholic Adult Faith Formation November 2025