Growing reference · adhered to in every lesson · added to as we go
Era
One of the four great divisions of church history: Early, Medieval, Reformation, Modern.
Ecumenical Council
A church-wide gathering of bishops to settle doctrine (e.g. Nicaea 325, Chalcedon 451).
Trinity
The doctrine that God is one being in three persons — Father, Son, Spirit. Defined in the Early Church. Formula: one ousia, three hypostaseis — one "what," three "whos."
Ousia (οὐσία) · oo-SEE-ah
(Greek: "being, essence") Answers "What is God?" — the one divine essence/substance shared fully by all three persons. God is one of these. Latin: essentia (es-SEN-tee-ah) / substantia (sub-STAN-tee-ah).
Hypostasis (ὑπόστασις) · hoo-POSS-ta-sis
(Greek: lit. "what stands under") Answers "Who is God?" — a distinct, concrete person. God is three of these (pl. hypostaseis, hoo-po-STA-sees). Latin: persona. (Originally a near-synonym of ousia, which caused decades of confusion.)
Persona / Prosopon · per-SOH-nah / PROSS-oh-pon
Latin/Greek for "person." Both originally meant a theatrical mask/role — a sense modalists exploited — until anchored to hypostasis to mean a real, distinct "who."
Cappadocian Fathers
Basil of Caesarea, Gregory of Nyssa, and Gregory of Nazianzus (~360–380), who fixed the Trinity's vocabulary (hypostasis = three, ousia = one) and made the Council of Constantinople (381) possible.
Council of Constantinople (381)
The second ecumenical council; completed the Nicene Creed, affirmed the deity of the Holy Spirit, and finally settled the Arian controversy.
Physis (φύσις) · FOO-sis
(Greek: "nature") The kind of thing something is. Jesus has two — divine and human — united in one person.
Council of Ephesus (431) · EFF-eh-sus
The third ecumenical council. Affirmed that Christ is one person (against Nestorianism) and that Mary is rightly called Theotokos. Sits between Constantinople (381) and Chalcedon (451) in the council chain; its rejected party became the Church of the East.
Council of Chalcedon (451)
The fourth ecumenical council. Defined Christ as one person in two natures, "without confusion, without change, without division, without separation." Capstone of the "Who is Jesus?" question.
Nestorianism
The error that so separates Christ's two natures they become almost two persons. Refused Mary the title Theotokos. Condemned (Ephesus 431; Chalcedon 451).
The opposite error: Christ has only one nature, his humanity swallowed by his divinity (mono = one, physis = nature). Condemned at Chalcedon.
Theotokos (Θεοτόκος) · theh-oh-TOH-kos
(Greek: "God-bearer") Title affirming that the one Mary bore truly is God the Son — a statement about Christ's unity, not mainly about Mary.
Oriental Orthodox
Churches (Coptic, Armenian, Ethiopian, Syriac) that rejected Chalcedon's "two natures" language and broke away — Christianity's first major lasting division (451).
Arianism
The 4th-c. teaching (from Arius, a priest of Alexandria) that Jesus was a created being — the highest creature, but not eternal or fully God. Rejected at Nicaea. Slogan: "there was when he was not."
Subordinationism
The tendency to rank the Son (and Spirit) as lesser than the Father. A loose strand in some early writers that Arius sharpened into full Arianism. Traced: Paul of Samosata → Lucian of Antioch ("the Arius before Arius") → Arius.
Modalism (Sabellianism)
The opposite error to Arianism: God is one person appearing in three modes/masks (Father, Son, Spirit), not three distinct persons. Named for Sabellius. Forerunners: Noetus, Praxeas. Condemned.
Monarchianism
Umbrella term for attempts to protect God's "sole rule"/oneness — including Modalism. Over-guards unity at the expense of the three persons.
Patripassianism
(Latin: "the Father suffered") Tertullian's mocking label for Modalism: if the Father is the Son, then the Father died on the cross.
Ante-Nicene Fathers
Christian writers before the Council of Nicaea (325) — e.g. Ignatius, Irenaeus, Tertullian — key witnesses to what the early church believed.
Homoousios
(Greek: "of the same substance") The decisive word of the Nicene Creed: the Son is of the very same being as the Father — fully God, not a creature.
Nicene Creed
The statement of faith produced at Nicaea (325, expanded 381) affirming the full deity of Christ ("begotten, not made… true God from true God"); still recited in churches worldwide.
Athanasius
Bishop of Alexandria whose lifelong defense of Christ's full deity secured Nicene orthodoxy against Arianism.
Heresy / Orthodoxy
Orthodoxy = right/accepted teaching; heresy = a teaching the church judged to be a serious departure from it (e.g. Arianism).
Monasticism
(from Greek monos · MOH-nos, "alone") Movement of Christians withdrawing for prayer, discipline, and community; begins in the Early Church (desert hermits) and becomes the backbone of the Medieval West. Engine of preservation: copied books, farmed, evangelized, ran schools and hospitals. Marked by a recurring rhythm of drift into wealth → reform → drift again.
Antony of Egypt (~270) · AN-toh-nee
The famous early hermit who withdrew to the Egyptian desert to seek God alone — the root figure of monasticism. Pachomius (pa-KOH-mee-us) then built the first shared (communal) monastery.
Benedict of Nursia (~530) · BEN-eh-dikt · NUR-see-ah
Father of Western monasticism. At Monte Cassino he wrote the Rule of St. Benedict, a short, humane handbook (motto ora et labora, "pray and work") that became the standard pattern for Western monasteries for ~1,000 years.
Ora et labora · OH-rah et lah-BOR-ah
(Latin: "pray and work") The Benedictine motto — a daily balance of worship, study, and manual labor.
Scriptorium · skrip-TOR-ee-um
The room in a monastery where monks hand-copied books. Much of the Bible and the classical writings of antiquity survived the fall of Rome because a monk copied them here.
Cluniac reform (from 910) · KLOO-nee-ak
The reform movement launched from the abbey of Cluny in France to cleanse corrupt, worldly monasteries — disciplined, prayer-centred, free of political control. (The later Cistercians under Bernard of Clairvaux reformed again.) Fed the wider reforming spirit behind Gregory VII.
"Dark Ages" (Early Middle Ages, ~500–1000)
A contested nickname for the first half of the Medieval era — not the whole of it. Coined by later (Renaissance/Enlightenment) writers for the period after Rome fell (476), when Western cities, trade, government, and literacy collapsed ("dark" = decline) and few records survive ("dark" = we can't see). Most historians now avoid the term as a misleading sneer: the monasteries (esp. the scriptorium) kept faith and learning alive the whole time. Followed by the High (~1000–1300) and Late (~1300–1500) Middle Ages.
Papacy
The office and authority of the Bishop of Rome (the Pope); rises to prominence in the Medieval era. Climbed in stages: honored "first among equals" (2nd–3rd c.) → claim to supremacy (Leo I, ~450) → governing (Gregory I, ~600) → over kings (Gregory VII, 1077). Engine of the climb: the power vacuum left by the fallen Western Empire (476).
Leo I "the Great" (440–461)
The first Pope to clearly claim that the Bishop of Rome inherits Peter's authority over the whole church (Petrine supremacy). His Tome shaped the Definition of Chalcedon (451); legend says he turned Attila the Hun back from Rome (452).
Gregory I "the Great" (590–604)
Generally regarded as the first medieval pope. With no emperor left in the West, he governed Rome, fed its people, and sent missionaries (Augustine of Canterbury to England, 597). Made the Pope a ruler and missionary strategist, not just a bishop.
Investiture Controversy / Canossa · kah-NOSS-ah
The 11th-c. clash over who appoints (invests) bishops — Pope vs. Emperor. Gregory VII (Hildebrand) excommunicated Emperor Henry IV, who in 1077 begged forgiveness barefoot in the snow at Canossa. High-water mark of papal claims over kings.
Donation of Constantine
A forged document claiming Emperor Constantine gave the Pope authority over the Western empire; long used to bolster papal power, exposed as a fake by Lorenzo Valla in 1440. A classic case of honest history checking its sources.
Great Schism (1054)
The split between the Eastern (Orthodox) and Western (Roman Catholic) churches. Driven by two engines — the filioque (a word added to the creed) and the papacy (one Pope's claim to rule all). Sealed when papal legates and Patriarch Michael Cerularius excommunicated each other in Hagia Sophia. The symbolic date; the true rupture deepened in 1204 (sack of Constantinople).
Filioque (Latin) · fih-lee-OH-kweh
(Latin: "and the Son") The Western addition to the Nicene Creed: the Holy Spirit proceeds "from the Father and the Son" (vs. the original "from the Father"). The East objected both to the theology and to the West changing the universal creed without an ecumenical council. A central cause of the 1054 schism.
Eastern Orthodox
The Greek-speaking Eastern church, centred on Constantinople; governed by patriarchs as equals rather than one head. Kept the creed unchanged (no filioque). Today: Greek, Russian, Serbian Orthodox, etc. One of the two families produced by the 1054 schism.
Roman Catholic
The Latin-speaking Western church, centred on Rome under the Pope. Added the filioque; held the Pope as supreme head. The other family of the 1054 schism — and the church the Protestant Reformation later split from (1517).
Patriarch / Pentarchy · PEN-tar-kee
A patriarch is a leading bishop of a major ancient see. The pentarchy = the five great sees (Rome, Constantinople, Antioch, Alexandria, Jerusalem) sharing authority. The East saw Rome as "first among equals"; the West saw Rome as supreme — a core dispute behind 1054.
The ~70 years when seven popes in a row ruled from Avignon in France rather than Rome — widely seen as puppets of the French crown. Critics dubbed it the church's "Babylonian Captivity" (after Israel's exile). First great crack in late-medieval papal authority.
Great Western Schism (1378–1417) · SKIZ-um
The crisis of two (then three) rival popes, each claiming to be the true one and excommunicating the others, splitting Western Christendom for ~40 years. Not the 1054 East–West Great Schism — this one is Catholics vs. Catholics. Did more than anything to discredit the papacy before the Reformation.
Council of Constance / conciliarism (1414–1418) · KON-stanss · kon-SIL-ee-ar-izm
The council that ended the Western Schism by removing all claimants and electing one pope (Martin V, 1417) — and that also condemned and burned Jan Hus. To act it assumed conciliarism: that a general council outranks the pope. The fix worked, but left the "where does authority sit?" question open.
John Wycliffe / Lollards (d. 1384) · WIK-liff · LOL-erdz
Oxford scholar called "the Morning Star of the Reformation": argued the Bible (not the pope) is the final authority, attacked church wealth, questioned transubstantiation, and pushed the Bible into English. His followers were the Lollards. A medieval Catholic reformer — not yet a Protestant — but voicing Luther's themes ~130 years early.
Jan Hus (d. 1415) · YAHN HUSS
Bohemian (Czech) preacher who took up Wycliffe's ideas; summoned to the Council of Constance under a safe-conduct, then burned at the stake anyway (1415). Became a martyr and national hero. Luther later read him and said, "we are all Hussites." The second "morning star."
"Morning stars of the Reformation"
Nickname (hindsight) for the reformers — chiefly Wycliffe and Hus — who anticipated the Reformation's core complaints (Scripture over pope, reform of corrupt clergy) a century before Luther. The stars that rise just before dawn. Useful, but don't flatten their real differences from Luther.
Scholasticism
Medieval method of theology using rigorous logic/philosophy (e.g. Thomas Aquinas).
Reformation
The 16th-c. movement (from Luther, 1517) to reform the Western church; birth of Protestantism.
Protestant
Christian traditions stemming from the Reformation, marked by Scripture alone, grace alone, faith alone.
Martin Luther (1483–1546)
The Augustinian monk whose search for a gracious God sparked the Reformation. Found in Romans that righteousness is a gift received by faith, not earned; posted the 95 Theses (1517); refused to recant at the Diet of Worms (1521). A mixed figure — courageous reformer, but also author of late, ugly anti-Jewish writings.
Justification by faith
Luther's central rediscovery: a sinner is declared right with God as a gift received by trusting Christ, not earned by works, penance, or payments. The engine of the Reformation; captured in the slogan sola fide.
Indulgence / Tetzel · in-DUL-jens · TET-sel
An indulgence was a church grant said to lessen punishment for sin. The aggressive sale of indulgences (to fund St. Peter's Basilica) by the friar Tetzel — "when a coin in the coffer rings, a soul from purgatory springs" — was the abuse that provoked Luther's 95 Theses.
95 Theses (Oct 31, 1517)
Luther's 95 short points for academic debate, attacking the sale of indulgences, posted/sent at Wittenberg (VIT-en-berg). Meant as scholarly argument, not revolution — but the printing press spread them across Germany in weeks, igniting the Reformation. (The dramatic door-nailing is partly later tradition.)
Diet of Worms (1521) · DEET of VORMS
The imperial assembly where Luther was ordered to recant and refused — unless proven wrong by Scripture, his conscience was "captive to the Word of God." Traditionally: "Here I stand, I can do no other." He was excommunicated; the break with Rome became permanent. (A "diet" = a formal assembly.)
The "solas" · SOH-lah
Latin rallying cries of the Reformation, each beginning sola ("alone"): sola fide (FEE-deh, faith alone), sola scriptura (skrip-TOO-rah, Scripture alone — the Bible, not pope or council, is the final authority), and sola gratia (GRAH-tee-ah, grace alone). (Later lists add solus Christus and soli Deo gloria.)
Reformed tradition
The Protestant family flowing from Zwingli and especially Calvin — emphasizing God's sovereignty, predestination, Scripture ordering all of life, simpler worship, and Presbyterian (elder-led) church government. Heirs: Presbyterian, Reformed, Congregational churches; the Puritans; Knox's Scotland; the Dutch Reformed.
Reformer of Zürich (ZUR-ik), a parallel pioneer to Luther and founder of the Reformed stream. Held the Lord's Supper to be a symbol/memorial — the point on which he and Luther split at the Marburg Colloquy (1529).
John Calvin (1509–1564) / Institutes
The great systematizer of the Reformation, based in Geneva. His Institutes of the Christian Religion gave Protestantism its most thorough theological system (God's sovereignty, predestination, Scripture's rule over all of life). Shaped the Reformed/Presbyterian world more than any other thinker after Luther.
The "radicals" who said Luther and Calvin didn't go far enough: baptism is for believing adults, not infants (ana- = "again," they re-baptized), the church should be separate from the state and made only of committed disciples, often pacifist. Persecuted by Catholics and Protestants. Heirs: Mennonites, Amish, Hutterites; a root of the Baptists.
Anglican / via media · ANG-lih-kan · VEE-ah MEE-dee-ah
England's branch, born politically when Henry VIII made himself head of the Church of England (1534) after Rome refused him a divorce. Settled into a deliberate "middle way" — Protestant in doctrine, Catholic in much of its worship. Heirs: the Anglican Communion, Episcopalians, later the Methodists.
Marburg Colloquy (1529) · MAR-boorg
The meeting where Luther and Zwingli tried to unite the Reformation — and broke over a single question: how is Christ present in the Lord's Supper? (real presence vs. symbol). The first major Protestant-vs-Protestant divide.
Counter-Reformation / Catholic Reformation
Rome's powerful 16th-c. response to the Reformation, in three moves: define (the Council of Trent), renew (new orders like the Jesuits, and mystics), defend (the Inquisition and Index). Part reaction to Protestantism, part genuine renewal that had begun before Luther — hence the two names. Reshaped the world map of Christianity (Protestant north, Catholic south, global Catholic missions).
Council of Trent (1545–1563) · TRENT
The council that answered the Reformation point by point: affirmed Scripture and tradition, faith and works, all seven sacraments, and transubstantiation (rejecting the Protestant solas) — and reformed real abuses (banned indulgence-selling, required resident bishops, founded seminaries). Defined Catholic doctrine essentially until the 1960s (Vatican II). The "both/and" to the reformers' "alone."
The Society of Jesus (founded 1540 by the soldier-turned-saint Ignatius of Loyola): a disciplined, highly educated order loyal to the pope, who became Catholicism's great teachers and missionaries (e.g. Francis Xavier to India and Japan). A spearhead of the Counter-Reformation.
Teresa of Ávila (1515–1582) · teh-REH-sah · AH-vee-lah
Spanish nun, mystic, and reformer of the Carmelite order; renewed Catholic prayer and devotion from within during the Counter-Reformation. A reminder that Rome's revival was spiritual, not only institutional. Later named a Doctor of the Church.
Mysticism (Christian) · MISS-tih-sizm
Not the occult/New Age sense the modern word suggests. In church history it means the pursuit of a direct, experiential union with God through deep prayer and contemplation — knowing God as encountered, not just studied. The church honored it when tethered to Scripture, doctrine, humility, and obedience (e.g. Teresa of Ávila, medieval mystics like Bernard of Clairvaux); it condemned it when mystics claimed experiences that overrode doctrine or church authority (e.g. the Spanish alumbrados, ah-loom-BRAH-dohs). The risk: a "direct line to God" can seem to bypass church, sacrament, and Scripture. Protestants are often wary for the same reason, yet have their own contemplative streams.
Roman Inquisition / Index of Forbidden Books · in-kwih-ZISH-un
The coercive edge of the Counter-Reformation: the Inquisition (courts to hunt and suppress heresy) and the Index (an official list of books Catholics were forbidden to read — including, for a time, Protestant works and Bibles). The repression that came alongside the genuine renewal.
Revivalism
Modern-era movements of intense renewal and conversion (e.g. the Great Awakenings).