What sedevacantism holds
Sedevacantism takes its name from sede vacante ("the see being vacant"), the term normally used for the interval between one pope's death or resignation and the election of the next. Sedevacantists hold that this interval has, in effect, lasted for decades. In the usual formulation, the men elected since the death of Pius XII in 1958 (in some accounts, since the death of John XXIII in 1963) have not been true popes, because adherents consider them to have professed heresy (overview).
The position grew out of the rejection of the theological and disciplinary changes that followed the Second Vatican Council. Adherents commonly point to the liturgical reform, ecumenism and the council's teaching on religious liberty as breaks with earlier teaching. They argue that recognising the post-conciliar popes would imply that the Church itself had erred, which they say the Church's indefectibility rules out.
Sedevacantism differs from the stance of the Society of Saint Pius X, whose magazine The Angelus published critiques of it (see below), and from the "recognise and resist" approach discussed under papal authority. It also differs from benevacantism, which concerns Benedict XVI's resignation rather than the post-conciliar papacy as a whole.
Origins and episcopal lineages
An early public proponent in the United States was Francis Schuckardt. By the late 1960s he had publicly declared Paul VI an antipope and the Holy See vacant. His community, founded in Coeur d'Alene, Idaho, in 1967, is the origin of today's Congregation of Mary Immaculate Queen (CMRI) (Wikipedia; Magnus Lundberg, 2024).
Sedevacantists do not accept bishops appointed by the popes they reject, so their clergy depend on bishops consecrated without a papal mandate. Two lines are especially significant:
- Thục–Carmona. In 1981 Archbishop Ngô Đình Thục consecrated the Mexican priest Moisés Carmona (17 October 1981). Carmona in turn consecrated the Americans George Musey and Mark Pivarunas; Pivarunas was consecrated on 24 September 1991 at Mount Saint Michael in Spokane (Wikipedia: Carmona; Catholic-Hierarchy).
- Thục–Guérard des Lauriers. Thục also consecrated the French Dominican Michel-Louis Guérard des Lauriers in Toulon in May 1981. Guérard des Lauriers later consecrated Günther Storck and Robert McKenna, and McKenna consecrated Donald Sanborn in Detroit on 19 June 2002 (Wikipedia: Guérard des Lauriers; Wikipedia: Sanborn). According to the same encyclopedic account, a 1983 Vatican finding declared that an automatic excommunication applied to Guérard des Lauriers.
Sedeprivationism: the Cassiciacum thesis
Sedeprivationism, also called the Cassiciacum thesis, was developed by Guérard des Lauriers (1898–1988). He had taught at the Society of Saint Pius X seminary at Écône until his appointment there was ended in 1977 over his position on the papacy. The thesis takes its name from the journal Cahiers de Cassiciacum, whose first issue (May 1979) set it out (Wikipedia: Sedeprivationism).
The thesis applies the scholastic distinction between matter and form to the papacy. On this view, a man duly designated to the Roman see holds the papacy materialiter (materially). The post-conciliar claimants are said to lack the formal element, the authority to teach and govern as Christ's vicar, unless they withdraw the changes of Vatican II.
A 2026 critical essay at Nuntiatoria summarises how the thesis relies on an obex, an obstacle in the will, to explain why authority is not received. The essay notes that proponents date the formal vacancy to 7 December 1965 at the latest, linking it to the declaration Dignitatis Humanae. It argues that the thesis does not solve the problem it was designed to address. Commentators disagree on whether sedeprivationism is a form of sedevacantism or a neighbouring position.
Donald Sanborn is known for advocating sedeprivationism. He is rector of Most Holy Trinity Seminary and superior general of the Roman Catholic Institute (Wikipedia).
Institutions, size and reach
Sedevacantism has no central authority. It includes religious congregations, independent chapels, seminaries and, at its margins, "conclavist" groups that have elected their own claimants to the papacy (overview).
- CMRI. The scholar Magnus Lundberg described the CMRI in a 2024 research report as one of the largest sedevacantist groups worldwide. Its motherhouse is at Mount Saint Michael, a former Jesuit property in Spokane, Washington (Lundberg; Wikipedia).
- Most Holy Trinity Seminary. Sanborn founded the seminary in 1995. In 2003 the Tampa Bay Times reported plans to build it in Hernando County, Florida, to train about 18 to 20 priests. The seminary moved from Brooksville, Florida, to Reading, Pennsylvania, in fall 2022 (Wikipedia).
- Movement in both directions. In 2007, fifteen sisters at the CMRI motherhouse who had come to accept the authority of the post-conciliar popes left the congregation. They later formed the Sisters of Mary, Mother of the Church in the Diocese of Spokane (Catholic World Report). In 2026 the Transalpine Redemptorists of Papa Stronsay in Orkney, Scotland, went the other way. They abandoned their earlier reconciliation with the Holy See, and in a May statement declined juridical recognition to Pope Leo XIV (Catholic World Report/CNA).
The sources reviewed for this explainer did not include a reliable count of sedevacantist adherents.
Online presence
Sedevacantist institutions publish online, and some events are livestreamed. The July 2026 consecration on Papa Stronsay, for example, was streamed from the monastery (National Catholic Register/CNA). Mainstream apologetics outlets also respond to sedevacantist arguments. Catholic Answers has published Jimmy Akin's video "The Errors of Sedevacantism" and a video answering a sedevacantist claim that Pope Leo XIV is not a true pope.
Some sedevacantist outlets are primarily online. In April 2025 UnHerd described Novus Ordo Watch as a "meme-posting page" with more than 25,000 followers on X and 13,000 on Facebook, and estimated that there are at most 30,000 sedevacantists worldwide in dozens of organisations (UnHerd). Most Holy Family Monastery in Fillmore, New York, led by the brothers Michael Dimond and Peter Dimond, publishes videos, articles and debates at vaticancatholic.com; the Diocese of Buffalo has said it has no affiliation with the Catholic Church, and the Southern Poverty Law Center lists it as a hate group (Wikipedia; SPLC).
Canonical situation
Sedevacantist clergy and institutions operate outside the Catholic Church's hierarchy. The reference site Catholic-Hierarchy lists Pivarunas as not in union with the Holy See (Catholic-Hierarchy).
The 2026 Papa Stronsay case shows how a diocese responds. On 25 July 2026 the Diocese of Aberdeen said a canonical process had found the community's founder, Fr. Michael Mary (Sim), guilty of schism. It declared him excommunicated, dismissed from ecclesiastical office and barred from celebrating the sacraments. It said the penalties could be lifted after a sincere change of heart and reparation (LifeSiteNews; CathNews).
In the Philippines, CBCP News reported a bishop warning the faithful against a local sedevacantist group whose members deny the validity of the Catholic Church's sacraments (CBCP News).
What the Church teaches on the points at issue
- The succession of Peter. Lumen Gentium teaches that the office Christ entrusted to Peter is permanent and passes to his successors (LG 20). It teaches that the Roman Pontiff has full, supreme and universal power over the Church (LG 22) and is the perpetual and visible source and foundation of unity of bishops and faithful (LG 23) (Lumen Gentium).
- Unity and schism. The Catechism names heresy, apostasy and schism as ruptures that wound the unity of Christ's Body (CCC 817). It teaches that particular Churches are fully catholic through communion with the Church of Rome (CCC 834) (Catechism).
- Arguments from within traditionalism. The traditionalist writer Michael Davies, writing in the SSPX-linked Angelus in 1983, argued that sedevacantism's central difficulty is explaining how the Church can remain visible without a head (The Angelus, 1983). Catholic Answers' Jimmy Akin argues that the reasons sedevacantists give are faulty and contrary to Christ's promises (Catholic Answers).
Key outlets and voices
- Congregation of Mary Immaculate Queen (CMRI), led by Bishop Mark Pivarunas
- Most Holy Trinity Seminary, led by Bishop Donald Sanborn
- Michel-Louis Guérard des Lauriers, author of the Cassiciacum thesis (historical)
- Most Holy Family Monastery (vaticancatholic.com), led by Michael Dimond and Peter Dimond
- Novus Ordo Watch, sedevacantist website and TRADCAST podcast
- Related: Feeneyism, Extra ecclesiam nulla salus, Validity of the Novus Ordo, Vatican II and its authority