The Vatican announced on May 9 a decree from Pope Francis related to bishop accountability and child protection. The decree, “Vos Estis Lux Mundi,” was issued motu proprio. This new law joins many others promulgated by Pope Francis, including “Magnum Principium,” which involved the fraught issue of liturgical translations, for which the pope shifted the responsibility back to national bishops’ conferences, as well as “Summa Familiae Cura,” which rebooted a Rome-based academic institute established by Pope John Paul II to study family life, in order to incorporate some of Francis’ teachings on the subject.

In all three instances, the pope’s teachings were issued motu proprio, a detail reported by Catholic journalists to underscore the significance of both moves. The Latin phrase certainly sounds weighty—and it is—but more than a few Catholics were left wondering what, exactly, it means.

When a pope issues a document motu proprio, it means he does so by his own motivation. As Catholic News Service puts in its style guide, “Popes use it to signal a special personal interest in the subject.” The phrase motu proprio does not refer to a document itself, but rather the manner in which a document is released. That is, a document is released motu proprio when the pope wants to change or enact an existing church rule—or when he has something to say that is not in reply to a request or a petition but instead comes from his own interest in a particular matter.

A document is released motu proprio when the pope has something to say that is not in reply to a request but instead comes from his own interest in a particular matter.

There is a governing element to statements released motu proprio.

In the Catholic Church, the pope serves as both executive and legislator. What he says, goes. But how he says something indicates how far it will go. When he issues documents motu proprio, he acts in his capacity as legislator, meaning, for example, that he is updating canon law or making other changes that amount to a legislative act. Legislative changes made by a pope overrule decisions by other Vatican departments, so even small changes to church law resulting from documents issued motu proprio can be significant.

Take the rise of the Latin Mass—and the return of the liturgy wars—over the past decade. Pope Benedict XVI altered rules from 1970 that limited the Latin Mass by releasing “Summorum Pontificum,” an apostolic letter that he issued motu proprio in 2007. That statement altered church law by waiving a requirement that priests who wish to celebrate the Latin Mass obtain special permission from church authorities; critics say that removing the requirement was a rollback of reforms from the Second Vatican Council..

According to the Vatican website, Pope John Paul II issued 31 documents motu proprio; Pope Benedict XVI, 13; and Pope Francis, so far, 29.

Sometimes, a pope will act in a legislative manner, but the changes will be more sweeping than small modifications of church law. In these cases, the document is not issued motu proprio but is instead called an apostolic constitution.

For example, when Pope Francis mandated changes in the prayer lives of cloistered Catholic nuns in 2016, changes that would affect communities all over the world, he issued an apostolic constitution called “Vultum Dei Quaerere.” Pope John Paul II released an apostolic constitution, “Ex Corde Ecclesiae,” which was meant to bolster the Catholic identities of colleges and universities affiliated with the church. A document released motu proprio might clarify or modify an apostolic constitution.

There are also other forms of papal teaching, including encyclicals and apostolic exhortations, that come from the pope and are considered part of the church’s teaching, but they do not necessarily concern church law. They can, however, have great impact on the Catholic Church: The ongoing debate about whether divorced and remarried Catholics should be admitted to Communion owes its genesis not to a change in law, but to “Amoris Laetitia,” an apostolic exhortation.

Editor’s note: This article was updated May 9, 2019, with information about “Vos Estis Lux Mundi.”

Michael J. O’Loughlin is national correspondent at America and author of Hidden Mercy: AIDS, Catholics, and the Untold Stories of Compassion in the Face of Fear.