To clarify Pope John Paul II's position on stem-cell research, the Vatican quoted from his 1995 encyclical, Evangelium Vitae. What's an encyclical, and how does it differ from a papal bull?
The Catholic Church articulates and develops its teachings primarily through encyclicals. Traditionally, an encyclical is a letter from the pope to the church's bishops, but during the past 40 years the pope has also addressed them to the faithful and to "all people of good will." Pope John Paul II has issued 13 encyclicals, the latest being 1998's Fides Et Ratio ("Faith and Reason"). Notable encyclicals include Paul VI's 1968 Humanae Vitae ("On Human Life"), which affirmed the church's stance against contraception, and John Paul II's 1995 Evangelium Vitae ("The Gospel of Life"), which condemned the "culture of death" the pope saw manifested in abortion, euthanasia, and capital punishment. The first encyclical was circulated by Benedict XIV in 1740.
Prior to the 18th century, the church expressed its teachings through apostolic bulls, more legalistic and solemn documents than encyclicals. ("Bull" refers to the Latin bulla, or seal, which is affixed to the document.) The condemnation of Martin Luther, for example, came in a papal bull. Today, the Vatican issues bulls mostly to confer the titles of bishops and cardinals or to proclaim the canonization of a saint.
Encyclicals are authoritative, not to be criticized or rejected lightly by members of the church, but they are not infallible. Only three doctrines developed in the past 200 years are considered infallible, and all were issued as bulls: the Immaculate Conception (that Mary was born without original sin), the Assumption (that Mary was taken up body and soul into heaven), and the definition of papal infallibility issued by the First Vatican Council.
Explainer thanks the Rev. John Langan, S.J., of Georgetown University and the Catholic Word Book.