What is the difference between an encyclical, an apostolic constitution, a papal bull, and a pastoral letter?

Each of these titles has a certain nuance which distinguishes them from each other.  An apostolic constitution represents a very solemn pronouncement issued by the Pope on a doctrinal or disciplinary question.  For example, Pope Paul VI’s apostolic constitution Missale Romanum (1969) promulgated for the whole Church the new missal to be used at Mass.  (A less weighty matter may also be addressed by a motu proprio which is similar to an executive order.)

A papal “bull” is a very dramatic way of presenting such a solemn pronouncement.  Written on parchment, a lead seal (bulla) is attached with cords of silk.  On one side of the seal would be the image of the reigning pope, and the other side would bear the images of St. Peter and St. Paul.  For example, the dogma of the Assumption of our Blessed Mother was issued through the apostolic constitution, Munificentissimus Deus (1950) in the form of a papal bull.  Even the wording indicates the solemn and definitive nature of the teaching:  The document begins, “The Apostolic Constitution by which is defined the dogma of faith that Mary, the Virgin Mother of God, has been assumed into Heaven in Body and Soul, Pius the Bishop, Servant of the Servants of God, for everlasting remembrance.”

Broader in scope and less solemn, an encyclical denotes a pastoral letter written by the Holy Father for the entire Church.  This document focuses on a pastoral issue concerning a matter of doctrine, morality, devotion, or discipline.  Since the earliest days of the Church, Popes have issued this kind of letter.  However, Pope Benedict XIV was the first in modern times to specifically use “an encyclical” with his Ubi primum (1740) which dealt with the duties of bishops.  (Note that the official title of an encyclical is generally the first two or three words of the text’s Latin translation, the official language of issuance.)  Since that time, the Popes have used encyclicals as the normal medium for teaching to the whole Church.  Even the salutation of an encyclical captures the broadness of the audience to which it is addressed.  For example, Pope John Paul II’s recent encyclical The Gospel of Life (1995) begins with the salutation, “John Paul II to the Bishops, Priests, and Deacons, Men and Women Religious, Lay Faithful, and All People of Good Will on the Value and Inviolability of Human Life.”  Sometimes the encyclical may be addressed to a particular audience:  For example another recent encyclical The Splendor of Truth (1993) begins, “Venerable Brothers in the Episcopate, Health and the Apostolic Blessing!” indicating its primary audience as the Bishops throughout the world who in turn will teach the people entrusted to their care.

Although encyclicals are not the normal medium through which the Pope would issue an infallible statement (although he could), the teaching contained in the encyclical represents a part of the ordinary magisterium of the Church held by the Holy Father and therefore commands respect and assent.  The Dogmatic Constitution on the Church of the Second Vatican Council asserted clearly the role of the Pope as the “supreme pastor and teacher of all the faithful” (#25).  Even though the teaching may not be formally declared infallible, Vatican II exhorted that “his supreme teaching authority be acknowledged with respect, and sincere assent be given to decisions made by him, conformably with his manifest mind and intention…” and that “loyal submission of the will and intellect must be given…” to the teaching.

Just as the Pope holds universal teaching authority for the whole Church throughout the world, a bishop may write a pastoral letter to instruct the faithful of his diocese.  Vatican II stated, “[The Bishops] are authentic teachers… endowed with the authority of Christ, who preach the faith to the people assigned to them, the faith which is destined to inform their thinking and direct their conduct” (Dogmatic Constitution on the Church, #25).  Like the encyclical, the subject matter may be doctrinal, moral, devotional, or disciplinary.  For example, Bishop John Keating has written several pastoral letters during his tenure as Bishop of the Diocese of Arlington:  A Pastoral Letter on Morality and Conscience (1994) was more doctrinal, A Pastoral Letter on Parish Councils (1985) was more disciplinary, and A Pastoral Letter on Reverence for the Eucharist (1988) was doctrinal, devotional, and disciplinary.  In turn, the faithful of the diocese are called “to adhere to [the teaching] with a ready and respectful allegiance of mind” (#25).

Several bishops may jointly issue a pastoral letter.  For example, recently the Bishops of the Provinces of Baltimore and Washington issued a pastoral letter during Lent, 1992, encouraging people to utilize the Sacrament of Penance.  The National Conference of Catholic Bishops has also written numerous pastoral letters providing guidance to Catholics throughout the United States.

In all, through these various documents, the Church continues to preserve the faith and to address issues confronting the faithful today so that they can live an authentic Christian life.