For a brief primer on the authority of church documents, please see Helen Hitchcock's primer at this link: http://www.adoremus.org/0902AuthorityChurchDoc.html
Papal addresses and documents fall into certain recognized categories with levels of authority relative to each other. Below is a description of the major types of Papal documents, with those of higher weight near the top of the list. More details on some of these documents may be found in the New Catholic Encyclopedia.
- Papal Bull
A bull is a formal papal document authenticated with a bulla or seal. Originally, metal was used for the seal, but today metal is used only for the most solemn bulls. Bulls typically begin with the issuing pope's name and the phrase, "episcopus servus servorum Dei", and conclude with the date. The content may cover any topic. Many important papal documents are issued as bulls. Bulls are generally cited using the first words of their text.
- Apostolic Constitution
Apostolic constitutions are the most solemn form of legal document issued by the pope in his own name. Frequently issued as bulls, they deal primarily with serious doctrinal matters. Since 1911 they have also been used for the establishment of dioceses and provinces. Many important documents have been promulgated as constitutions, including The Code of Canon Law.
- Motu Proprio
Motu proprios are legislative, apostolic letters written and signed by the pope on his own initiative. Originally used to settle the affairs of the Curia and administer the Papal States, they now handle legislative matters which are significant but do not merit a constitution. Motu proprios are generally brief, and handle specific issues relevant to the Church in a specific time in history. In recent years they have been one of the principal sources of new laws outside of the Code.
- Encyclical Letter
Encyclicals are papal letters of a pastoral nature, used in their current form since 1740. These letters offer counsel and shed light on existing doctrine as part of the Holy Father's ordinary teaching authority. They do not belong formally to the deposit of revelation, and their teachings are not definitive unless specifically stated as such. Therefore, certain points of their teachings can often be changed.
- Apostolic Epistle or Letter
When an encyclical is written in response to a particular need, or when it is addressed to a specific group of persons, it is called an apostolic epistle. These epistles, pastoral in nature and primarily discussing social concerns, are not considered legislative documents.
- Apostolic Exhortation
Apostolic exhortations are papal reflections on a particular topic which are addressed to all of the clergy and faithful. The form was first used by Pope Pius XII in 1939. Exhortations generally encourage a particular virtue or mission, and are given on specific occasions. They do not contain dogmatic definitions or policies, and they are not considered legislative documents.
- Decretal Letter
Decretals, first used in the 2nd century, originally contained papal decisions related to questions of discipline and administration. During the Middle Ages they were often issued in the form of bulls. In modern times, they are reserved for solemn matters such as dogmatic definitions and canonizations. It is generally accepted that decretals belong to the extraordinary magisterium of the Holy Father; however, they are not considered legislative documents.
- Allocutiones / Addresses
Prior to the 19th century, the term "allocutiones" was generally reserved for solemn addresses given by the Holy Father to his cardinals. Today, however, a variety of less-formal papal allocutions and addresses are published in the Acta Apostolicae Sedis and other sources. Their content is not necessarily tied to the Church or liturgy, but attempts to address specific issues or circumstances and is aimed at particular groups of people.
- Papal Rescript
A papal rescript generally answers a petition placed before one of the Roman Curiae or the Holy Father himself. It is signed by the cardinal prefect and the secretary of the relevant congregation, and also bears that congregation's seal.
- Apostolic Brief
Apostolic briefs, also called brevia, are a simple form of document dealing with matters of relatively-minor importance. This form emerged during the reign of Pope Martin V (1417-31) as a replacement for the ancient form of litterae.