An encyclical, or encyclical letter (Latin: "littera encyclica"), as the term is used in the modern Catholic Church, is a pastoral letter from the Pope and is usually addressed to the whole Church through the Church hierarchy. It may, however, be addressed only to a section of the Church (in which case it is called an encyclical epistle), or directly to the entire people of the Church, or even, on occasion, to the whole world (see, e.g., Pacem in Terris).
The encyclical is an expression of Church teaching (the magisterium, as it is called) on doctrine, faith, morals, discipline or some other important matter. Encyclicals are written in Latin and are generally referred to by the first Latin words of the document.
Pope Sixtus V, in the Papal Bull Immersa aeterni, issued January 22, 1587, organized the offices of the Holy See and at that time the Pontifical documents, including what are now known as Encyclical Letters, were given new names and precisely defined.
Under Catholic doctrine, an Encyclical Letter is an expression of the Church's magisterium or teaching authority, held to derive ultimately from Jesus Christ through his establishment of the Church with the Apostle Peter as its head and continued to the present day via the doctrine of Petrine succession. This teaching authority is held by Catholics to take different forms as defined by official Catholic sources.
The first Vatican Council of 1870 promulgated what has become known as the doctrine of papal infallibility when issuing decrees ex cathedra on matters touching faith or morals. This aspect of Papal utterances is held to be present only on such matters and only when the Pope himself states that he is speaking in virtue of his full authority. The Catholic Church then holds that he is protected by God Himself from error under these conditions.
The doctrine is more fully explicated in the canons of the Vatican Council of 1870 in the document entitled "On the Perpetuity of the Primacy of the Blessed Peter in the Roman Pontiffs":
When issuing encyclicals, it is generally held that the pope does not normally speak with the full power of his authority and thus his utterances are not considered infallible under that doctrine. Even so, Catholic scholars and theologians consider that the pope's words in encyclicals should be received with very great respect, some asserting that they merit at least an internal assent.
The most direct Papal statement on the subject of the authority of Papal Encyclicals is contained in the Encyclical Letter Humani Generis, issued by Pope Pius XII in 1950 where it was held that even when not speaking ex cathedra and thus asserting Papal infallibility, the statements of the Pope as contained in Encyclicals are nevertheless sufficiently authoritative to end theological discussion:
The Second Vatican Council, which was convened by Pope John XXIII in 1962, also spoke on the issue of the Papal authority:
In spite of what appears to be very clear official statements on the subject of the authority of the Encyclical Letters, Catholic opinion, both lay and priestly, has at times diverged widely from the statements in such documents. Perhaps the most telling recent example of this is the controversy surrounding the Encyclical Letter Humanae Vitae of Pope Paul VI, issued in 1968 on the subject of birth control and contraception.