encyclical, originally, a pastoral letter sent out by a bishop, now a solemn papal letter, meant to inform the whole church on some particular matter of importance. Benedict XIV circulated the first known encyclical in 1740. Unlike those in the papal bull, doctrinal statements in an encyclical are not necessarily regarded as infallible; the faithful, however, are bound to give assent. Encyclicals became more numerous after the 18th cent. Leo XIII issued a whole series of encyclicals reorienting Roman Catholic life in the modern world; among these are Aeterni Patris, 1879, on Thomistic philosophy, and Rerum novarum, 1891, concerning the social order. Other noteworthy encyclicals include Pascendi, 1907, by Pius X, on modernism; Quadragesimo anno [in the 40th year, i.e., since Rerum novarum], 1931, by Pius XI, dealing further with social questions; and two by Pius XI not written in Latin—Non abbiamo bisogno, 1931, against Italian Fascism, and Mit brennender Sorge, 1937, against the National Socialist regime in Germany. Among the numerous encyclicals of Pius XII are Mystici corporis Christi, 1943, on the nature of the church, and Sacra virgintas, 1954, on evangelical chastity. The encyclical Mater et Magistra, 1961, by John XXIII, makes current the church's teachings on social matters. Paul VI's Humanae Vitae, 1968, which reaffirms the church's traditional prohibition of contraception, caused considerable controversy. John Paul II's many encyclicals include Laborem Exercens, 1981, on the value of human labor; Evangelium Vitae, 1995, which restated the church's teachings on abortion, birth control, and euthanasia and condemned capital punishment; and Fides et Ratio, 1998, which condemns both atheism and faith unsupported by reason and affirms a place for reason and philosophy in religion. All papal edicts are normally known by their first word or words.
See A. J. Fremantle, The Papal Encyclicals in Their Historical Context (1963).