PROBABILISM: A doctrine of Roman Catholic moral theology that in case of ethical problems the course of conduct to be adopted should be determined by what is adjudged to be probably right, with due support of precedent and authority recognized by the Church. Analogues to the system may be found among later Greek philosophers, particularly the Neo-Academics Carneades and Clitomachus, as well as in the distinction drawn by Cicero (De officiis, i. 3) between "perfect duty" and "medium duty," for the performance of which "a probable reason may be assigned." A tendency toward probabilism early became evident in the Church, as in the admissibility of a certain degree of "pious fraud" in the theory of the Greek Fathers after Chrysostom. It was further developed in the medieval Penitential Books (q.v.) with their frequent formula "there is no harm" in regard to matters ethically equivalent or indifferent; and it received a powerful impulse in the balancing of conflicting authorities by the scholastic casuistry of the last three centuries of the Middle Ages. Here reference need only be made to the Summa Angelica of Angelus Carsetus (d. 1495), the Summa rosella of Giovanni Baptista Trovamala (fifteenth century), the Regul morales of Jean Charlier Gerson (q.v.); and the Dominicans of the sixteenth century, particularly the school of Melchior Cano (q.v.). Bartolome de Medina (d. 1581), followed by Domingo Bañez (d. 1604), enunciated the doctrine that "if an opinion is probable, it may be followed, even though a more probable opinion be opposed." With these precedents Jesuit moralists, after the beginning of the seventeenth century, developed the doctrine of probabilism with extreme subtility and logic. Probabilism was formally introduced into the courses in moral theology by Gabriel Vasquez in 1598; and Antonio Escobar y Mendoza (q.v.) defended the tenet that an ethical judgment supported as probable by a recognized authority might unhesitatingly be preferred to another opinion which was safer and more probable. This principle affected the confessional, since a penitent who could appeal to a probable opinion must be absolved by his confessor, even though the latter were of a different opinion; while attrition was probabilistically made to suffice for contrition. Escobar likewise taught that the great number of divergent moral opinions is one of the chief proofs of the goodness of divine providence, since the yoke of Christ is thus made easy. Hermann Busenbaum (q.v.), in similar fashion, warned against giving too much weight to excessive scruples of conscience, and urged that in each case the mildest and safest opinion should be followed. Probabilistic arguments were also used in defense of such teachings as the distinction between philosophical and theological sin and mental reservation.
As early as 1620 the Sorbonne protested against the doctrine of probabilism, and in 1656 Pascal attacked it in his "Provincial Letters." Renewed protests of the Sorbonne in 1658 and 1665 led Alexander VII. to condemn probabilism and the moral theories connected with it (Sept. 24, 1665). Opponents of the doctrine arose within the Jesuit order, among them Paolo Comitoli (d. 1626) and Michael de Elizalde; Innocent XI., in 1679, condemned sixty-five probabilistic theses as laxistic. In 1687 the thirteenth general congregation of the Jesuits officially declared that the Society of Jesus was not opposed to anti-probabilism, although when Tyrso Gonzalez, the Jesuit general, attacked probabilism in his Fundamenta theologi moralis (Dillingen, 1691), he encountered the most strenuous opposition from his order. A severe blow was dealt probabilism when, in 1700, the assembly of the clergy of France forbade it to be taught. Additional Jesuit authors also opposed it, though its most unsparing enemies were the Dominicans. The net result was a series of modifications of probabilism, of which the Jesuit casuistry of the eighteenth century evolved three chief types. These were equiprobabilism, according to which one of two moral opinions may be followed only if it is exactly as probable as the other; probabiliorism, in which, if the probabilities are not equal, that which is more probable must determine the course of action; and tutiorism, according to which the safer, rather than the more probable, opinion is to be followed. See CASUISTRY.