Probabiliorism is the moral system according to which, in a doubt of conscience concerning the morality of a certain course of conduct, one must follow the opinion for law unless the opinion for liberty is certainly more probable—which is equivalent to saying unless it is much more probable. If both opinions are about equally probable, the opinion for law must be followed. This system seems to have been commonly accepted in practice before Bartolomé de Medina, OP, in 1577 enunciated the fundamental principle of probabiliorism. It was revived, especially among Dominicans, through the approval of this system communicated by Alexander VII to the Dominican general chapter in 1656. One of the outstanding defenders of probabiliorism in the 18th century was C. Billuart, OP (1685–1757). St. Alphonsus was a probabiliorist in the early years of his priesthood, but later renounced this system because he thought that some of the decisions of its school were keeping the faithful away from the Sacraments. Few, if any, uphold this system today.
See Also: conscience; morality, systems of; doubt, moral; reflex principles.
Bibliography: d. m. prÜmmer, Manuale theologiae moralis, ed. e. m. mÜnch, 3 v. (10th ed. Barcelona 1945–46) 1:345–346. j. aertnys and c. a. damen, Theologia moralis, 2 v. (16th ed. Turin 1950) 1:101–123. m. zalba, Theologiae moralis compendium, 2 v. (Madrid 1958) 1:676. c. r. billuart, Summa Sancti Thomae, 10v. (new ed. Paris 1874–86) v.4 diss. 5.
[f. j. connell]