The view that, if there is doubt about the rightness of any course of action, that action is to be preferred which is probably right, even though the action which is more probably right is also the action that is in accord with the law. (“Probably” is not used in a statistical sense: a probable opinion is the opinion of some doctor gravis et probus.) The view, which is one of several approaches that have been adopted in areas of moral uncertainty, was unknown before the end of the sixteenth century. It was formulated, or perhaps first given prominence, by Bartholemew Medina (1527-81) and rapidly gained hold.

The rationale of the view lies in the need for casuists in the Roman Catholic Church to balance the verdicts of conflicting church authorities. Probabilism was developed as a casuistical device by the Jesuits, as against Probabiliorism,* the view that the libertarian course of conduct is to be preferred only if it is more probable than the view that is in accordance with the law. The presence of many contradictory moral authorities in the Roman Church created endless possibilities of going against the legally accepted view by this approach.

Other competing views, besides Probabiliorism, are Rigorism, which holds that only if the less safe opinion is most probable can it be practiced, and Laxism,* which maintains that an only slightly probable opinion could be followed with good conscience.

Probabilism was one of the matters strongly controverted by the Jansenists* in their battle with the Jesuits in the seventeenth century. The Jansenists took a Probabilioristic or Rigoristic view. Pascal made Probabilism, and the ethos in which it flourished, notorious in his Provincial Letters (1656). Pope Alexander VII* condemned the teaching in 1665 after continued protests from the Sorbonne, and in 1700 the Assembly of the clergy of France forbade it to be taught.