In such cases, according to probabilism, one may safely follow a doctrine approved by a recognized Doctor of the Church, even if the opposite opinion is supported by—or "more probable" as judged by—other criteria, such as those of science or other authoritative sources.
This view was advanced by the Spanish theologian Bartolomé de Medina (1527–1581) and defended by many Jesuits such as Luis Molina (1528–1581).
It was heavily criticised by Blaise Pascal in his Provincial Letters as leading to moral laxity.
The prevailing theory holds that if five or six theologians, notable for prudence and learning, independently adhere to an opinion their view is highly probable, if it has not been set aside by authoritative decisions or by intrinsic arguments which they have failed to solve.
Even one theologian that is regarded as highly authoritative, such as St. Alphonsus Liguori, is able to make an opinion probable in this sense.
If one opinion is not only less safe (in that it goes against the law) but also speculatively uncertain, then it is prohibited by Probabilism, until all reasonable effort has been made to remove the uncertainty, by considering the arguments on both sides and by consulting available authorities.
Probabilists apply their theory only when there is question merely of the lawfulness or unlawfulness of an action, because in other cases certainty might be demanded on various grounds, as happens when the validity of the sacraments, the attainment of an obligatory end, and the established rights of another are concerned.
Finally, probabilists insist that the opinion in favour of liberty must be based on solid arguments and not on mere flimsy reasons which are insufficient to gain the assent of prudent men.
[1]: 83–4, 88–94 Fathers, doctors and theologians of the Church at times solved cases on principles which apparently were probabilist in tendency.
Augustine of Hippo declared that marriage with infidels was not to be regarded as unlawful since it was not clearly condemned in the New Testament: "Quoniam revera in Novo Testamento nihil inde praeceptum est, et ideo aut licere creditum est, aut velut dubium derelictum".
However, many theologians were Probabiliorist in their principles before the sixteenth century, including Sylvester Prierias,[6] Conradus,[7] and Thomas Cajetan.
In his Expositio in 1am 2ae S. Thomae he wrote: If an opinion is probable it is lawful to follow it, even though the opposing opinion is more probable.His system soon became the common teaching of the theologians, so that in the introduction to his Regula Morum Father Terill maintained that until 1638 Catholic theologians of all schools were probabilists.
Jansenist Rigorism spread into France, and Pascal attacked probabilism in his Lettres Provinciales, which were in turn condemned by Alexander VII in 1657.
This opinion was in vogue before the time of Medina, and was renewed in the middle of the seventeenth century as an antidote against Laxism.
Thyrsus Gonzalez, a Jesuit professor at the University of Salamanca, favoured Probabiliorism in his Fundamentum Theologiae Moralis (1670–72).
Many of the moderate probabilists of the sixteenth and seventeenth centuries foreshadowed in their writings the theory to which, in his later-days, St. Alphonsus adhered.
This view gained vigour and persistence from the teaching of Alphonsus Liguori, who began his theological career as a Probabiliorist, subsequently defended probabilism, especially in a treatise entitled Dissertatio scholastico-moralis pro usu moderato opinionis probabilis in concursu probabilioris (1749, 1755), and finally embraced Æquiprobabilism about 1762.
In the sixth edition (1767) of his Moral Theology he again expressed these views and indeed towards the end of his life frequently declared that he was not a probabilist.
As a matter of fact, a comparison between the "Moral Theologies" of moderate probabilists and of Æquiprobabilists shows little practical difference between the two systems, so far at least as the uncertainty regards the existence as distinguished from the cessation of a law.
Francis Ter Haar and L. Wouters engaged in controversy with August Lehmkuhl who, especially in his Probabilismus Vindicatus (1906) and in the eleventh edition of his Theologia Moralis (1910), strongly supported the probabilist thesis which had been accepted during the nineteenth century by most theologians.
Probabilism, if untrue, is seriously detrimental to the spiritual life of the faithful, since it permits actions which ought to be forbidden, and the Church cannot tolerate or give approval to such a moral system.
That the Church has given positive approval to probabilism in the person of St. Alphonsus is proved from the fact that his works including his treatises in favour of probabilism, received official sanction from the Decree of 18 May 1803, the reply of the Sacred Penitentiary of 5 July 1831, the Bull of Canonization of 26 May 1839, and the Apostolic Letters of 7 July 1871 (cf.
Æquiprobabilists reply to this argument that when the less safe opinion is certainly less probable than the safe opinion, the former has lost solid probability and consequently cannot, so far as conscience is concerned, obtain the privileges which the Divine Legislator, the Church, and the State concede in the case of really doubtful laws.
But when there is a solidly probable opinion in favour of liberty, the law has not been sufficiently promulgated, since there has not been the requisite manifestation of the mind of the legislator.
It would be begging the question to assume that no obligation is imposed simply because there is a probability that the law has not been sufficiently promulgated.
But, so long as there is a solidly probable opinion in favour of liberty, there is invincible ignorance about the obligation imposed by the law.
But they must admit that probabilism is more probable than Æquiprobabilism, since the vast majority of theologians favour the milder view, and Æquiprobabilists do not reject external authority.
Many probabilists lay stress on a practical argument in favour of their opinion, which is derived from the difficulty of distinguishing between various grades of Probability.
– Probabilists reply that their system can be of no use to those who do not look on it as certainly true; but the fact that many theologians do not accept it does not prevent its adherents from regarding it as certain, since these can and do believe that the arguments urged in its favour are insuperable.
Probabilism is seen by some Catholic authorities as an easy road to Laxism, because people are often inclined to regard opinions as really probable which are based on flimsy arguments, and because it is not difficult to find five or six serious authors who approve of opinions which right-minded men consider lax.