693. The principle that “it is not lawful to follow the less safe side if the safer side is more probable,” is defended as follows by Equiprobabilists:
(a) In doubt improperly so called—that is, in that condition of mind in which there is no fluctuation between equal arguments, but only some indecision between the more and the less probable—we should decide in favor of the more probable, as being morally certain. Hence, it is not lawful to follow what is less safe and less probable.
(b) A law sufficiently promulgated obliges. But, when it is more probable that a law was made or is in force, such law is sufficiently promulgated to the conscience. Hence, the safer side must be followed, if it is more probable.
694. Probabilist Criticism of the Foregoing Arguments.
(a) If the excess of the more probable over the less probable is so great that the latter is only slightly or doubtfully probable, the more probable is equivalent to certitude; for certitude is assent without fear of the opposite, and the fear of the opposite in such a case would be so slight that it may be considered as non-existent. If the excess is not so great, the less probable remains solidly and certainly probable, and the more probable is not certitude, but opinion (that is, assent with fear of the opposite). The Equiprobabilists are speaking of greater probability in the second sense, and hence they are wrong when they identify it with certitude (see above, 654).
(b) A law must be so promulgated to the conscience that one knows the law or could know it with sufficient diligence; it does not suffice that one can get no further than opinion. It would be unreasonable to oblige one to observe not only what is the law, but also what seems to be the law. Now, he who has only more probable opinion that he is bound by some law, does not know that such obligation exists; he only knows that it seems to exist.
695. Reply of the Equiprobabilists.-(a) The more probable always removes the appearance of truth from the less probable. Hence, he who recognizes an opinion as more probable can assent to it without any fear of error.
(b) One who holds it as more probable that he is obliged by a certain law, does not know for certain that he is obliged by reason of that law; but he does know for certain that he is obliged by reason of a higher law. Superior to every particular law is the general law that nothing may be done that will deprive law of its efficacy. But law loses its efficacy if each one is free to decide that he is not bound even when the greater weight of probability is to the contrary.
696. General Arguments in Favor of Equiprobabilism.—(a) From Authority.—St. Alphonsus Liguori, who holds a unique place in the Church as a moralist, preferred Equiprobabilism to every other moral system; and his views are followed not only by his own Congregation, the Redemptorists, but by many others.
(b) From Comparison with Other Systems.—Truth lies midway between extremes; for truth is lost either by exaggeration or by defect. But Equiprobabilism is a happy medium between Probabiliorism inclining to Rigorism, and Probabilism inclining towards Laxism. Hence, the relation of Equiprobabilism to other systems is in its favor.