687. The debate between Probabiliorism and its adversaries is not often heard today, as most modern moralists give their allegiance either to Equiprobabilism (a modified Probabiliorism) or to Probabilism.
688. Equiprobabilism.—The doctrine of Equiprobabilism is a middle way between Probabiliorism and Probabilism. Thus: (a) it agrees with Probabiliorism in holding that it is not lawful to follow the less safe, if the safer is more probable, or if the safer is equally probable, and the question is about the cessation of the law; (b) it agrees with Probabilism in holding that it is lawful to follow the less safe, if the safer is only equally probable, and the question is about the existence of the law.
689. The principle that “it is not lawful to follow the less safe, if the safer is equally probable and the question is about the cessation of the law,” is defended as follows by Equiprobabilists:
(a) In real doubt we should decide in favor of that side which is possession. But, when doubt is about the cessation of a law, the law is in possession; for there is no question that it was made. Therefore, in such a doubt we should decide for the safer side, that is, that the law has not ceased.
(b) A certain obligation is not complied with by a doubtful fulfillment. But doubts about the cessation of the obligation of law usually arise from a probability that one has already fulfilled the law. Therefore in such cases we should decide that the law has not been fulfilled—that is, that its obligation has not ceased.
690. The Probabilists reply that: (a) it is not true that, in equiprobability about the cessation of law, the law is in possession; for liberty is naturally prior to law, and hence has possession in doubt; (b) nor is it true that an obligation that has probably been complied with or removed is certain.
691. The Equiprobabilists answer: (a) liberty was in possession, until it was dispossessed by the making of the law; (b) an obligation that certainly existed must be held as certainly in existence, until the contrary is proved; whereas a fact, such as dispensation, abrogation, or fulfillment, is not proved if it is only probable.
692. The principle that “it is lawful to follow the less safe side, if the safer is only equally probable and the question is about the existence of the law,” is defended as follows by Equiprobabilists:
(a) In real doubt we should favor the side that is in possession. But when doubt is about the existence of a law, liberty is in possession; for liberty is prior to law. Therefore, in such doubt we may decide that there is no obligation.
(b) An uncertain law does not oblige, if one is invincibly ignorant of its existence. But, when there are equiprobable reasons against the existence of a law, one is invincibly ignorant of its existence. Therefore, in such cases one is not obliged.