EQUIPROBABILISM. - Called by its supporters moderate probabilism as well, it is one of the so-called moral systems, whose first defender seems to have been the Jesuit C. Raseler (1654-1723). Equiprobabilism admits the fundamental principle of probabilism, that a doubtful law does not oblige. But it tempers this in two ways. First of all, it adds that the law is not truly doubtful unless the opposing opinions enjoy an equal (aequus, whence "equiprobabilism") degree of probability. If the opinion favoring the law is certainly more probable than the opposite opinion favoring liberty, the former in fact becomes morally certain and therefore obligatory. And in this equiprobabilism agrees with probabilism (v.). Furthermore, even in the case where the opinions are nearly equal on both sides, law and liberty, equiprobabilism introduces a new distinction, applying another principle, the principle of possession (in dubio melior est condicio possidentis). Law and liberty are conceived as two contending parties: the latter with the native faculty of choice, the former with the binding force of obligation. In man's conscience, tormented by doubt, each claims priority of possession, according to priority of existence.
In the case of doubt whether the law has ceased through abrogation, dispensation, etc., or whether the obligation imposed by it has been fulfilled, the law has precedence and therefore, as the equiprobabilists say, it holds possession against liberty. Consequently man is bound to act as if the law had not really ceased or the obligation had not been fulfilled: cessation and fulfillment are facts that must be proved before being admitted.
If, on the other hand, man strictly doubts the very existence, meaning or extent of the law, then priority belongs to liberty and therefore it is liberty that holds possession against the law. Consequently man may consider himself free from the obligation. For example, the young man who doubts whether he has completed his 21st year is not bound to fast (doubt about existence); on the contrary, the old man who doubts whether he has reached his 60th year is bound to it (doubt about cessation).
Two serious questions are linked to this system: the first on the intrinsic value of equiprobabilism, the second on the genuine thought of St. Alphonsus regarding the moral systems. Turning to the second question, it is not our task to settle a controversy which, begun in the time of Ballerini (1863) and protracted for half a century, has by now died down, though without the contenders having laid down their arms or abandoned their positions. Nevertheless, for anyone who objectively examines this historical question it is difficult not to admit that St. Alphonsus, having started out from probabiliorism, was for a considerable period of his life a probabilist, and, from 1762, an equiprobabilist. In explaining these changes one cannot disregard the particular historical moment of bitter controversy in which the holy doctor found himself and his personal experiences.
Regarding the intrinsic value of the system, its opponents particularly reproach equiprobabilism for the misplaced application of the principle of possession, which is valid only in matters of justice, where one can distinguish between possession of a thing and the right to it, which is not possible with respect to the law.
Today all the Liguorian school adheres to equiprobabilism, that is, the moralists of the Congregation of the Most Holy Redeemer, and certain others, such as Th. M. Gousset (Théologie morale à l'usage des curés et des confesseurs, I, 4th ed., Paris 1846, pp. 80-88); S. Beaudonin O. P. (De conscientia, Tournai 1911, pp. 99-138), A. D. Sertillanges O. P. (La philosophie morale de st Thomas d'A., Paris 1916, p. 554).
BULL. Editions c.l., of St. Alphonsus, Theol. morali, Homo Apostolica and eleven monographs, all listed together in: M. De Meulemeester, Bibliographie générale des écrivains rédemptoristes, I. Bibliographie de st Alphonse M. de L., Louvain 1933 and in J. Aertyns-C. Damen, Theol. mor., I, 15th ed., Turin 1947, p. XXXVII. - Studies: A. Ballerini, Dissertation de mor. syst. s. Alph., Rome 1864; id., Tradizios Alphourianos, I, 1, 2nd ed., Paris 1874; id., De mor. syst. s. Alph., Rome 1874; L. Gaudé, De mor. syst. s. Alph., ibid. 1894; J. de Caigny, Apologetica de aequiprob. Alphourian, Tournai 1894; J. Ter Haar, De syst. morali antiquorum probabilitarum, Paderborn 1894; J. Aertyns, Probabilismus oder Aequiprobabilismus, Gulpen 1896; G. Arendt, Apologetica a de Caigny exoratae crisis, Freiburg im Br. 1897; X. Le Bachelet, La question liguorienne, Prob. et équiprob., Paris 1899; I. L. Janson, La question liguorienne; rép. au p. Le Bachelet, Galoppe 1899; J. de Caigny, De genuino probabilismo licito, Bruges 1901; I. Ter Haar, Ven. Innoc. XI de prob. decreti hist. et vindiciae, Rome 1904; id., Geschichte u. Kritik im Dienste der Minus probabilis, Paderborn 1906; P. Lehmkuhl, Prob. vindicatus, Freiburg im Br. 1908; L. Wouters, De minusprobabilismo, 2nd ed., Amsterdam 1908; J. de Caigny, De genuino systemate s. Alphonai, Bruges 1909; G. Arendt, Aequiprobabilismus ab ultimo fundamento discussus, Rome 1909; S. Mondino, Studio storico-critico sul sistema morale di s. Alfonso, Monza 1911; L. Wouters, De syst. mor., 2nd ed., Gulpen 1918; I. De Blic, Probabilisme, in DFC, III, pp. 320-40; I. B. Raus, St Alphonse et les variations de nos systèmes morale, in Novo. rev. libel., 23 (1928), pp. 241-64, 334-55; P. Delatuc, Le système moral de st Alphonse, St-Etienne 1908; C. Damen, S. Alphonse doctor prudentiae, in Rassegna di diritto e morale, 5 (1929), p. 220; 6 (1940), p. 220.
Pietro Palazzini