(b) Against the judgment there must be no decisive argument from authority or reason. Example; The judgment that a certain course of action is lawful because St. Alphonsus permits it, is ordinarily solidly probable; it is not probable, however, if the opinion of St. Alphonsus (e.g., that Catholics may act as sponsors in non-Catholic baptisms) has been disallowed by the Church, or if the argument he uses (e.g., that concerning the amount that constitutes grave matter in theft, which reasons from conditions in his day) is not strong. (c) The arguments for the judgment must retain their probability, if they are set over against the arguments for the opposite. Manifestly, if the arguments are all satisfactorily answered by the opposite side, the judgment based on them ceases to retain the appearance of truth. Probabilism does not require, however, that one determine the relative degrees of probability in opposite opinions. 706. It is not sufficient according to the Probabilists that another be certain of the probability of an opinion; but the person who follows the opinion must himself be certain that it is solidly probable. 707. Regarding the kind of authority necessary to make an opinion solidly probable from external evidence, Probabilism teaches: (a) that absolute probability (that is, such a weight of authority as would appear strong even to the most learned) ought to be estimated by quality rather than quantity--by the learning, prudence, impartiality, and independent study of the authors, rather than by their numbers. If five distinguished moralists arrive by separate study at the same conclusion (i.e., that an opinion is probable), or if one of special reputation in a matter under question supports the probability of an opinion, the argument from authority is strong; (b) that relative probability (that is, such a weight of authority as suffices for one who is unlearned, such as a child, a halfwit, an uneducated person) is had sufficiently through the word of only one person who is looked up to as a guide or instructor, such as a parent, confessor, or teacher. 708. Probabilism supposes that one regards the opinion one follows as truly probable, and that one is convinced that it is lawful to follow such an opinion. Hence, the system does not apply in certain cases. (a) It does not apply to cases in which there is no probability on either side--that is, to cases of negative doubt (see 656 sqq.), whether the doubt be of law or of fact. (b) Probabilism does not apply to cases in which there is only slight or uncertain probability for the less safe side. Example: Caius has heard that a certain novel opinion is defended by a recent author, but he is uncertain of the author’s standing as a theologian, and he realizes that the fact that a man has written a book does not make his ideas solidly probable.