(b) If the uncertainty arises from the invincible ignorance of one who is subject to the law, the proposition is true in the sense that no one is a transgressor in the internal forum who fails against a law unwittingly (see 327, 489 sqq.). But an act that transgresses no law is lawful in conscience, for all that is not forbidden is lawful.
722. The adversaries of Probabilism offer the following criticism:
(a) As to the proposition that “an uncertain law does not oblige,” the use of this principle by Probabilism may be considered as a begging of the whole question; for what is in dispute is whether, in case a law is uncertain, there is or is not a higher law that requires one to decide for obligation. It can be shown, however, that there is such a higher law; for the legislator cannot be willing that his ordinances be at the mercy of every uncertainty or loophole which subtle minds can devise, and God cannot be willing that those who are subject to laws should expose themselves to sin by deciding against a law because it appears to them to be of doubtful obligation.
(b) As to the proofs given for that proposition, they proceed from an incomplete enumeration, for a law can be doubtful on account of vincible ignorance, as well as for the reasons given. And no one will maintain that vincible ignorance excuses.
723. The Probabilists reply: (a) The principle that “an uncertain law does not oblige,” cannot render law nugatory, since there is question here only of honest doubt, not of pretended or responsible ignorance. Neither can that principle expose one to the danger of formal sin (see 249), since it is supposed that he who follows it is convinced that it is true, and that he has the right to regulate his conduct by it. It does expose to the danger of material sin (see 249), since the law about which there is uncertainty may be existent; but we are not obliged to avoid every danger of material sin, else we should be under the intolerable necessity of fulfilling not only all certain, but all uncertain duties. Moreover, the danger of material sin is not avoided by any moral system except Tutiorism, since even equiprobable and more probable opinions may be false.
(b) The enumeration of cases of doubtful law is sufficient; for, as just remarked, only those cases are being considered in which one is judging about one’s duty in good faith.
724. The second proposition used above as the Minor of the argument for Probabilism—that “a law is uncertain whenever there is a solidly probable opinion against its existence or for its cessation”—is defended by the very definition of the term “uncertain.”
A thing is said to be accepted as certain when one yields it firm assent and has no serious misgivings that it may be false; hence, the uncertain is that which is not assented to firmly (the doubtful), or that which does not exclude serious doubts about its truth (matter of opinion). Now, a law whose existence or obligation seems likely, but against which there militates a solidly probable argument, is not so firmly established as to inhibit every prudent doubt. In other words, such a law is uncertain.
725. Criticism of the Argument in the Preceding Paragraph.—(a) The supposition on which the argument rests is false. It supposes that the interpretation of the legal axiom that “a doubtful law does not oblige,” should be drawn from the philosophical definition of the terms, whereas it should be drawn from the sense given it by other rules of law. Now, there are canonical rules which declare that in doubt one should follow that which has possession, or that which seems more probable. Hence, the axiom quoted by the Probabilists refers only to cases of negative doubt; the other two rules refer to cases of doubt in the wide sense, or to cases of opinion; otherwise, we should have to admit that these legal maxims are contradictory, one to the other. Thus, it appears that Probabilism is based on a principle formulated to solve difficulties of an entirely different kind from those which the system deals with.
(b) The argumentation itself is fallacious. It takes for granted that an opinion is certainly and solidly probable, not only when it has no opposite or when its opposite is less probable, but also when its opposite is equally or more probable. This cannot be. Solid probability on the other side of a question must create doubt about an opinion held, and so make it at best uncertainly probable or probably probable; while greater likelihood or presumption on the other side must make one’s own opinion appear imprudent and unworthy of a rational being, and therefore not solidly probable.