(c) Probabilism does not apply to cases in which there is solid probability for the less safe side, but one doubts whether one can lawfully follow it; for it is always sinful to act with a doubtful conscience (see 641 sqq.). Example: Caius has read in a reliable work of theology that a person in certain circumstances, which are his own, is probably excused from Mass. But the word “probably” makes him uncertain whether he can follow this opinion. 709. For the above-mentioned cases, to which their principle does not apply, Probabilists refer to the rules for a doubtful conscience (see 656 sqq.). The following special rules are given for cases of negative doubt: (a) If the doubt is one of law and insoluble, one is free to act; for it is a general principle that an act may be considered lawful, as long as there is no serious reason to the contrary. Example: Sempronius goes out into the country on Sunday afternoon. An opportunity to fish presents itself, but Sempronius begins to doubt whether there is or is not a church law against fishing on Sundays. As no argument for either side is known to him, he may act on the general principle that what is not forbidden is lawful. (b) If the doubt is one of fact and insoluble, and a prohibitory law is involved, one is free to act; for it is commonly admitted that legislators do not intend their prohibitions, which are restrictions of liberty, to be interpreted with the utmost rigor. Example: Titus is eating a chicken dinner late on Thursday night when his watch stops. As he has no way of discovering the time, he does not know whether Friday or the end of the dinner will arrive first. He may continue the meal, making no undue delays. (c) If the doubt is one of fact, and a preceptive law is in question, one must take reasonable precautions to settle the doubt; for the lawgiver wills that those who are subject to the law should make use of the ordinary means to learn the facts on which obligation depends (see above, 384). If the doubt remains insoluble, one may decide in favor of liberty; for it may reasonably be presumed that the legislator does not intend to obligate those whose obligation remains uncertain. Example: Caius doubts whether he has reached the age of sixty, when the obligation of fasting ends. He should try to discover his real age; but, if he can find no real proofs either for or against the age of sixty, he may decide in favor of sixty, if there are some indications that he is of that age. 710. The solutions given above for cases of negative doubt suppose that there is no other or higher law that forbids one to take the risk of deciding in favor of liberty. Hence, in the following instances one must decide against liberty: