646. Moral certitude in the wide sense is sufficient for a safe conscience, even in matters of great importance, since it is frequently the only kind of certitude one can have, and he who would strive to be free from every slight and baseless suspicion would be soon involved in a maze of scruples and perplexities. Example: If the Caius above referred to were to yield to his doubt and be rebaptized, a similar doubt about the second Baptism might easily arise in his mind, and he would be no more contented than before.
647. From the point of view of its object, certitude is twofold. (a) Speculative certitude refers to a judgment considered as a general law, abstraction being made from particular circumstances. Example: It is speculatively certain that farm work on a holyday is a forbidden kind of work, and that clerics are obliged to say the Divine Office. (b) Practical certitude refers to a judgment which is an application of a general law to a particular case, consideration being given to all the pertinent circumstances. Example: It is practically certain that Titus may make hay on a holyday, if otherwise he will suffer great loss; and that a cleric is excused from the Divine Office, if his physician has warned him that he is physically or mentally unable to perform it.
648. Speculative certainty is not sufficient for conscience, but practical certitude is required, since conscience refers not to abstract laws but to concrete cases—not to what is right if only the object of the act is considered, but to what is right when one considers the object, the motive, and all the circumstances here and now present.
649. From the point of view of the arguments on which it is based, certitude is of two kinds. (a) Demonstrative certitude is the assent that rests on a conclusion logically drawn from certainly true premises. Example: Caius argues that he is obliged to go to Mass on Sunday, because the law is certain, and it is also certain that the law applies to him. (b) Probable certitude, which is the assent that rests on a conclusion, whose premises, though not certain, seem to be true, and against which there is no counter conclusion, or none that cannot be readily answered (see 703). Example: Caius is pretty sure that he is seriously ill, because he perceives a number of alarming symptoms; the possibility that these may be due to imagination is excluded by the fact that they are new and sudden. Caius, therefore, concludes that he may hold himself excused from attendance at Mass.
650. Probable certitude is sufficient for conscience, for in moral matters it is impossible to have at all times reasons that amount to a demonstration, and hence a person acts prudently in following a decision that is solidly probable and unopposed by any contrary serious probability. What is called “probable certitude” here is very different from probable opinion, about which there will be question below (662 sqq.)
651. From the point of view of the manner in which it is obtained, certitude is again twofold. (a) Direct certitude is that which is obtained from principles that are intrinsic to the case by applying to the matter the law concerning it. Examples: A judge who decides according to the evidence and proofs given in court that an accused is guilty, and a son who concludes from the Fourth Commandment that he is bound to help his parents in necessity, have direct certainty in their judgments, because they argued from principles that deal with the question before them. (b) Indirect certitude is that which is obtained from principles that are extrinsic to the case by applying to the matter in hand reflex principles (i.e., rules that direct how one should act in doubt) or the principle of authority (i.e., the argument drawn from the opinion of those who are acknowledged as competent to decide). Examples; If a judge is not able to form a certain judgment from intrinsic reasons concerning an accused, because strong arguments have been given both for guilt and for innocence, he has recourse to principles that have reference to his own state of doubt, and which declare that he must acquit when he is not certain of guilt. If a man is not able to decide whether the Fourth Commandment obliges him to keep his grandparents or mother-in-law in his home, when they upset his family and are able to take care of themselves, he can have recourse to the external principle of authority by consulting his confessor.
652. Direct certitude is not necessary for the judgment of conscience, for often, as in the cases just mentioned, it is not possible. Moreover, indirect certitude suffices to give one who is in doubt such practical assurance that one’s fears become unimportant and one is able to act prudently in spite of them.
(a) The principle of authority—that “in doubt we can safely follow the advice of those who are experts and truthful”—is reliable, as both the conditions required for authority (viz., knowledge and truthfulness) and also daily experience show.
(b) Reflex principles likewise, although they do not prove what is deduced from them, are well founded, and point so clearly the side to be taken when judgment is suspended between alternatives that they enable one to act with all the certitude that prudence demands. Example: The principle that “in doubt decision should be given in favor of the accused,” is based on the fact that a man’s right to his life and liberty is so certain that he does not forfeit that right unless it is proved convincingly that he is guilty.
653. Examples of uncertain and certain consciences are the following: