677. A modified form of Tutiorism taught: “When one is undecided between the safer and the less safe, one must choose the safer, unless the less safe is most probable.” This system has not been censured by the Church, but Catholic theologians with hardly an exception have rejected it, for the following reasons: (a) Most probable, as understood by the defenders of this system, is that which has such likelihood and such appearance of truth as to remove every probable danger of even material sin. Thus, in reality this system requires absolute certitude and agrees with the rigorous tenet of Tutiorism that even a most probable opinion against the law may not be followed. (b) Most probable, as commonly understood, is that side of a question which so far excels the other side that no answer can be given to any of its arguments, while all the arguments of the other side can be answered. To require this in moral difficulties is to require the impossible, for even the greatest theologians have to be content at times with less. 678. We are obliged always to follow a safe course, that is, not to expose ourselves to the danger of formal sin (see 249, 258); but Tutiorism errs when it teaches that we are also obliged always to follow the safer or safest course, that is, never to expose ourselves even to the danger of material sin. There are cases, however, when we are obliged (because some law requires it) to follow a safer course, that is, not to expose ourselves or others to some great harm. Thus, we must follow the safer side in the following cases: (a) when there is question concerning something essential for the salvation of ourselves or of others, for the law of charity forbids that any risk be taken in this supremely important matter. Example: Titus instructs the dying Caius only concerning the existence of God and of the future life. He should also instruct him about the Trinity and the Incarnation, which is the safer course, since it is more probable that an explicit faith in these two mysteries is a condition of salvation; (b) when there is question of some great spiritual loss or gain for ourselves or others, for justice or charity forbids that we take chances in such affairs. Examples: Sempronia doubts whether she is excused from the law of abstinence, and whether she will be guilty of sin if she eats meat. Caius doubts whether attendance at a certain school will do harm to the religion of his son. Balba doubts whether she is bound to inquire about the truth of her sect. As long as their serious doubts remain, these persons should follow the safer course; (c) when there is question of the validity or invalidity of a Sacrament, for the virtue of religion requires that the Sacraments be administered with fidelity, and be not exposed to the peril of nullity. Example: It is not lawful to consecrate matter that has probably been substantially adulterated;