Appendix 7. (603).
More moderate and clearsighted probabilists hold back at this point. They are afraid to press ahead coherently with their system when they see that it could do harm or damage to their neighbour. In cases of this kind, they prefer to deny their own system, and abandon probabilism. Fr. Felice Potestà writes: 'It is not lawful to abandon the more probable and safer opinion, and follow the less probable, if the consequence is certain damage or a danger of serious evil to oneself or a third party' (t. 1, p. 1, n. 74, asser. 2). These words do not explain, however, why we have to avoid the danger of serious evil only, and not light evil as well; or why we must avoid doing certain harm to others, and not probable harm also.
Fr. Domenico Viva agrees with Potestà's assertion, and explains it: 'because avoiding serious harm does not depend often upon the probability of an opinion; for although a given medicine probably serves as a cure, the death, for example, of a sick person will not be avoided unless the probability concurs with the truth of the matter' (in Prop. 1, damn. ab Innoc. XI). Fr. Segneri himself (letter 1, §3, n. 31, and letter 2, §9, n. 37) denies that the less probable opinion can be followed 'when that opinion put into practice results in harm to our neighbour from which he should be protected.' Finally, Fr. Niccolò Ghezzi explains the limitation he believes necessary in the field of probable opinion: 'There is another very noticeable point in which the two teachings under discussion concur absolutely, and must concur. They are agreed in establishing those matters in which the use of more and less probable opinions can be employed.
Both sides affirm that probability must be restricted to opinions that directly regard moral questions alone, that is, questions relative to the law, and cannot be used in questions that regard the nature or quality of things used as means to obtain an end to which a person has to tend. Here too it is unlawful to prefer the less probable, the more probable or the most probable opinion to the safe opinion. For example, a doctor is bound to look after a patient as well as he can. If he has a choice between prescribing more or less effective medicines, he must use the most effective. The same can be said about the minister of a sacrament when he is doubtful about the matter or form of a sacrament; and about the government or minister of state in their decisions about how a country should be ruled; and again about a judge, or father, or tutor, or administrator of a sacred place, or about anyone in fact who has to choose the means necessary for obtaining the end to which he is obliged' (Dialoghi sul Probabilismo, Notizia, p. 23). According to this teaching, 'when a person is held to work for a given end, he must use the most probable means available.' But the great end to which every human being is obliged is at least that of not doing harm to anyone. He must therefore use the most probable means available to this end. In other words, he must to the furthest extent of his power avoid every danger in this matter.