642. Those persons who act with a doubtful conscience, and later discover that what they feared might be wrong was not wrong, or not so bad as they suspected, must bear in mind: (a) that their past conduct is not to be judged by their newly acquired knowledge, for that conduct must be judged by the knowledge had at the time. Example: Sempronia does some work on Sunday, doubting whether she is committing a grave or a slight sin. Later she discovers that it was really only a venial sin, and she congratulates herself that she did not sin seriously. Her judgment is wrong, because she did not know at the time of the work that it was not a grave sin; (b) that they must guide themselves in future acts by their newly acquired knowledge.
643. Kinds of Certitude.—Judgments may be certain in a greater or less degree.
(a) They are metaphysically certain, when error is absolutely impossible, the opposite of what is held by the mind being a contradiction in terms which omnipotence itself could not make true. Example: The judgments that the same, identical act cannot be both good and bad, that good is to be done and evil to be avoided, that God is to be honored, are metaphysically certain, since they result immediately from the very concepts of being, of goodness, and of God.
(b) Judgments are physically certain, when error is impossible according to the laws of nature, the opposite of what is held by the mind being unrealizable except through intervention of another cause. Example: The judgments that he who takes poison will destroy life, that he who applies fire to a house will destroy property, are physically certain. because natural agencies, like poison and fire, act infallibly when applied to suitable matters and under suitable conditions and left to their course, unless they are overruled by superior power.
(c) Judgments are morally certain, when error is impossible according to what is customary among mankind, the opposite of what is held by the mind being so unlikely that it would be imprudent to be moved by it. Examples: One is morally certain that what a reputedly truthful and competent person relates to one is true. A person is morally certain that a conclusion he has drawn about his duty in a particular instance is correct, if he believes that he has overlooked no means of reaching the truth. Testimony and inference, since they come from free and fallible agencies, may lead into error; but, when they appear to have the requisite qualities indicative of truth, they are for the most part reliable and in practical life have to be considered as such.
644. As to the certainty that is required in the judgment of conscience, the following points must be noted:
(a) Metaphysical certainty is not required, since conscience does not deal with primary propositions, but with deductions about particular acts. The first moral principles, which are the object of synderesis, and at least some of the general conclusions, which are the object of moral science, are metaphysically certain (see above 145, 300), as they are based on necessary relations; but the particular conclusions, which are the object of conscience, are concerned with the contingent and the individual.
(b) Physical certainty is not required for the judgment of conscience, since conscience is not concerned with the activities of natural agents, but with the activities of moral agents that act with freedom and responsibility.
(c) Moral certitude, therefore, is sufficient for the conclusions drawn by conscience. That a higher kind of certitude is not necessary should not surprise us, for it would be unreasonable to expect that the same degree of assent be given to judgments that are concerned with particular and contingent cases as to those that are concerned with universal and necessary principles.
645. Moral certitude is of two kinds: (a) certitude in the strict sense, which excludes not only the fear of error, but every doubt, prudent and imprudent, great and small, Example: Titus thinks of a way in which he could easily make money dishonestly; but his conscience sees that the thing is manifestly wrong and decides without the slightest fear or doubt that it must not be done; (b) certitude in the wide sense, which excludes all fear of error and every serious or prudent doubt, but not one or other slight and imprudent doubt. Example: Caius was baptized by an excellent priest, but the date was omitted in the register. The doubt occurs to Caius that perhaps something essential was also omitted, and that it may be his duty to seek another Baptism. His doubt is unreasonable.