4. An opinion presents itself before our minds to be adjudged on. The intelligence, in face of two contradictory courses of conduct, has to determine which is right and is to be followed, and which is wrong and has to be avoided.
(a) An opinion may be slightly probable, when it is founded on motives that are insufficient to determine the assent of a prudent man.
(b) An opinion may be probable, when the motives impelling towards it are strong, but there is a slight probability in favour of the contrary opinion.
(c) An opinion may be certain, when all reasonable doubt is excluded, through the contrary opinion being altogether improbable.
When the opinion is certain, then it must be accepted and followed. When, however, it is only probable, or slightly probable, then the judgment must be called in to pronounce on the probable consequences. Hitherto we have considered the eye as turned to God as the sole author of law; but in such cases as there is no certainty, only probability, the Conscience is assisted by prudence, which is the action of the reason judging of the probable consequences of an act.
When the moral sanction is certain, prudence is not called in to alter the conduct essentially, only that it may order it so as to be carried out advisably; but when an opinion is probable, and not certain, then the eye of the reason may be, and ought to be, directed to the future consequences, and the judgment formed, not only on the antecedent probabilities, but also on the probable consequences, good or evil. As prudence can only judge future probabilities, it may not countermand what has certain sanction. Very often the consideration of probable consequences assist us in determining the right or wrong of an act, which antecedently is not certain.
