That an act, therefore, be morally good, or justifiable, (a) the whole train of the tendency of the will must be good; that is, (1) the object, (2) the end, (3) and the circumstances must be good; or (b) the intention should be good, and the remaining elements in the train of will-tendency are to be indifferent. That an act be morally bad it is enough that the object, the end, or the circumstances be inexcusably bad.
There may be honest doubt as to the existence of evil in the circumstances or the end, and here enters the matter of probability; but apart from this, some general rules of morality that govern all cases may be formulated:
1. An intention or end which is gravely evil always makes the entire action evil and unjustifiable.
2. An intention or end which is slightly evil, if it is the entire end of an action, makes the whole action evil but not gravely evil—makes it, say, a venial sin and not a mortal sin.
3. If an intention or end which is venially evil accompanies secondarily a good intention or end, and is rather a motive than the real effective agent in attracting the will, this venial evil does not vitiate the whole goodness or righteousness of the main action. Compare the remarks made above in discussing an action that has a double effect, partly good and partly bad.
4. Circumstances that are gravely evil practically vitiate the entire action, but circumstances which are venially evil do not always vitiate the entire action.
Much might be said here concerning conscience as a judge of the morality in an act, but this discussion is not necessary for our present purpose. Like other men, physicians often confuse conscience with inclination, or at best with unfounded opinion. When conscience is to be a rule of action it must [{16}] have at the least moral certitude; or, what is different but practically the same thing, the opinion of conscience must be at the least genuinely probable. The term "probable" is used here in a technical sense, and it will be so used throughout the remainder of this article.
The doctrine of Probabilism is connected with the promulgation of law. A law, according to St. Thomas (op. cit. I. 2., q. 90, a. 4) is: "Ordinatio rationis ad bonum commune ab eo qui curam habet communitatis promulgata." Sometimes it is not evident whether or not a law binds in a particular case, and in such a condition, that is, in which there is question solely of the existence, interpretation, or application of a law, we may follow a probable opinion which assures us the act is licit, although the opinion which says the act is illicit may be just as probable or even more probable. This is the fundamental proposition of Probabilism, which is the doctrine especially of St. Alphonsus Liguori, but it was held centuries before his time. As the church has never condemned this doctrine, but rather tacitly approved of it, Catholics may safely follow it, and those that are not Catholics will find it very reasonable.
A law which is doubtful after honest and capable investigation has not been sufficiently promulgated, and therefore it can not impose a certain obligation because it lacks an essential element of a law. When we have used such moral diligence of inquiry as the gravity of a matter calls for, but still the applicability of the law is doubtful in the action in view, the law does not bind; and what a law does not forbid it leaves open.
Probabilism is not permissible when there is question of the worth of an action as compared with another, or of issues like the physical consequences of an act. If a physician knows a remedy for a disease that is certainly efficacious and another that is probably efficacious, he may not choose the probable cure, at the least in a grave illness. Probabilism has to do with the existence, interpretation, or applicability of a law, as I said, not with the differentiation of actions.
The term probable means provable, not guessed at, or jumped at without reason. There must be sound reason [{17}] adduced to constitute probability. The doubt must be founded on a positive opinion against the existence, interpretation, or application of the law. It must be more than mere negative doubt, more than ignorance, more than vague suspicion, especially must it be more than a sentimental impression. There is a mental condition, which easily passes over into disease, wherein a man habitually can not make up his mind. This flabbiness has nothing to do with Probabilism. The opinion against a law to constitute Probabilism must be solid. It must rest upon an intrinsic reason from the nature of the case, or an extrinsic reason from authority,—always supposing the authority cited is really an authority. Many men sitting upon the supreme bench in the Court of Science and called authorities by friends and newspapers, are only fools in good company.
The probability must also be comparative. What seems to be a very good reason when standing alone may be very weak when compared with a reason on the other side. When we have weighed the arguments on both sides, and we still have good reason left for standing by our opinion, our opinion is probable. The probability is, moreover, to be practical. It must have considered all the circumstances of the case.
The principles presented here have been arranged, as we said, with a view toward application in judging the morality of actions that may occur in cases of ectopic gestation, and we shall apply the doctrine of probabilism in the question, does the commandment "Thou shalt not kill" bind in certain cases of ectopic pregnancy? It is also necessary to add the principles underlying our duty to preserve human life.