The doctrine of Probabilism is very important in morality. Any law must be promulgated before it really becomes a law, and promulgation in a rational conscience is sufficient. Sometimes there is rational doubt of the existence, the interpretation, or the application of a law in a given case. Here probability is the only rule we can follow. A law which is doubtful after honest and capable investigation has not been sufficiently promulgated, and therefore it cannot impose a certain obligation because it lacks an essential element of a law. When we have used such moral diligence as the gravity of the 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 where 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 doubtfully efficacious, he may not choose this probable cure. Probabilism has to do only with the existence, interpretation, or applicability of a law, not with the differentiation of actions. The term probable means provable, not guessed at, not jumped at without reason. The doubt must be positive, founded on reason, not a matter of mere ignorance, suspicion, emotional bias. The opinion against a law to permit 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 is really an authority. The probability is to be comparative also. What seems to be a very good reason when standing alone may be weak when compared with reasons on the other side. When we have weighed the arguments on both sides, and we still have a good reason for holding our opinion in a doubtful case, our opinion is probable. The probability is, moreover, to be practical. It must have considered all the circumstances of the case. There is, then, a Supreme Being whom we _must_ obey, who created and owns human life primarily; there is also a moral law. On these facts rests the argument relating to the destruction of human life. How far, then, has a human being dominion over his own life, and, secondly, over the life of any one else? St. Thomas,[2] Lessius,[3] and others offer as one argument to prove suicide is not licit, that it is an injury to society or the state of which the suicide is part, and to which the use and profit of his service rightly belong. Lessius, while developing this proof, acknowledges its weakness. [2] _Summa Theologica_, 1, 2, q. 64, a. 5. [3] _De Justitia et Jure_, lib. 2, cap. 9.