Summa summae S. Thomae, Tomus II

[From the distinctions prefixed it is plain that probability is here understood by us insofar as it affects, not the intellect in speculative matters, but conscience in things to be done. Moreover actions are determined and imposed by law. Law, therefore, as it ought here to be considered, is the will of a superior concerning what he wills or wills not to be done, made manifest to the subject. If the law be altogether and invincibly unknown through defect of promulgation or of cognition, the action repugnant to it is called material sin, or matter of sin; but if the law be known, or vincibly and culpably ignored by the agent acting against it, the sin is formal, because the will of the inferior contradicts the will of the superior, and thus is inordinate and evil. It happens however not rarely that the subject can neither affirm nor deny the existence of the law, opposite arguments contending for it and against it. Then the law is merely probable or doubtful; and since obligation is an effect of law, the question is raised whether the subject is then held to obey such a law, or is immune from it.

We must therefore treat solely, in the present question, of the licit or illicit alone, that is, of the honesty of an action against a probable or doubtful law posited. This must always be held before the eyes in this dissertation, lest certain confusions be incurred which would render the matter inextricable, and of which there will be mention below.

The systems which have issued concerning probability can be reduced to three heads, namely tutiorism, probabiliorism and probabilism. — There can be added a certain system lately arisen under the name of compensative probabilism.

1° Rigid or absolute tutiorists are those who, in the conflict of two opinions whereof one favors the law and the other liberty, will that the side of the law always be embraced, professing this principle: « In doubt the safer side is to be followed. » From this doctrine it follows that even a most probable opinion favoring liberty cannot safely, that is licitly, in practice be preferred. And in truth many of the Jansenian sect, with Nicolaus for leader, required in every case moral certainty of the honesty of the action, that conscience be unhurt. But when Alexander VIII had condemned the following proposition: « It is not licit to follow the opinion, even though most probable among probables, » several, withdrawing from their pristine rigor that they might avoid the pontifical censure, conceded it licit to follow an opinion against the law provided it be most probable, because then the action is most probably honest, and as such opposed to no rules of prudence. These later tutiorists are called benign.

2° Probabiliorists hold it licit to follow the less safe opinion, provided it be truly, that is notably, more probable. If the opinion favoring liberty be only lightly more probable, they permit it not to be preferred, because, say they, in morals little is reputed as nothing. Of the truth of this system our Billuart above endeavored to give demonstration.

3° Probabilists teach it licit to follow the less safe opinion although it be not notably more probable. They are divided into three classes: 1° Rigid probabilists, or equiprobabilists, assert that election is not free unless the opinions for the law and against the law be equally probable. 2° Benign or moderate probabilists hold it licit to follow the opinion less safe and less probable, provided it be truly and solidly probable. 3° Lax or laxer probabilists taught that it is ever lawful to follow the opinion less safe and probable, even should its probability be slight or most slight, « provided one go not beyond the bounds of probability ». This system was condemned, as will plainly appear below.

4° The system of compensative probabilism, which will be set forth more fully below, consists in this. Since the law is doubtful, or existing only probably, if such a law binds, in favor of liberty it is not licit to solve the doubt, unless first the advantages and disadvantages which must arise have been pondered and weighed, whether one act according to the law or against it. If the advantages which the agent acting against the law will enjoy surpass, or at least equal, the inconveniences thence arising, it is licit to use liberty; otherwise the law prevails. — This pseudo-probabilism will be weighed in its own place, and we shall demonstrate its emptiness, the question of probabilism being first exhausted, to which truly it does not belong.

The various systems opposed to moderate probabilism will sufficiently be overthrown by the demonstration of the proposition which enunciates the whole doctrine of the probabilists. Whence