Summa summae S. Thomae, Tomus II

A probable opinion is an assent of the mind given to one side on account of a fitting motive persuading its truth, yet a fallible assent, and therefore accompanied with fear of the opposite side. Hence the probability is greater or lesser according as the motive is more or less fitting and weighty.

The motive or foundation of probability is twofold, intrinsic and extrinsic; hence also a twofold probability, intrinsic and extrinsic. The intrinsic foundation consists of reasons drawn from the very nature, properties, causes and effects of the thing, and even from the inconveniences of the opposite side. The extrinsic foundation is the authority of doctors who hold or have held this opinion; which authority, however, moves only insofar as those doctors are presumed to teach or to have taught this opinion for good reasons. Whence extrinsic probability is rather to be estimated from the merit and erudition of the doctors, and from their study and diligence in examining the matter, than from their number. That the authority of one young and modern theologian does not suffice to found an extrinsic probability is clear from this proposition condemned by Alexander VII: « If a book be that of some young and modern author, the opinion must be judged probable, provided it does not stand established that it has been rejected by the Apostolic See as improbable. »

A probable opinion can be considered in two ways, separately and comparatively with the opposite, which may be equally, less, or more probable; and according to this last consideration the present question proceeds. For we do not deny that an opinion solidly probable, considered separately, if nothing appears against it, or nothing that has not been evidently solved, can safely be chosen; because man cannot always have entire certainty in morals, and he acts prudently who acts according to weighty reasons which nothing solid overthrows.

While a probable opinion is considered in conflict with the opposite, the more the probability of the one grows, the more the probability of the opposite is diminished; and when one becomes more probable and more like the truth, the other becomes less probable and more like falsehood, so that then it ceases to be solidly and expediently probable, as being incapable of persuading the truth; because the stronger motives of the one crush out the efficacy of the motives of the opposite.

The security of an opinion consists in removal from the danger of sinning, and thus it is safer by how much it removes further from the danger of sinning: whence that opinion which stands for the law is safer; that which stands for liberty is less safe. Security and probability of opinions, therefore, differ, as you see. Probability is drawn from the appearance of truth, security from removal of the danger of sinning: whence there can be given an opinion safer though less probable, and an opinion more probable though less safe. It is plain in the common example. The opinion of St. Bonaventure, which teaches that a sinner is held to repentance immediately after his fall, is safer but less probable; the opinion of St. Thomas, who teaches the opposite, is less safe, but more probable.

I say: In the conflict of two opinions concerning the objective honesty of an action, it is not lawful to follow the less probable and less safe, leaving aside the more probable and safer¹

Omitting many proofs from Scripture, the Fathers, the Supreme Pontiffs and theologians of every school, which may be seen in our former work,

It is proved 1° from St. Thomas, who in Quodlibet VII, a. 13, says: « If he who holds several benefices falls into some doubt from the contrariety of opinions, and thus, if, while such doubt remains, he holds several benefices, he exposes himself to danger, and without doubt sins, as loving temporal gain more than his own salvation². » Which words seemed so open to Amedaeus Guimenius, author of the Apologica Casuistarum, that in his Tract. de Opin. probab., n. 6, he exclaimed: « If these things are true, woe to those who act from probable opinion! »

It is proved by many reasons: 1° He who in the conflict of opinions concerning the objective honesty of an act follows the less probable standing against the law, leaving aside the more probable standing for the law, cannot frame for himself a conscience morally certain of the honesty and formal licitness of his act, neither from direct principles nor from reflex principles. Therefore he sins. The consequence is plain from what we said above, that only a morally certain conscience is the rule of our actions; because otherwise it is to act imprudently and expose oneself to the danger of sinning formally, and consequently to sin. And thus it is commonly admitted by probabilists. — The antecedent holds also for its first part; for from a less probable principle there cannot be deduced directly and immediately a morally certain conclusion: this too the adversaries concede. The whole difficulty, therefore, lies in the second part of the antecedent. Wherefore it is proved, the second part of the antecedent: 1° The reflex principles from which the probabilists contend they can immediately frame a conscience morally certain of the formal honesty of their action, by following the opinion less probable and less safe, that is, standing for liberty against the law, are: « He who acts probably acts prudently and safely. » — « The law which is probably judged not to exist is insufficiently promulgated and invincibly unknown, and therefore does not bind in act. » — « In doubt, better is the condition of the possessor of his liberty »; and certain others of less moment, for these are the principal ones. But these principles are uncertain and at most probable. Therefore from them there cannot be drawn a certain conclusion, or framed a conscience morally certain in practice of the formal honesty of the action. — The consequence is plain; for the conclusion cannot be more certain than its principles. — Proof of the minor: All anti-probabilists deny these principles as absolutely false, and without doubt their denial is probable; for they are authors most weighty in number and authority, nor are their reasons improbable: which two things found a probable opinion. Therefore these principles are uncertain and at most probable; for if they are probably false, they are only probably true. Wherefore, if the probabilists wish their reflex principles to be certain, such that from them a morally certain conscience can be framed, they must before all else prove that all the arguments we bring against them are not only not certain, but not even probable: which when they have done, we shall gladly associate ourselves with them.

2° Everyone is bound, in controversies and difficulties arising daily, especially in matters of faith and morals, sincerely to seek the truth while it lies hidden, and to strive toward it as much as he can. This principle is most certain and is proved in many ways: 1° From that of Ecclus., XXXVII, 20: Before all works let the word of truth precede thee. 2° Because the religion of Christ is a school of truth; for he himself is the way, the truth and the life, and he testifies that he came into the world to give testimony to the truth, and that he wished to institute a religion in which true adorers would adore the Father in spirit and in truth. 3° The office of an upright man requires that he not knowingly depart from the truth of the law, which all nations seek and intend. 4° Finally, right reason dictates it, whose object is truth. — I subjoin. But he who follows what he judges more probably false and contrary to the truth of the law, most certainly neither loves nor sincerely seeks the truth, nor strives toward it as much as he can. Therefore it is not lawful to follow the less probable opinion against the law, leaving aside the more probable for the law.

3° It is not lawful to follow the less safe opinion if it is not properly, solidly and expediently probable. But the less probable opinion, in conflict with the more probable, is not properly, solidly and expediently probable. — The major the probabilists now admit. — The minor is proved: That opinion is properly, solidly and expediently probable whose motives are so weighty and solid as to suffice for obtaining the assent of a prudent and learned man: thus the probabilists define it. But the motives of the less probable opinion, in conflict with the more probable, do not suffice for obtaining the assent of a prudent and learned man, but only for instilling some fear of the opposite. Therefore. — Proof of the minor: 1° The force and efficacy of those motives is overcome and crushed by stronger motives. Therefore. 2° A prudent man cannot assent to an opinion which he judges more probably false than true; for assent is an act of the mind by which we judge something true or more like the truth. Therefore. And so, although the less probable opinion in itself, or respectively in regard to him to whom its opposite does not appear more probable, can be called properly, solidly and expediently probable, yet otherwise comparatively in regard to him to whom the opposite is more probable.

4° He who acts according to the less probable and less safe opinion, in conflict with one more probable and safer, acts imprudently. Therefore he sins. — The antecedent is proved: Either he doubts of the honesty of his act, or he does not. If he doubts, he acts imprudently while that doubt stands, as he would act imprudently who took food which he doubted was poisoned; if he does not doubt, he is far more imprudent, since he does not doubt where there is so great reason for doubting, as he would be most imprudent who did not doubt food to be poisoned, while stronger motives dictated it to be poisoned.

5° According to the most celebrated rule of law, « in doubts the safer part is to be chosen³. » But he who judges the action more probably illicit more than doubts of its honesty, as is plain from the terms. Therefore. And by this argument alone the whole controversy is absolutely decided; but this cardinal rule, which the probabilists keenly impugn, we shall establish with all its supports in the following article, and we shall shut off all the evasions of the probabilists.

Finally attend to the following propositions condemned by Innocent XI, March 2, 1679: « Speaking generally, while the question is of probability, whether intrinsic or extrinsic, however slight, provided one does not pass beyond the bounds of probability, confident we do something, we always act prudently. » It is no. 3. — Likewise: « An infidel will be excused from infidelity, not believing, led by a probable opinion. » It is no. 4. From the condemnation of which propositions these common principles of the probabilists seem condemned: « He who acts probably acts prudently⁴ »; What is probable: therefore licit⁵; and the like.

Obj.: The probabilist can frame for himself a morally certain conscience from this syllogism: He who acts as he probably judges to be licit acts prudently; for a probable opinion is that which rests upon a weighty motive, and to which a prudent man can assent. But he who follows the less probable opinion acts as he probably judges to be licit. Therefore he acts prudently.

I answer. I distinguish the major: He who acts as he probably judges to be licit acts prudently — if he does not judge it more probably illicit, pass the major; if he judges it more probably illicit, I deny the major. And in this sense distinguish the minor; I deny the consequence. For he truly is imprudent who does what he judges more probably illicit.

You will insist 1°: He who acts according to an opinion truly and solidly probable acts prudently, because he acts from a weighty and solid motive to which a prudent man can assent. But the opinion, even though less probable, in conflict with its more probable opposite, is truly and solidly probable; for it rests upon a weighty motive, nor is it contrary to Scripture, councils, or the Fathers, or evident reason. Therefore.

I answer. The major being granted, I distinguish the minor. For the less probable opinion, in conflict with its more probable opposite, is truly and solidly probable respectively in regard to him to whom the opposite does not appear more probable — grant the minor; respectively in regard to him to whom the opposite appears more probable — I deny it. For since its motives are crushed by the stronger motives of the more probable, it is not sufficient to obtain the assent of him to whom the opposite appears more probable; but that opinion only is truly, solidly and expediently probable which suffices to obtain assent, according to the probabilists themselves. See the third proof by reason.

You will insist 2°: The comparative supposes the positive. Therefore, if of two opinions one is more probable, the other is truly probable.

I answer. If probable be taken strictly and properly for that which is capable of obtaining the assent of a prudent man, I deny the supposition of the antecedent; for then the more probable is not taken comparatively but adversatively, so that the sense is: One is probable, the other is not. In which sense the Apostle spoke, I Cor., VII, 9: It is better to marry than to burn. And Susanna, Dan., XIII, 23: It is better to fall into your hands without wrongdoing than to sin in the sight of God — not that it is good to burn or to die; but because it is good not to marry and not to sin, evil to burn and to die. But if probable be taken less strictly and less properly for that which instills some fear of the opposite, then the more probable can indeed be taken comparatively, but nothing thence against us.

You will insist 3°: The less safe remains truly safe in the presence of the safer; e.g., the married state is truly safe, although religion is safer. Therefore similarly the less probable remains truly probable in the presence of the more probable.

I answer. I deny the consequence. The disparity is that greater and lesser security, especially in things pertaining to counsels and not to precepts, do not arise from contrary reasons which destroy one another, as greater and lesser probability do. Thus security in religion arises from the possibility of the commandments, likewise in the married state. But, on the contrary, the probability, e.g., of the triple contract as licit arises from the fact that society is not destroyed; the probability of the same as illicit arises from the fact that society is destroyed.

You will insist 4°: From what has been said, the less safe remains safe in the presence of the safer. But the less probable opinion is less safe. Therefore it remains safe in the presence of the more probable and safer. Therefore it is lawful to follow it.

I answer. I deny the minor. For the less probable opinion standing against the law is called less safe not comparatively but adversatively, that is, it is not safe, and the other is safe, as we said above of the less probable and the more probable.

You will insist 5°: The opinion absolutely and singly probable favoring liberty against the law is safe. But, from what has been said, safety is not destroyed by another safety. Therefore.

I answer. The antecedent being set aside, I distinguish the minor. Safety is not destroyed by another safety when security arises from elsewhere than from probability — grant the minor; if it arises from probability itself, I deny the minor and the consequence.

Other and indeed more urgent arguments drawn from the insufficient promulgation and invincible ignorance of the law, from possession of liberty, from the right of following the more benign side, etc., we shall propose and solve in the following article. Whence be it