Summa Theologiae Moralis, vol. I: De Principiis

S. Th. in IV Sent. d. 21, q. 2, a. 3; Quodl. VIII, q. 16, a. 13.

213. Notions. — Conscience must also be certain. Now on the ground of the subject, i.e. on the part of the act of assent or adherence to the object, conscience is either certain if its judgment adheres firmly to someone, or uncertain or opinative if it adheres but with fear of the opposite. Certain conscience, therefore, is that which formally in itself and in all the principles from which it is formed excludes the fear of the opposite, and therefore firmly and without fear of erring judges that something in particular is licit or illicit.

Now we ask whether conscience, to be the rule of acting, must be certain.

214. Principle. The legitimate rule of acting is certain conscience alone, by which namely a man prudently forms for himself a certain judgment that the action to be placed here and now is licitly and honestly placed; whence such conscience is required for lawful action.

It is proved 1° from Scripture, Rom. XIV, 23: Whatever is not from faith is sin; but he who is uncertain does not act from conviction, and therefore what is done from an uncertain conscience is not from faith or persuasion; therefore it is sin. This conclusion the Apostle explicitly posits, deducing it from the said principle: He who distinguishes (i.e. he who hesitates or doubts whether to eat some food is licit), if he eats, is condemned, because not from faith. Hence Eccli. XXXVII, 20: Before every work let the word precede thee, and before every act stable counsel.

2° by reason: a) He who acts with an uncertain conscience has a reasonable and well-founded fear of malice, and uncertainty about the goodness of his act. But he who is uncertain about the goodness of his act and nevertheless acts, wills to place it whether it be against the law or not, and thus hypothetically consents to evil, and has an evil will, and despises the law of God and acts badly. It is confirmed by the example of a servant who, doubting whether something is against his master's will, neglects to seek the master's will if he can and nevertheless acts: he would be held guilty by all. Likewise he who would do what he suspects to offend a friend, would be held by that very fact to offend him and despise his friendship.

b) He who voluntarily exposes himself to a proximate danger of formally sinning and offending God, acts badly. But he who says: it is uncertain whether in fact it is evil, and acts, acts rashly because he does what he fears may offend God, and so exposes himself to a proximate danger of formally sinning and offending God. Therefore he acts badly. Hence Augustine against the Donatists: «To receive (Baptism) in the part of Donatus,..., if it is uncertain that it is a sin, who would doubt that it is certain sin¹ ».

c) Conscience is the rule and measure of our acts. But a measure cannot be ambiguous, but must be certain. Therefore conscience must be certain.

215. Applications. — From what has been said it follows:

1. He who has no certain practical judgment about the licitness of an action, that is, no certain conscience, cannot act; and if he must absolutely act, is bound to do what is safer, i.e. what is more favorable to the law (or obligation) and more removes from the danger of acting badly. Hence the axiom: In practical doubts the safer way is to be chosen.

2. He who has no certain direct, speculative-practical judgment about the objective and material honesty of an action, does not for that reason always lack a certain practical judgment about its subjective and formal honesty, but sometimes has a certain conscience from a certain superior principle and from a reflex judgment of the intellect reflecting upon its own act and applying that principle, e. g. although the morality of such an action is doubtful to me, it is certain to me that I ought to place it if a superior commands, both because the presumption stands for the superior who therefore commands by his right, which certainly holds, and is not to be deprived of it by the doubt of subjects, and because the right order of the common good forbids that subjects deny obedience unless it certainly appears that the superior is abusing his power; — although I doubt whether such a work is servile, it is certain that I may exercise it if the parish priest has said so; — although in itself it is uncertain whether a sacrament is validly and licitly administered in such matter, it is certain to me that I ought regularly to abstain from such administration out of reverence for the sacrament, in case of necessity to employ it; — although such a man is probably guilty, it is certain that a judge cannot condemn him unless he is proved certainly guilty, etc., for there are many similar cases as determined in special treatises.

3. Specifically, a practical judgment is to be held certain, e-

in IV Sent. d. 21, q. 2, a. 3: «He who commits or omits anything in which he doubts that there is mortal sin, exposes himself to danger». Likewise in Scotus, q. 2, prol., and in IV Sent. d. 30, q. 1, i; and in S. Alphonsus Th. M., l. 1, n. 22.

ven if a speculative doubt remains, and a certain conscience of a special obligation arises, whenever there is a certain and absolute obligation of obtaining a determinate end which otherwise perhaps would not be obtained, e.g. whenever a good effect (e.g. salvation, sacrament, health) is absolutely to be obtained, or an evil (harm, death, damage) absolutely to be avoided, and doubt exists not only about the honesty but also about the necessity or efficacy of the means² required for this and about the validity of the act or deed. Then namely there intervenes a certain superior law which dictates in doubts about the validity of the act to be placed that it is safer to act. From which reflex judgment an objectively uncertain obligation becomes subjectively certain. The reason is, because if the honesty of an action depends on our reason and conscience, the value of the action or the averting of harm does not so depend, for our doubt or judgment cannot change the nature of things, nor therefore render an invalid act valid, or cause that the due effect arises from the action, or prevent harm from following it; e.g. a doubt or opinion however probable cannot effect that what is not a sacrament becomes a sacrament, or that what is rather poison becomes medicine. Hence in this case the certain natural law forbids exposing oneself to the danger of not obtaining the end or of bringing harm, by employing namely a means that is perhaps inefficacious or harmful. To expose oneself to danger of this kind, specifically, is most illicit, in doubts about those things necessary by necessity of means for eternal salvation: in these namely the safer and more certain course is to be followed.

4. He who is uncertain, not indeed about the value of the act or the necessity of means, but about its mere honesty or mere necessity of precept, must, before he can act, lay aside his doubt either by more diligently inquiring into the truth or by consulting the more learned, and form for himself a certain conscience about the honesty of the action, at least indirectly from a reflex judgment applying some certain general principle. How this can be done in various cases and doubts, all circumstances being considered, prudence teaches, and therefore it will be explained in the treatise on prudence. But if such means are lacking here and now, he must abstain from action; or if he cannot absolutely suspend it, he must choose what is safer, as has been said above, in 1).