§ 1. On Certain Conscience.

218. Notion and division. Certain conscience is that by which the mind firmly judges, without fear of erring, that an action is good and licit or evil and illicit.

a. By reason of the motive, strict or perfect certitude is distinguished, which wholly excludes every doubt and every fear of erring, even an imprudent fear; and broad or imperfect certitude, which excludes only every prudent doubt, yet rests upon motives of such a kind as truly merit assent excluding prudent fear of erring.

Broad or imperfect certitude is customarily called moral certitude. This must suffice for us in many matters even of the highest moment, because in these matters we cannot have a greater and more perfect certitude, e.g. concerning the validity of baptism or priestly ordination. Nevertheless it must not be confused with moral certitude which is improperly called by this name and signifies nothing other than a certain greater degree of probability, which nevertheless does not exceed the limits of probability.

b. By reason of the object, speculative certitude is distinguished, which is concerned with abstract truths or with the liceity of an action in general, e.g. to plow is a servile work, or servile works are prohibited on a feast day; and practical certitude, which is concerned with the liceity of an action to be placed here and now, e.g. today, even if it is a feast day, it is lawful for me to paint.

c. By reason of the mode in which it is acquired, direct and indirect or reflex certitude is distinguished. Direct certitude is called that which arises from the internal principles of reason, which demonstrate the truth of the matter itself and the honesty of the action; indirect certitude is called that which arises from external (reflex) principles, which do not demonstrate the truth of the matter itself and the honesty of the action, but from which nevertheless the honesty of the action is certainly gathered.

Let the example be a judge who must condemn the guilty and absolve the innocent. Now if from the judicial acts the accused is demonstrated guilty, the judge has direct certitude of the crime committed and forms a directly certain dictate of conscience: this accused person must be condemned by me. But if from the judicial acts grave reasons show the accused guilty, but other grave reasons show him innocent, he does not acquire direct certitude concerning the committed crime and a directly certain dictate concerning the accused to be condemned or absolved; but by applying this reflex principle: in doubt favor is to be shown to the accused, he forms an indirectly certain dictate: this accused person must be absolved by me.

219. Principles. 1. Certain conscience alone is the right norm of our actions: for from the Apostle, everything which is not from faith, i.e. which is not from certain persuasion that the thing which is done is honest and licit, is sin.¹ Certainly, he who operates with a conscience which is not certain voluntarily exposes himself to the danger of transgressing the divine will; but one acting thus virtually consents to the transgression of the precept, and therefore sins formally. Wherefore it is never lawful to act without certain conscience concerning the honesty of the action.

2. In order that we may follow conscience, it suffices that it be morally certain with imperfect certitude: for in our moral actions that certitude must suffice, of which the very nature of things does not admit a greater; but moral matters for the most part admit no certitude other than moral or broad certitude. Besides, for operating licitly a truly certain persuasion concerning the honesty of the action suffices; but morally certain conscience is truly certain.

A negative doubt does not impede the certitude of conscience, because it is founded either upon no reason or only upon a lighter and empty reason and is known as such by the agent. Therefore he who acts with a doubt of this kind nevertheless has a practically certain conscience. From this it is clear that negative doubt is to be spurned and only positive doubt in a moral matter is to be attended to.

3. For operating licitly any practically certain conscience suffices, even indirect conscience; for in order to operate licitly nothing else is required except certain persuasion that the action to be placed here and now is honest; but any practically certain conscience supplies this persuasion, whether by direct or reflex certitude.

¹ Rom. 14, 23.