Some Rules for Discerning Sin with a Rightly Formed Conscience

Dec 30, 2025

Jean-François of Reims:

The third rule that those with a properly formed conscience must observe in order to know when there is sin in a thing is this: there is never sin in any action, word, or thought, that the will embraces or omits, before the understanding and conscience have specifically indicated to it that the thing is a sin, and that there is wrongdoing in undertaking it.

The reason is that every action, word, thought, or omission, in order to be a sin, must be voluntary insofar as it is a sin; that is to say, it must be embraced by the will, enlightened by the understanding, as a sin. For the will does not sin insofar as it is directed precisely toward an object that is intrinsically such, but insofar as it is directed toward an object that the understanding has represented to it as evil.

Now, the will, which is a blind power, cannot embrace any object as a sin if the understanding does not currently recognize the malice of the object, and without this actual knowledge, it cannot be said to be voluntary insofar as it is a sin. It may indeed be voluntary under some other consideration, insofar as the will freely moves to embrace it, but not insofar as it is a sin, because knowledge of the malice has not intervened…

Good souls can draw several instructions from this doctrine for the rest of their conscience.

First, when they have performed some action in good faith, without thinking there was any evil in it, and later come to realize that it is not good in itself, they must believe that they have committed no sin, since ignorance or inadvertence excuses them from all sin, and makes the action not freely willed as a sin. Except if the ignorance was gross and somewhat voluntary (that is, if they notably neglected to learn what it was their duty to know) or affected (that is, if they did not wish at all to learn what they were obliged to know), which does not happen to people who fear God.

Second, when they have directed themselves toward some bad action, or lingered on some illicit thought for even a long time, although they had habitual knowledge that this action or thought was evil and not permitted to them, nevertheless they did not recognize the malice of this action or thought at the moment they actually engaged in it, and had no awareness that it involved sin; in this case, they must believe that they have not committed sin.

Third, when they have done an action, or dwelled on an illicit thought, with some imperfect and confused knowledge of the malice of this action or thought (as when they were driven by some violent passion, or were half-asleep, so that the understanding was clouded and could not clearly recognize the malice of this action or thought), they must be assured that they have at least not committed mortal sin, since to commit mortal sin requires full freedom of the will, which presupposes perfect knowledge in the understanding.

I could here be accused of repeating what I have already said elsewhere concerning this third rule, but having spoken briefly before, I thought it necessary to explain it here more clearly and fully, due to its usefulness.

The fourth rule that those with a rightly-formed conscience should use is that when a thing presents itself to be done or avoided, they may form their conscience either on some probable opinion (for example, an opinion they know comes from a learned and pious person), or on some reason they believe in conscience to be good, and such that it would not make them doubt the contrary; or else on what people who fear God do without difficulty. If reasons or opinions arise on both sides, which they know to be probable, they may choose whichever they wish. As for doubts that leave them suspended as to whether a thing is lawful or unlawful, they must seek clarification and follow the resolution given by a learned person.

The last rule they must observe is that when they fail to do something commanded, they are at least excused from mortal sin if, in good faith and without contempt, they believe, for some good reason, that they are excused from sin in omitting it, with the virtual will that they would not omit it if they knew it involved mortal sin. And one should not object that one puts oneself in danger of committing mortal sin by acting in this way, for it is not putting oneself in danger when one follows a reason that one sincerely believes to be good and sufficient to exempt from mortal sin.