Section — Wouters, Manual of Moral Theology
Scholion I. On the Obligation of the Faithful
I. All the faithful are bound to reveal impediments, if they know any, to the pastor or Ordinary before the celebration of matrimony (canon 1027); this obligation, as is drawn from the nature of the thing prescribed, is of itself grave. It is said:
If they know any, that is, if they have certain or probable knowledge of a diriment or prohibitive impediment. Therefore one is not bound who heard the matter from a person not worthy of trust, unless there is hope of further detecting the truth (St. Alphonsus VI, 994).
They are bound to reveal impediments before the celebration of matrimony to the pastor or local Ordinary. But one who warns those about to marry that a dispensation must be sought or that matrimony must not be entered, foreseeing that the warning will be beneficial, satisfies the obligation. Indeed, if it is a question of an infamous impediment, he must first give the aforesaid warning, unless hope of fruit is lacking, or another cause excusing from the warning is present (St. Alphonsus, ibid.).
II. The following are excused from the obligation set forth:
One who knows that a dispensation has been obtained or sought, or at least will be sought.
One who cannot reveal the impediment without grave inconvenience to himself or his own, or to the community, is excused from the burden of revelation, although he can be bound to warn those about to marry.
One who knows an impediment under secrecy is excused thus:
a) If the secret is natural or promised, he is not excused, because the reverence due to the sacrament and the avoidance of evils arising from invalid matrimony prevail over the obligation annexed of itself to the said secrets. And this holds even if an oath has been added (St. Alphonsus VI, 994).
b) If the secret is committed, and it is a question of one who is not bound by force of office to keep the secret, he is not excused for the reason given above. But one who by force of office is bound to keep the secret is excused, because the common good, to which it is of the highest interest that such a secret be kept, prevails over the reverence of itself due to the sacrament and over the avoidance of the evils which are annexed to invalid matrimony.