456. As to the effects of ignorance on acts irritated by law, the Code states that ignorance of irritating (invalidating) and inhabilitating (disqualifying) laws does not excuse from their observance, unless the law expressly states otherwise (Canon 16, Sec. 1). Moralists discuss the influence of ignorance (as well as force or fear) on such acts as follows: (a) if the law is irritant and not penal, it has its effect, in spite of ignorance, oversight, etc.; for this the common good requires. Example: One who marries his cousin in good faith, being invincibly ignorant that it is against the law, contracts invalidly; (b) if the law is irritant and penal, the irritation being decreed solely as a punishment, ignorance, oversight, etc., sufficient to excuse from fault, excuse also from the penalty of irritation; for penalty presupposes fault. Before the law, however, ignorance and error as to law or penalties are not presumed but must be proved. (Nevertheless, it must be noted that according to some authors no penalty is necessarily or primarily intended in ecclesiastical irritating and inhabilitating laws. Though punishment actually results from the matrimonial impediment of crime, for example, the impediment as such primarily is a personal disqualification intended to protect the dignity of the sacrament and good morals. Ignorance, then, does not excuse from it. Some authors maintain that this is true of all ecclesiastical disqualifying laws.)
457. Generally speaking, _epieikeia_ may not be used in the interpretation of irritating and inhabilitating laws. Since they transcend the individual welfare, they demand uniform observance of all subject to them. Some authors permit the use of _epieikeia_, however, in particular cases in which the law itself aims to protect the individual, whereas its observance would tend rather to harm the individual or at times even the interests of the community. Accordingly, it seems probable that an irritant law may cease in case of impossibility or of a most grave inconvenience that is common. Example: If in a pagan country Christians were so few that they could marry only infidels, and if distance or other circumstances made it impossible to seek a dispensation, the diriment impediment of disparity of worship would seem to cease for those Christians.
458. Some authors hold that an irritant law may also cease on account of impossibility, or of a most grave inconvenience that is only private; but this opinion cannot be deemed certain. An example of private inconvenience is the case of an invalidly married person who is near to death and unable to seek the dispensation from the impediment that has made the marriage null.
459. A law based on presumption is one in which the lawgiver rules for certain cases according to what experience shows in their regard—viz., that such cases are generally dangerous, or indicative of a particular fact. These laws are not of uncertain force, for the cases in which they cease to oblige are few and definite.
460. When a law is based on a presumption of common danger and that danger does not exist in a particular instance, the law nevertheless obliges (Canon 21); for the end of the law is the common good, and if it ceased for an individual whenever its presumption of danger was not true in his case, everyone could persuade himself that the law did not apply to him, and thus the common good would be defeated. Examples: The law against the reading of irreligious books is based on the presumption of common danger of sin, the law against clandestine marriages on the presumption of common danger of fraud; hence, they oblige even in the particular instances where these dangers are absent. Examples of laws based on the presumption of common danger can be found in Canons 199; 409, Sec. 1; 420; 422; 1022; 1028; 1114; 1116; 1138; 1396; 1398.
461. When a law is based on the presumption of a particular fact that usually happens in the cases with which the law is concerned, and the fact in an individual instance did not happen, does the law oblige?
(a) In conscience the law does not oblige of itself, because presumptions must yield to the truth; but it may oblige accidentally, if non-observance would cause great public or private harm. Example: The law presumes that a person born and brought up among Catholics has been baptized, and is therefore subject to the church laws. But if, in fact, the person was never baptized, he is not subject to those laws, as long as he remains unbaptized, unless there be some accidental necessity of keeping them, such as the danger of scandal.
(b) Before the public authority the law in question does oblige until the non-existence of the fact presumed by the law has been proved in the manner required by law. Example: When parties contract marriage according to the form prescribed by the Church, the presumption is that the contract was valid, and, as long as that presumption is not overcome, the Church will not sanction a new marriage by either of the parties. But if it can be proved in court that threats or violence produced lack of consent, the obligation not to contract a new marriage will terminate before the law.
462. Fulfillment of Law.—With reference to the manner of fulfilling a law there are a number of questions to be considered: (a) as to the external acts, whether or not one can fulfill the law for another, whether or not the omission of some slight detail renders compliance insufficient, whether or not he who cannot fulfill the whole law is bound to fulfill a part of it, whether or not several obligations can be satisfied at the same time or by the same act, etc.; (b) as to the internal acts, whether or not one must have the intention of meeting the wishes of the lawgiver, whether or not one must be in the state of grace, etc.
463. Personal fulfillment is not always necessary; for an affirmative law requires either that some thing be given, or that some personal act be performed. (a) When the law requires that some thing be given (e.g., that taxes be paid), the obligation can be satisfied through another, since a thing can be transferred from one person to another, who agrees at least interpretatively; (b) when the law requires that a personal act be performed (e.g., that Mass be heard on Sunday), the obligation cannot be satisfied through another, for actions cannot be transferred from one to another.