451. An irritant or inhabilitating law is one that expressly or equivalently declares that certain defects make an act void or voidable, or a person incapable. Such laws are just, even when made by human authority, since it is the common good that makes them necessary, and the natural law itself requires that the common good be promoted.
452. Irritant laws are of various kinds.
(a) They are morally or juridically irritant, according as that which is taken from the irritated act is either the natural value it has in conscience, or the positive value it derives from the law. Hence, an act may be legally null (i.e., have no value that the law recognizes or protects) and at the same time morally valid (i.e., of just as much force in conscience as though no irritant law existed).
(b) Irritant laws are merely irritant or irritant and prohibitive, according as they make an act invalid but not illicit, or both invalid and illicit. Thus, a law that requires certain formalities for making a will invalidates the act of writing an informal will, but does not make it an offense; but the church law of diriment impediments makes a marriage contracted with one of these impediments both null and sinful.
(c) Irritant laws are merely irritant or irritant and penal, according as the legislator does not or does intend them as punishments. For example, the law of clandestinity is merely irritant; the law regarding the impediment of crime is probably both irritant and penal.
453. Laws that are merely irritant do not oblige one in conscience to omit the act, but only to suffer the effect of irritation; but laws that are both irritant and prohibitive oblige one in conscience to omit the act. Example: In itself, it is not unlawful to make an informal will, but it is unlawful to marry with a diriment impediment.
454. As to the time when irritant laws obtain their effect, the following points are important.
(a) Ecclesiastical voiding laws oblige at once in conscience, although like other laws of the Church they are not retroactive, unless the contrary is provided, and they do not oblige in case of a doubt concerning the law. Example: If espousals are made without the canonical formalities, there is no duty to live up to them as such, either in conscience or before the law.
(b) Civil voiding laws are generally only civilly irritant, for as a rule external means are sufficient for the purpose of those laws; thus, they produce civil irritation at once, but moral irritation only after pronouncement by the courts. Hence, after a judicial sentence the voided act becomes such morally, since the decision is founded on a presumption of common danger (see below, 459). Examples: One who has received money through a will which he knows to be informal (i.e., legally invalid), may retain possession until the civil authority declares that he has no rights to the money. But, on the other hand, one who has been disinherited through a will naturally good, but not made in due form, has the right to contest, if we except the case of pious bequests (see Vol. II).
455. Laws that make an act voidable or rescindable do not irritate before declaration of nullity by a judge. Hence, an act that is rescindable according to law retains its natural force until the court has decided against it. Example: Acts that were done under the influence of grave and unjust fear, or that were induced through deception, are held as valid until declared null by a judge.