(b) The law becomes harmful or useless with reference to the lawgiver’s purpose privately or temporarily, if the harm or uselessness affects only individuals, or is not lasting. In this case the law continues to be an instrument of public welfare, or is only momentarily deprived of its beneficial character. Hence it endures; but for temporary inconvenience to the public a remedy is had in suspension of the law, for inconvenience to individuals in dispensation. Example: If the use of fats or grease were forbidden on days of abstinence, and if for a time only it were impossible to obtain the substitutes for the preparation of the food, the law would not cease, but would be suspended until such time as substitutes could be obtained.
503. The inconvenience caused to individuals from the fact that a law does not serve its purpose in a case before them, does not always justify the use of _epieikeia_.
(a) If the observance of the law would be detrimental to the purpose intended by the lawgiver, _epieikeia_ might be used; for the lawgiver does not intend that his law should be an obstacle to what he has in view as its end. Example: Caius needs to read a book placed on the Index in order to defend the Faith against attacks, but he is unable to request the general faculty to read forbidden works. Obedience to the law in this case would defeat the purpose of the law, which is the protection of faith, and hence Caius may use epieikeia.
(b) If the observance of the law would be unnecessary, but not detrimental as regards the purpose of the lawgiver, _epieikeia_ may not be used; else the law would lose its force through the judgments of individuals in their own favor, and the common welfare would suffer. Examples: Titus has an opportunity to read a book placed on the Index, but has not the time to apply for permission. The work was condemned as dangerous to faith; but Titus is strong in faith, and wishes only to study the literary qualities of the writer. Sempronius, a parish priest, is requested to officiate at a marriage immediately, without proclaiming the banns or seeking a dispensation from proclamation. The purpose of the law of banns is that impediments may be detected and invalid marriages avoided, and Sempronius is absolutely certain that there is no impediment in the case before him. Titus and Sempronius must observe the law, and the same must be said as regards every actual case in which there is the possibility of self-deception and peril to the common good. The theoretical case, in which neither of these inconveniences would be present, need not be considered.
504. The purpose of the law ceases to exist as follows:
(a) adequately, when all the reasons on account of which it was made are no longer in existence; in such a case the law itself ceases, for the lawgiver is not considered as intending to oblige when the reason for obligation has ceased. Example: If the bishop orders prayers to be said for rain, the prayers cease to be obligatory when rain has come;
(b) inadequately, when the reason for the law has ceased partially, but not entirely. In such a case the law does not cease, for it still remains useful. Example: If the bishop orders prayers for peace and rain, the prayers are obligatory until both requests have been obtained.
505. A law ceases, therefore, in greater or less degree, according to circumstances. (a) It ceases entirely or partially, according as it is revoked or as it becomes useless as to all its provisions, or only as to one or more of them; (b) it ceases permanently or temporarily, according as the revocation or cessation is only for a time, or for good.
506. Custom.—In Canon Law custom can interpret, abrogate or introduce law, provided: (a) it has the qualities of legitimate custom, and (b) its existence is proved juridically, or is notorious.
507. According to their extension, customs are of various kinds. (a) Universal customs are those that prevail in the entire Church; (b) particular customs are those that are confined to a territorial portion of the Church (e.g., a province of the Church or of an Order); (c) special customs are those that are followed in societies that are smaller, but capable of having their own laws (e.g., independent monasteries); (d) most special customs are those observed by individuals, or by communities not capable of having their own legislation (e.g., parishes). At the most, customs of this last class have only the force of privilege (Canon 26).