498. It is lawful to cause impossibility of observing a law, if there be some sufficient reason for doing this; for it is lawful to do something from which two effects, one good and the other bad, result, if the good effect is the one intended, and there is a sufficient reason for permitting the evil effect (102 sqq.). Example: It is sometimes lawful to do some extra work that is very useful, even if the labor makes one unable to observe a fast.
499. The sufficient reason spoken of in the last paragraph is one that is proportionate to the urgency and importance of the command and to the frequency of the non-observance. Examples: A greater reason is required to take up some work which will make it impossible to keep the fast, if this be done on the fast day itself, than if it be done the day before. A far greater reason is required to take up some work that makes the observance of the fast impossible, if this happens frequently or habitually, than if it happens only once or twice.
500. Cessation of Law.—A law ceases in two ways.
(a) It ceases from without (i.e., from the act of the legislator), when he abolishes it, by total or partial revocation (abrogation, derogation), or by the institution of a new law directly contrary to it (obrogation). In the new Code of Canon Law there are many instances of revocation or obrogation of older legislation (see Canons 22, 23), as in the matter of censures and matrimonial impediments. Examples: In the diocese of X a minor feast was made a holyday of obligation. This law was abrogated, if later on it was decreed that neither the prohibition against servile works nor the precept of hearing Mass was obligatory for that feast; it was derogated from, if later it was decreed that servile works were permitted, but Mass was obligatory for that day; it was obrogated, if a later law included the minor feast in a list of special days of devotion for which the hearing of Mass was recommended.
(b) A law ceases from within (i.e., of itself), when through change of conditions the purpose for which it was made no longer exists, or is no longer served by the law.
501. The purpose for which a law was made ceases to be served by the law in two cases.
(a) A law no longer serves its purpose, if, from having been a benefit, it has become a detriment, inasmuch as its observance now would be wicked, or impossible, or too burdensome. In this case the law ceases, since it is now contrary to the supreme law that the common welfare be promoted. Example: A particular law forbade the use of fat or grease in the preparation of food on days of abstinence. Later, it became impossible to procure the substitutes previously used.
(b) A law no longer serves its purpose, if, from having been useful, it has become useless, inasmuch as it is no longer necessary for the end intended by the lawgiver. In this case the law ceases, for regulations should not be imposed needlessly. Example: The Council of Jerusalem made a law that the faithful should abstain from using as food animals that had been strangled (Acts, xv. 20). The purpose of the law was to avoid offense to the Jewish converts, who at that time formed a large part of the Christian community and who had a religious abhorrence for such food. But shortly afterwards, the Gentile element having become stronger in the Church, no attention was paid to ceremonial rules of Judaism.
502. A law ceases to serve its purpose also as follows:
(a) The law becomes harmful or useless with reference to the purpose of the lawgiver generally and permanently, if the changed conditions affect the whole community or the great majority, and are lasting. In this case the law ceases; for, since it is made for the community as a whole and as a lasting ordinance, it cannot endure, if it becomes permanently unserviceable to the community. Examples are given in the previous paragraph.