(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). 508. Custom is formed as follows. (a) As to origin, it arises from the practice of the people, when this practice is followed with the purpose of making or unmaking a law. Hence, the habitual way of acting of an individual, even if he be the superior, does not give rise to a custom. By “people” here is meant a community capable of having its own law (Canon 26). (b) As to legal force, custom arises solely from the consent of the Pope or other prelate, when this consent is expressed by the law or lawgiver, or tacitly admitted by him. Hence, a custom not approved by the superior has no legal force (Canon 25). 509. A custom can introduce or abrogate any kind of ecclesiastical law or other custom--penal, prohibitive, irritant--if it is reasonable and has lasted the prescribed time (Canons 27, 28). Examples: A law that forbids contrary customs can be abrogated, according to the Code, by such customs when they are immemorial, or a century old (Canon 27, Sec. 1). The impediment of disparity of worship became diriment through custom; it was custom that introduced the obligation of the Divine Office, and that mitigated the early law of fast.