Article III: On Custom

Note beforehand. Here the matter concerns only human law, which can be changed or taken away through custom. Against natural or divine law there cannot be given custom. Yet divine law, as regards the extension of the object, will be able to be more explained through custom: for example, as regards the accusation of external sins.

261. DEFINITION. Custom is either of fact or of right. Custom of fact, or material custom, is frequency of similar acts of some community. Custom of right, or formal custom, concerning which we here treat, is customarily defined: Unwritten right, induced by long-standing morals of the people, with some consent of the legislator.

DIVISION. Custom is either according to, beyond, or against law.

1. Custom according to law is that which is conformable to pre-existing law. Such custom confirms or interprets an established law by long use (cf. n. 170).

2. Custom beyond law is that which is neither prescribed by law nor opposed to law, such as would be, for example, the custom of hearing Mass outside feast days. Such custom can induce a new right where law is lacking.

3. Custom against law is that which is opposed to law, as there are, for example, in divine offices many ceremonies which the Roman decrees do not acknowledge (cf. n. 1638). Such custom introduces a right contrary to law, either by abrogating the law, or by derogating from it, whether as regards the obligation itself, or at least as regards the penalty established by the law. "Custom can also validate a contract invalidated by law, and introduce new impediments invalidating matrimony" (I, 107), and thus we have the impediment of disparity of cult.

With these things premised, it comes to be treated: 1. concerning the conditions of legitimate custom; 2. concerning the prohibition and abrogation of custom.