of the legislator, of the second to spread the knowledge of legislative enactments among subjects bound to observe them. Revocation The act of recalling or annulling, the reversal of an act, the recalling of a grant, or the making void of some deed previously existing. This term is of wide application in canon law. Grants, laws, contracts, sentences, jurisdiction, appointments are at times revoked by the grantor, his successor or superior according to the prescriptions of law. Revocation without just cause is illicit, though often valid. Laws and customs are revoked when, owing to change of circumstances, they cease to be just and reasonable. Concordats (q.v.) are revocable when they redound to the serious injury of the Church. Minors and ecclesiastical institutions may have sentences in certain civil trials set aside (Restitutio in integrum). Contracts by which ecclesiastical property is alienated are sometimes rescindable. A judge may revoke his own interlocutory sentence but not a definitive judicial sentence. Many appointments are revocable at will; others require a judicial trial or other formalities. Vacatio legis In principle, a law becomes binding from the time of its promulgation. But because there are often reasons that the immediate efficacy of a law would be detrimental to those upon whom it enjoins, the legislator often orders a delay—vacatio—in the law's applicability. In Latin canon law, the vacatio legis is three calendar months after promulgation for universal laws, and one calendar month after promulgation for particular laws, unless the law itself establishes a longer or shorter period of time. The legislator of the law can stipulate a longer or shorter time of vacatio than that which is stipulated generally. Valid but illicit The term "valid but illicit" (or "valid but illegal") refers to an unauthorized celebration of a sacrament or the placement of a juridic act which does not follow non-essential things commanded by the law, but that nevertheless has effect. While validity is presumed whenever an act is placed "by a qualified person and includes those things which essentially constitute the act itself as well as the formalities and requirements imposed by law for the validity of the act", Roman Catholic canon law also lays down rules for lawful placing of the act. Principles of legal interpretation Canonists have formulated interpretive rules for the proper interpretation of canonical laws. An authentic interpretation is an official interpretation of a statute issued by the statute's legislator.