Other sources include apostolic constitutions, motibus propriis, particular law, and—with the approbation of the competent legislator—custom. A law must be promulgated for it to have legal effect. A later and contrary law obrogates an earlier law. Canonists have formulated interpretive rules of law for the magisterial (non-legislatorial) interpretation of canon laws. An authentic interpretation is an official interpretation of a law issued by the law's legislator, and has the force of law. Philosophy, theology, and fundamental theory of Catholic canon law Although canonical jurisprudential theory generally follows the principles of Aristotelian-Thomistic legal philosophy, Thomas Aquinas never explicitly discusses the place of canon law in his Treatise on Law However, Aquinas himself was influenced by canon law. While many canonists apply the Thomistic definition of law (lex) to canon law without objection, some authors dispute the applicability of the Thomistic definition to canon law, arguing that its application would impoverish ecclesiology and corrupt the very supernatural end of canon law. In the decades following the Second Vatican Council, many canonists called for a more theological, rather than philosophical, conception of canon law, acknowledging the "triple relationship between theology, philosophy, and canon law". Some authors conceive of canon law as essentially theological and the discipline of canon law as a theological subdiscipline, but Msgr. Carlos José Errázuriz contends that "in a certain sense, all postconciliar canonical scholarship has shown a theological concern in the widest sense, that is, a tendency to determine more clearly the place of the juridical in the mystery of the Church." The fundamental theory of canon law is a discipline covering the basis of canon law in the very nature of the church. Fundamental theory is a newer discipline that takes as is object "the existence and nature of what is juridical in the Church of Jesus Christ." The discipline seeks to better explain the nature of law in the church and engages in theological discussions in post-conciliar Catholicism and seeks to combat "postconciliar antijuridicism". Canonistics, faculties, and institutes The academic degrees in canon law are the J.C.B. (Iuris Canonici Baccalaureatus, Bachelor of Canon Law, normally taken as a graduate degree), J.C.L. (Iuris Canonici Licentiatus, Licentiate of Canon Law) and the J.C.D. (Iuris Canonici Doctor, Doctor of Canon Law), and those with a J.C.L. or higher are usually called "canonists" or "canon lawyers". Because of its specialized nature, advanced degrees in civil law or theology are normal prerequisites