Regulæ Juris (rules of law), general rules or principles serving chiefly for the interpretation of laws. In a specific sense, however, regulae juris are certain fundamental laws in the form of axioms found in the “Corpus Juris”, eleven inserted by Gregory IX at the end of the fifth Book of Decretals, eighty-eight by Boniface VIII in the last title of Liber Sextus Decretalium. These rules are an exposition of several laws on the same subject, conclusions or deductions, rather than principles, of law drawn from constitutions and decisions, and consequently reserved to the last title of the two books mentioned, in imitation of Justinian in the “Digest” (L, 1, tit. 17). While these rules are of great importance it must be remembered that few general statements are without exception. Some of these axioms are applicable in all matters, others are confined to judicial trials, benefices, etc. As examples the following are taken from Liber Sextus: No one can be held to the impossible (6); Time does not heal what was invalid from the beginning (18); What is not allowed the defendant, is denied to the plaintiff (32); What one is not permitted to do in his own name, he may not do through another (47).
REIFFENSTUEL, Jus. Canon. (Antwerp, 1755), tr. De Regulis Juris; WERNZ, Jus Decretalium, I (Rome, 1898), n. 140; Taunton, The Law of the Church (London, 1906).
Andrew B. Meehan.