Nemo iudex in causa sua

Nemo judex in causa sua (also written as , , or ) is a Latin brocard that translates as "no one is judge in their own case". Originating from Roman law, it was crystallized into a phrase by Edward Coke in the 17th century and is now widely regarded as a fundamental tenet of natural justice and constitutionalism. It states that no one can judge a case in which they have an interest. In some jurisdictions, the principle is strictly enforced to avoid any appearance of bias, even when there is none: as Lord Chief Justice Hewart laid down in Rex v. Sussex Justices, "Justice must not only be done, but must also be seen to be done". History The Latin brocard has its origins in the Roman legal tradition and is codified within the Corpus Juris Civilis. In 376 AD, an imperial decree established the principle that "no one shall decide his own case or interpret the law for himself" () (Code 3.5.1). Additionally, the Digest records Julianus's statement that "it is unfair for someone to be the judge of their own affairs" () (Digest 5.1.15-17). From these Roman sources, the principle has endured into modern times and can be traced in Martin Luther's 1526 work Whether Soldiers, Too, Can Be Saved (, meaning "no one should be their own judge"), in Ulrich Zwingli's In Exodum (1527) in Jean Bodin's The Six Books of the Republic (1576) and in Hobbes's Leviathan (1651) ("And seeing every man is presumed to do all things in order to his own benefit, no man is a fit Arbitrator in his own cause"). In the 17th century, the English jurist Edward Coke turned the idea into a phrase when he wrote that "it is a maxim in law ". Coke used the principle to instruct the king that he could not personally judge a dispute between himself and his subject. Moreover, In the famous Bonham's Case of 1610 Coke ruled that the College of Physicians could not sit as judges in a case to which they were a party, and he was understood also to have affirmed that that the principle could not be overridden by statutory provision.