Nemo iudex in causa sua

Nemo judex in causa sua (IPA: [ˈne.mo ˈju.dɛks in ˈkau̯.sa ˈsua]; also written as nemo [est] judex in sua causa, in propria causa, in re sua or in parte sua) is a Latin brocard that translates as "no one is judge in his 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. However, William Blackstone deemed such principles too bold unless alterable by legislative power.

History

The Latin brocard nemo judex in causa sua 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" (neminem sibi esse iudicem vel ius sibi dicere debere) (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" (iniquum est aliquem suae rei iudicem fieri) (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 (Niemand sol sein selbs Richter seyn, 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 aliquis non debet esse iudex in propria causa".