Nemo iudex in causa sua

Nemo judex in causa sua (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 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".