Nemo judex in causa sua (or
nemo judex in sua causa) is a
Latin phrase that means, literally, no-one should be a judge in his own cause. It is a principle of
natural justice that no person can judge a case in which they have an interest. The rule is very strictly applied to any appearance of a possible bias, even if there is actually none: "Justice must not only be done, but must be seen to be done".