Nemo iudex in causa sua

Nemo judex in causa sua (or nemo judex in sua causa) (which, in Latin, literally means "no-one is judge in his own cause") is a principle of natural justice that no person can judge a case in which they have an interest.[1][2] In many jurisdictions 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".[3]

This principle may also be called:

• nemo judex idoneus in propria causa est
• nemo judex in parte sua
• nemo judex in re sua
• nemo debet esse judex in propria causa
• in propria causa nemo judex

The legal effect of a breach of natural justice is normally to stop the proceedings and render any judgment invalid; it should be quashed or appealed, but may be remitted for a valid re-hearing.

The phrase is credited to Sir Edward Coke in the seventeenth century,[4] but has also been attested as early as 1544.[5] It appears in Arnett v. Kennedy, 416 U.S. 134, 197 (1974) ("we might start with a first principle: '[N]o man shall be a judge in his own cause.' Bonham's Case, 8 Co. 114a, 118a, 77 Eng. Rep. 646, 652 (1610)").