Unus testis, nullus testis

Unus testis, nullus testis (lit. 'one witness, no witness') is a Latin legal phrase describing a rule of the law of evidence. According to this rule, the uncorroborated testimony of one witness should be discounted because it is deemed to be too unreliable to establish a fact. The English equivalent of the phrase is "one man, no man".^[1]

The historical foundations of the unus testis-rule are various passages in the Old and New Testament and a constitution of emperor Constantine I of AD 334. While the applicability of this rule has generally been in decline, it is still present in contemporary Dutch criminal procedure and the canon law of the Catholic Church and similar to the ongoing requirement of corroboration in Scots law.

The rule has been criticized for impeding convictions for certain types of crimes (especially sexual assault) which often only have the perpetrator and the victim present.