Half-proof (semiplena probatio), was a concept of medieval Roman law, describing a level of evidence between mere suspicion and the full proof needed to convict someone of a crime. The concept was introduced by the Glossators of the 1190s such as Azo, who gives such examples as a single witness or private documents.[1]
In cases where there was half-proof against a defendant, he might be allowed to take an oath as to his innocence, or he might be sent for torture to extract further evidence that could complete the burden of proof.[2]
Sir Matthew Hale, the leading late 17th century English jurist, wrote: "The evidence at Law which taken singly or apart makes but an imperfect proof, semiplena probatio, yet in conjunction with others grows to a full proof, like Silurus his twigs, that were easily broken apart, but in conjunction or union were not to be broken."[3] However, the concept never became firmly established in English law.
In later times, half-proof was mentioned in 19th century Scots law[4] and in the 1917 Catholic Code of Canon Law.[5]