Half-proof

Half-proof (semiplena probatio) was a concept of medieval Roman law, describing a level of evidence between mere suspicion and the full proof (plena probatio) 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.[1]: 26–27, 59 

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.[2]

However, the concept never became firmly established in English law.

Voltaire claimed that the Parlement of Toulouse dealt not only in half-proofs but in quarter-proofs and eighth-proofs,[3] but there is no direct evidence of that.

In later times, half-proof was mentioned in 19th century Scots law[4] and in the 1917 Catholic Code of Canon Law.[1]: 369 

  1. ^ a b c Franklin, James (2001). The Science of Conjecture: Evidence and Probability Before Pascal. Baltimore: Johns Hopkins University Press. p. 18-19. ISBN 0-8018-6569-7.
  2. ^ B. Shapiro, Probability and Certainty in Seventeenth-Century England, Princeton, 1983, p. 180.
  3. ^ Beccaria, Cesare; Voltaire, François-Marie Arouet (1872). "XXII". An Essay on Crimes and Punishments. By the Marquis Beccaria of Milan. With a Commentary by M. de Voltaire. Albany, NY: W.C. Little.
  4. ^ J. Erskine, An Institute of the Law of Scotland, ed. J. Ivory, Edinburgh, 1828, II: pp. 965, 972.