Medieval judicial torture could be ordered only on a standing half-proof, and functioned to produce the confession that completed it into full proof

In the Roman-canon law of proofs, a single eyewitness or a single private document counted only as a semiplena probatio — a half-proof, short of the two witnesses or confession that alone made "full proof" (claim-roman-canon-law-rated-one-witness-equal-to-a-private-document). Judicial torture was wired into the gap between the two. It was not a free-standing power: it was licensed only once a half-proof already stood against the accused, and its purpose was to extract the confession that would complete the arithmetic. James Franklin states the rule directly — torture "could be applied only when there was half-proof of guilt (to produce the other half)" — and the threshold recurs in the secondary literature: James Whitman (p. 115, via Karnavas) writes that "the torture could not be ordered unless there was 'semiplena probatio' or 'half-full proof,'" and John Langbein's account holds that the two-witness/confession system "was unworkable standing alone," so torture "extended" it.

This is the load-bearing dark side of the fractional-proof regime: a legal system that had legislated evidence into fixed fractions then built coercion into the sum, making torture the licensed instrument of completion rather than an aberration. The mechanism was previously carried in the vault only as a Tier-3 corollary on an encyclopedia paraphrase; this note records the newer, stronger corroboration (Franklin as a Tier-1 published chapter; Whitman and Langbein as named secondaries) while preserving the standing verification gap — see question-verify-half-proof-torture-completion-mechanism, which still awaits a direct read of Langbein's Torture and the Law of Proof or a medieval primary.