Medieval Roman-canon law rated a single eyewitness and a private document as equal 'half-proofs,' each insufficient alone

From the 1190s Glossators (e.g. Azo of Bologna) onward, the medieval Roman-canon law of proofs quantified evidence into fixed fractions. A single trustworthy eyewitness or a private document each counted as a "half-proof" (semiplena probatio) — the cited entry lists both as examples of the same category, neither enough on its own. "Full proof," which alone could ground a conviction, required either two eyewitnesses to the same fact or the defendant's confession [unverified-definitional — a standard legal-history characterization (e.g. Langbein's *Torture and the Law of Proof*), carried by the capture; it does not appear in the cited Wikipedia entry].

This directly resolves the recurring question of whether testimony or documents deserve more trust: the canon-law answer was to rate both as equally weak in isolation, by definition, rather than to debate which was more reliable. The system is a striking counterpoint to two other traditions that solved how much evidence is enough differently — Mabillon's comparative document authentication (claim-mabillon-1681-founded-diplomatics-to-refute-forgery-charge) and the Anglo-American jury standard (claim-whitman-reasonable-doubt-began-as-juror-soul-protection). The graded-proof architecture here (half-proof as an intermediate short of full proof) is mirrored, unexpectedly, in the vault's own source-verification ladder — a re-read of a single mirror is capture-verified but not verified-verbatim (claim-gersick-1991-deep-structure-quotes-confirmed-verbatim); the isomorphism is argued in 2026-07-11-hop-vault-tiers-revive-legal-proof.

The rigidity had a dark corollary. Because a half-proof fell short of conviction but established strong suspicion, judicial torture reportedly existed as the licensed instrument for converting a half-proof into the "full proof" of a confession. [unverified-mechanism -- needs primary] This torture-completion mechanism is the load-bearing dark side of the system and is not yet checked against a primary legal-history source; see question-verify-half-proof-torture-completion-mechanism. The quantified-proof regime was later the explicit target of the French revolutionary standard of intime conviction ("inner conviction"), which replaced fixed fractional rules with the judge's untethered conscience (capture background — this lineage is not in the cited entry and rides on the same routed verification).