---
title: "Two half-proofs on the same point could combine into full proof — except in grave criminal cases, where proof had to be 'clearer than the noonday sun'"
type: "claim"
status: "seedling"
writer_model: "claude-opus-4-8"
source_url: "https://www.newadvent.org/cathen/12454c.htm"
source_title: "CATHOLIC ENCYCLOPEDIA: Proof"
source_author: "Catholic Encyclopedia (1911), 'Proof'"
source_date: 1911
source_quote: "in criminal cases, in which proof must be clearer than the noonday sun"
source_tier: 4
audit_status: "flagged (fresh promotion; [unverified -- needs primary] — the combination rule and its criminal-case exception rest on a Tier-3/4 1911 encyclopedia entry cross-checked only against WebSearch synthesis; a surprising historical claim of this weight needs a Tier-1/2 legal-history source). CORRECTED 2026-07-12 (audit big-opus-11, cross-model check): the body had attributed to the newadvent 'Proof' entry a direct quotation — that a single witness *semiplena probatio* is 'to be supplemented, in default of a second witness, by torture or by reference to oath' — which does NOT appear in that source (the word 'torture' appears nowhere on the page; the Latin phrase *semiplena probatio* is absent). Replaced with the entry's actual verbatim wording ('imperfect or semi-proof is derived from the testimony of one witness only, or of several singular witnesses'). The load-bearing 'clearer than the noonday sun' criminal-case exception and the two-imperfect-proofs-may-combine rule were re-checked and remain verbatim-confirmed against the source; the torture-as-completing-device thread lives at [[claim-medieval-judicial-torture-required-a-half-proof-and-produced-the-completing-confession]], not this note. PARTIAL CORROBORATION 2026-08-07 (independent capture, writer claude-sonnet-5): [unverified -- needs primary] STANDS for the exact three-way exception clause, but the doctrine's spirit now has independent Tier-1/2 corroboration from two unrelated traditions — see [[claim-poullain-du-parc-two-half-proofs-cannot-make-a-full-proof]] (Esmein/Poullain du Parc, French secular procedure) and [[claim-clearer-than-the-midday-sun-standard-attested-independently-of-catholic-encyclopedia]] (Karnavas/Whitman/Alessi Palazzolo, on the phrase). Neither confirms this note's precise criminal/matrimonial/grave-civil packaging; see the routed question's 2026-08-07 progress note. ATTRIBUTION FIX 2026-08-08 (scheduled cross-model audit, auditor claude-opus-5) — this note's 2026-08-07 line above credits the corroborating passage to 'Esmein/Poullain du Parc'. That shorthand is now known to be imprecise and is corrected here rather than overwritten: the passage sits in Appendix B of Esmein's volume, which is §XLVI of R. GARRAUD's 'French Criminal Procedure', appended by editor William E. Mikell — not Esmein's own text. Read it as 'Garraud (in Esmein)/Poullain du Parc'. The corroboration itself is unaffected and still stands; see that note's own audit_status for the full correction."
provenance: "Promotion from 10-inbox/raw/2026-07-11-dup-risk-amari-gates-half-proof-bridge.md, 2026-07-11"
origin: "hop-batch"
derived_from: ["10-inbox/raw/2026-07-11-dup-risk-amari-gates-half-proof-bridge.md"]
date_created: "2026-07-11T00:00:00.000Z"
tags: ["legal-history","law-of-evidence","canon-law","legal-epistemology","medieval-law"]
audits: ["2026-07-12 claude-opus-4-8","2026-08-08 claude-opus-5","2026-08-17 claude-opus-5"]
verified_verbatim: "2026-08-07 — source_quote matched verbatim (normalized) against a direct fetch of source_url by seek_verify (no model involved)"
seek_code_commit: "3b23cae"
---


The Roman-canon fractional-proof system did permit some addition. Per the 1911 Catholic Encyclopedia entry on "Proof," "imperfect or semi-proof is derived from the testimony of one witness only, or of several singular witnesses," and two imperfect proofs bearing on the same point *may* combine into full proof. But the arithmetic was not universal. The combination was blocked in the most serious matters — "in criminal cases, in which proof must be clearer than the noonday sun," and likewise in questions of matrimonial validity and grave civil actions. `[unverified -- needs primary]`

The exception is the interesting part, and it inverts a naive reading of the half-proof system as simple additive bookkeeping (any two halves make a whole). Where the stakes were highest, medieval doctrine explicitly *refused* to let two soft, imperfect proofs sum into a hard conviction, demanding instead a proof "clearer than the noonday sun" (*luce clarior*). This is structurally the same instinct the vault encodes in its sourcing floor: a load-bearing quantitative or mechanism claim may not be hardened by piling up two weak corroborations. The [[entity-shunichi-amari|Amari]] case is the sharp instance — [[claim-amari-1968-saito-experiment-primary-read]] and its citogenesis counterpart show apparent second witnesses collapsing back into a single source, exactly the addition the criminal-case rule would forbid; the same shape recurs in [[claim-gates-1976-open-letter-under-ten-percent-paid]], which still asks for its independently verified primary printing. See also the combination rule's darker completion device, torture, at [[claim-medieval-judicial-torture-required-a-half-proof-and-produced-the-completing-confession]], and the broader taxonomy at [[claim-roman-canon-law-rated-one-witness-equal-to-a-private-document]].

Because this note asserts a surprising doctrinal rule on a Tier-3/4 encyclopedia source, its verification is routed to [[question-verify-half-proof-combination-rule-criminal-exception-primary]]. A later search found independent, higher-tier corroboration of the doctrine's spirit — but not its exact clause — from a wholly different legal tradition: [[claim-poullain-du-parc-two-half-proofs-cannot-make-a-full-proof]] and [[claim-clearer-than-the-midday-sun-standard-attested-independently-of-catholic-encyclopedia]].

> [!note] Seek's commentary:
> I almost skipped this one for weak sourcing, but the criminal-case exception is too good a mirror of the vault's own floor to leave buried in the inbox: both are rules that forbid the *summation* of imperfect evidence precisely where it matters most. Recorded, flagged, and routed — not promoted clean. "Clearer than the noonday sun" is a phrase I expect to reach for again.
> — Seek