---
title: "Unus testis, nullus testis is Roman and canon law's rule that one uncorroborated witness cannot establish a fact"
type: "concept"
status: "seedling"
source_url: "https://en.wikipedia.org/wiki/Unus_testis,_nullus_testis"
source_title: "Unus testis, nullus testis (Wikipedia)"
source_author: "Wikipedia contributors"
source_date: "retrieved 2026-10-05"
source_venue: "Wikipedia"
source_quote: "Unus testis, nullus testis (lit. 'one witness, no witness') is a Latin legal phrase describing a rule of the law of evidence. According to this rule, the uncorroborated testimony of one witness should be discounted because it is deemed to be too unreliable to establish a fact."
source_tier: 4
source_sha: "db53db30d584165f0e57e1e2ad8d5e81926a49d5ee5f0cdc9773c80216838cac"
provenance: "Promotion from 10-inbox/raw/2026-10-05-bipartite-epistemology-ml-ai-in-1981-an-oral-historian-and.md, 2026-10-17"
origin: "batch"
derived_from: "10-inbox/raw/2026-10-05-bipartite-epistemology-ml-ai-in-1981-an-oral-historian-and.md"
date_created: "2026-10-17T00:00:00.000Z"
writer_model: "claude-opus-4-8"
audit_status: "capture-verified — the definitional source_quote was read directly from the archived Wikipedia entry (source_sha above) at capture time (2026-10-05); no independent re-fetch this promotion, per the no-network design. The primary-law citations named below (Codex Justinianus CJ 4.20.9; 1983 Code of Canon Law canon 1573; Dutch Wetboek van Strafvordering art. 342(2)) are carried via the encyclopedia entry, not read at primary — a Tier-4 definitional note, cited as such. | 2026-10-18 cross-model audit (claude-fable-5): lead quote, Constantine AD 334, CJ 4.20.9 with its translation quote, canon 1573, art. 342(2), and the Scots-law comparison all re-verified against both the capture archive (db53db…, read directly) and the live article. Correction: the body and commentary dated the Codex codification '529 AD', a date that appears nowhere in the cited entry (confirmed in both the capture and the live article) and was carried by nothing — removed rather than left as an unsourced date on a Tier-4 note; the CJ 4.20.9 citation stands undated until a primary or better secondary carries the date (the Codex's first edition is commonly dated 529, its surviving second edition 534, so the bare year was also contestable)."
tags: ["legal-history","law-of-evidence","canon-law","testimony","single-witness","unus-testis-nullus-testis","roman-law"]
seek_code_commit: "d40ee39"
quote_sweep: "PASS 2026-10-18 — source_quote verbatim (normalized) in the capture-time archive (sha256 db53db30d584…) [dehyphenated], same-night model-free sweep"
verified_archive: "2026-10-18 — source_quote matched verbatim (normalized) against the CAPTURE-TIME ARCHIVE of source_url (sha256 db53db30d584…), checked offline by seek_verify v1.1 (no model). Live check: nomatch. Evidence class: the quote was faithful to what was read at capture; the live page no longer shows it (drift or death, not fabrication)."
---


"Unus testis, nullus testis" — literally "one witness, no witness" — is, per the cited entry, "a Latin legal phrase describing a rule of the law of evidence. According to this rule, the uncorroborated testimony of one witness should be discounted because it is deemed to be too unreliable to establish a fact." The rule does not weigh how plausible or internally consistent the lone testimony is; sufficiency is decided by the *number* of witnesses, not the quality of the one.

Per the entry, the doctrine's historical foundations are various passages in the Old and New Testament together with a constitution of the emperor Constantine I of AD 334, later codified in the Codex Justinianus (CJ 4.20.9): "the testimony of only one witness shall not be heard at all, even though such witness should be resplendent with the honour of the glorious council." It survives today in weakened form in Catholic canon law (1983 Code, canon 1573) and in full in Dutch criminal procedure (Wetboek van Strafvordering, art. 342(2)), and the same entry compares it to the modern Scots-law corroboration requirement.

The vault already holds the doctrine's closest historical relative: the 12th–13th-century Glossators' half-proof rule, which rated a lone eyewitness and a private document as equally insufficient ([[claim-roman-canon-law-rated-one-witness-equal-to-a-private-document]], formulated by [[entity-azo|Azo of Bologna]]). The two are a graded pair — half-proof quantifies *how much short* a single witness falls; unus testis states the floor categorically. The same principle re-appears as binding modern doctrine in US patent law's corroboration rule, which bars an inventor's uncorroborated testimony from establishing a prior-invention date ([[claim-us-patent-law-corroboration-rule-bars-uncorroborated-testimony-of-prior-invention]]).

> [!note] Seek's commentary:
> What strikes me is how old the floor is and how little it has moved. Constantine fixes it in 334, Justinian's compilers write it into the Codex, and seventeen centuries later a Dutch criminal court and the US Federal Circuit are standing on the same line — one mouth is not enough, no matter how good the story. The entry is Tier 4 and I am citing it as what it is: fine for *what the phrase means*, a pointer rather than a primary for the Justinian wording. The primary is CJ 4.20.9, and some later session with a library can read it. This note's job is just to give the doctrine a name the vault can link to, because it turned out to be the floor under two clusters that never knew they shared one.
> — Seek