Definition
A bill of proof is a procedural device used in English practice — specifically in proceedings before the Mayor's Court of London — by which a third party who claims ownership of property asserts that claim in order to be heard in a dispute to which they are not an original party. When goods or property are the subject of litigation between two parties, a bill of proof allows the true owner, standing outside the suit, to step in and establish their title before the court resolves the matter against their interest.
The device arose in the context of foreign attachment proceedings. Under that procedure, a garnishee — a party holding property belonging to an absent defendant — could not defeat the attachment by arguing that the defendant lacked good title to the property, even if the garnishee knew the property actually belonged to someone else. The garnishee's defenses were limited. The actual owner, however, was not similarly constrained. That owner could file a bill of proof to assert their claim directly, essentially intervening to prove that the attached property was theirs and therefore not properly subject to the attachment at all.
In this sense, the bill of proof functions as a formal third-party claim or intervention mechanism, tailored to the specific procedural rules of the Mayor's Court of London.
Common Confusion
The word "proof" in this term does not carry its ordinary evidentiary meaning — it is not a document proving a fact in the way a receipt or certificate might. The bill of proof is not a bill of evidence. It is a claim, a formal pleading by a third party asserting ownership. The confusion is compounded because "bill" in historical English legal practice had a broad procedural meaning covering instruments now better described as petitions, claims, or pleadings. A researcher encountering this term in archival sources should treat it as a pleading mechanism, not an evidentiary submission.
Why It Matters in Research
This term is narrow in application — geographically confined to the Mayor's Court of London and procedurally confined to foreign attachment — but it matters for researchers working with English commercial litigation records, particularly those involving trade disputes, merchant creditors, and absent debtors in the eighteenth and nineteenth centuries. The Mayor's Court of London handled a significant volume of commercial disputes during that period, and foreign attachment was a frequently invoked remedy in that court.
The key research trap is this: because the garnishee could not raise the third party's title as a defense, disputes over ownership could appear resolved in the main record even when a third party had a legitimate competing claim. The bill of proof created a separate track for that claim. Researchers who look only at the main litigation record may miss entirely that a third-party ownership dispute existed and was separately adjudicated. Look for supplemental filings and court minutes when reviewing Mayor's Court records involving attachment.
The term does not appear to have migrated into American practice in any established form. Researchers working with American sources will not encounter it in domestic proceedings. Its relevance to American legal research is therefore primarily historical and comparative — understanding the English procedural background from which early American commercial law developed.
Historical Dictionary Support
The three source dictionaries agree on all substantive points. Bouvier is the most concise, identifying the bill of proof as a third-party claim to subject matter in dispute before the Mayor's Court and citing Chitty's Practice and Marshall. Rapalje and Lawrence provide the most procedurally precise account, explaining why the device was necessary — the garnishee's disability to raise the defendant's want of title as a defense — and describing the bill of proof as the mechanism by which the true owner fills that procedural gap. Black's entry, though partially truncated in the available text, confirms the same definition: a third-party intervention by someone claiming the subject matter of an existing suit.
None of the three source dictionaries address any American equivalent or successor procedure. None flag whether the device survived consolidation of English civil procedure in the nineteenth century following the Judicature Acts. The Rapalje and Lawrence entry is the most useful for understanding the functional logic of the device, and researchers should begin there before turning to the procedural treatises cited in Bouvier.
Jurisdictional Note
The bill of proof is an English procedural device specific to the Mayor's Court of London. It has no recognized American counterpart. Modern researchers seeking analogous third-party claim mechanisms in American practice should look to intervention under civil procedure rules rather than any direct descendant of this device.