Definition
A sworn written statement filed by a defendant in a civil action declaring that the defendant has a genuine, meritorious defense to the plaintiff's claim. The affidavit does not argue the defense in full; it attests to the existence of a bona fide ground for contesting the plaintiff's case on the merits. Courts have historically required this document in specific procedural contexts — most commonly to defeat or delay a motion for summary judgment entered without trial, or to forestall judgment by default in jurisdictions that permitted early entry of judgment on certain claims.
The precise content required varied by jurisdiction: some courts demanded that the affidavit identify and describe the specific ground of defense with particularity; others accepted a general sworn declaration that a meritorious defense existed without requiring elaboration.
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Common Confusion
AFFIDAVIT OF DEFENCE vs. AFFIDAVIT OF MERIT: These terms are related but not interchangeable. An affidavit of merit (or certificate of merit) is typically filed by a plaintiff — most often in professional malpractice actions — to attest that the claim has substantive basis before litigation proceeds. An affidavit of defence runs in the opposite direction: it is the defendant's sworn assertion that there is good ground to contest the plaintiff's claim. Researchers encountering older pleading records should not assume the two are synonymous simply because both involve sworn attestations of case merit.
AFFIDAVIT OF DEFENCE vs. PLEA: An affidavit of defence is a procedural instrument, not a substantive pleading. It does not set out the defense in the form required at common law or under code pleading. It is a threshold showing — enough to keep the defendant in court — not the defendant's full legal answer.
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Why It Matters in Research
This term belongs primarily to older American civil procedure, particularly the period running from the mid-nineteenth century through the early twentieth century when courts in several states maintained summary judgment-adjacent procedures requiring defendants to demonstrate that a real defense existed before they could be heard at trial. Researchers working in Pennsylvania practice records will encounter it frequently; Bouvier's citations to Pennsylvania reporters (138 Pa. 974; 187 Pa. 197) reflect that state's well-developed body of doctrine on the subject.
The term largely disappeared from mainstream procedural vocabulary following widespread adoption of the Federal Rules of Civil Procedure in 1938 and analogous state reforms. Modern summary judgment practice under Rule 56 — and its state equivalents — absorbed the function the affidavit of defence once served, though in a substantially restructured form. Researchers reading early twentieth-century treatises or case reporters should understand that references to affidavits of defence describe a pre-Rules procedural landscape that no longer maps cleanly onto contemporary civil practice.
A specific research trap: in jurisdictions that used the affidavit of defence system, failure to file could result in judgment being entered against the defendant without trial, regardless of the underlying merits. The procedural stakes were therefore high, and appellate records from this era often turn on the sufficiency of the affidavit rather than the substance of the defense itself. Do not read those decisions as substantive rulings on the underlying claims.
A secondary use of the phrase appears in real property practice, where sworn affidavits asserting defensive facts — such as adverse possession, prior payment, or absence of encumbrance — were recorded to cure or contest title defects. This usage overlaps conceptually but is analytically distinct from the civil procedure context.
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Historical Dictionary Support
Bouvier's Law Dictionary treats the affidavit of defence as a settled procedural device, defining it as a statement in proper form that the defendant has a good ground of defence on the merits. Bouvier acknowledges the significant jurisdictional variation in required content, noting that some states demanded the affidavit specify the ground of defense while others accepted a simpler general attestation. The citations to Pennsylvania practice (Troubat & Haly's Practice, Pennsylvania reporters) confirm that this was not a uniform national rule but a jurisdiction-by-jurisdiction procedural requirement built up through local court rules and decisional law.
Bouvier's entry, though compressed, captures the essential structure accurately: the affidavit is a gatekeeping device, not a merits instrument. What the historical dictionaries understandably do not address is the degree to which this procedural mechanism was displaced by twentieth-century reform. Researchers relying solely on Bouvier will not find guidance on when and how the affidavit of defence fell out of common use, or how modern summary judgment rules relate to and differ from it.
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Jurisdictional Note
Pennsylvania historically maintained the most elaborated version of affidavit of defence practice, and the Pennsylvania reporters are the richest source of doctrine on the subject. Other states required similar affidavits under local court rules, but requirements as to form and substance varied considerably. Modern American jurisdictions do not generally use this device; analogous protective functions are now served by summary judgment procedure, motions to dismiss, and verified answers.
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Encyclopedia Cross-Reference
The Law Mind Torts & Personal Injury Encyclopedia: "Professional Malpractice — Certificate of Merit / Affidavit of Merit Requirements" (for comparison with the plaintiff-side affidavit of merit device)
The Law Mind Real Estate Transactions & Construction Encyclopedia: "Title Defects and Curative Actions — Quiet Title, Affidavits, and Corrective Instruments" (for the real property recording context in which affidavit-based defensive assertions appear)
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