Definition
In pleading, duplicity is the technical fault of combining two or more distinct grounds in a single pleading unit where only one is permitted. The defect appears in three principal contexts:
1. Duplicity in a count or declaration: uniting two or more separate causes of action in a single count of a complaint or writ.
2. Duplicity in a plea: setting up two or more independent grounds of defense in a single plea.
3. Duplicity in a replication or indictment: alleging more than one breach, or in criminal practice, charging more than one distinct offense in a single count.
The underlying principle is that each pleading unit should present a single, discrete legal proposition so that the opposing party can respond clearly and the court can render a definite judgment. Duplicity is a formal defect, not a substantive one — the pleader has stated too much, not stated something wrong.
Common Language
Modern common usage (Wiktionary): Intentional deceptiveness; double-dealing.
Historical common usage (Webster's 1913): Doubleness of heart or speech; insincerity; a sustained form of deception which consists in entertaining or pretending to entertain one set of feelings while acting as if influenced by another; bad faith.
The gap here is almost total. In ordinary English — both modern and historical — duplicity means dishonesty or two-faced deception, carrying a strong moral charge. In law, duplicity is a structural pleading defect with no moral dimension whatsoever. A scrupulously honest pleader can commit duplicity simply by drafting a count that joins two causes of action. Researchers encountering the word in legal sources should not import the common meaning; the legal usage describes a technical fault in form, not a finding of bad faith.
Common Confusion
Duplicity is sometimes confused with multiplicity, but the two defects run in opposite directions. Multiplicity is the fault of bringing multiple counts or charges to address what is in substance a single wrong — too many pleading units for one matter. Duplicity is the fault of stuffing multiple distinct matters into a single pleading unit — too few units for too many matters. A researcher who conflates them will misread arguments about pleading sufficiency in both directions.
Duplicity should also be distinguished from the mere joinder of several facts that together constitute one cause of action or one defense. Bouvier and other sources are explicit: when multiple facts unite to form a single ground of recovery or defense, there is no duplicity. The defect arises only when the pleader joins what are independently sufficient and legally distinct grounds in the same count or plea.
Why It Matters in Research
The practical significance of duplicity has shifted dramatically across legal history, and this shapes how the term appears in corpus sources at different periods.
In common law pleading, duplicity was a live and consequential objection. Because common law pleading required a single issue to emerge from the exchange of pleadings, a duplicate plea prevented the case from narrowing to a triable point. A defendant who pleaded two separate defenses in one plea gave the plaintiff an election — the plaintiff could treat the plea as bad for duplicity and demur, or respond to either ground. The defect was waivable if not timely raised, but it could derail a pleading exchange entirely.
Under code pleading (post-Field Code, 1848 onward) and later under the Federal Rules of Civil Procedure, the rigid single-issue requirement was substantially relaxed. Modern rules expressly permit a party to plead alternative and even inconsistent grounds. As a result, duplicity largely disappeared as a civil pleading objection in modern American practice. Researchers reading nineteenth-century treatises and reports will encounter duplicity arguments constantly; researchers in twentieth-century federal civil practice will encounter them rarely if at all.
Criminal practice is the important exception. Duplicity remains a live doctrine in criminal pleading. A count in an indictment that charges two distinct offenses is duplicitous, and the defect can be grounds for a motion to dismiss or elect. The concern is constitutional as well as formal: a duplicitous count creates ambiguity about what the jury unanimously found, potentially undermining double jeopardy protections. Researchers working on criminal procedure materials should treat duplicity as a living doctrine regardless of the time period.
Jurisdictional traps: Some state courts retained common law pleading requirements long after federal reform, so the term carries full technical weight in older state court records well into the late nineteenth and even early twentieth century depending on the jurisdiction. Scotch law used the related terms duply and duplicatio for a different procedural stage — the defendant's answer to the plaintiff's replication — so researchers in comparative or Scots law materials should not conflate these.
Historical Dictionary Support
The four source dictionaries agree on the core definition but differ in depth and emphasis.
Burrill offers the most economical formulation: "that fault which consists in employing two or more distinct allegations or answers, where one is sufficient," citing Stephen on Pleading. This captures the essential rule cleanly.
Black's adds the three-part structure — count, plea, replication — and notes the Scottish procedural term duply in the same entry, a useful reminder that the Latin root duplicatio produced distinct terms of art in different legal systems.
Bouvier provides the most useful substantive gloss: the union of several facts constituting together but one cause of action does not constitute duplicity. This qualification is essential and is underemphasized by the other dictionaries. Bouvier's entry signals that duplicity analysis requires a judgment about whether multiple allegations are truly independent grounds or merely cumulative facts supporting one ground.
Anderson's Dictionary of Law does not provide a useful entry for this term; the text included in the source material addresses "duly" and related adverbial constructions, not duplicity as a pleading concept.
None of the historical dictionaries address the criminal pleading context with any depth, nor do they discuss how code pleading reform would effectively retire the civil dimension of the doctrine. For that evolution, researchers should consult Stephen's Commentaries on the Laws of England and the notes to the original Field Code.
Jurisdictional Note
Duplicity as a civil pleading defect has been effectively abolished in federal court and in most states that follow the Federal Rules model, where alternative and inconsistent pleading is expressly permitted. In criminal practice, duplicity remains a recognized and litigated defect in both federal and state courts, with constitutional overtones tied to double jeopardy and jury unanimity requirements. Researchers using materials from code-pleading-era state courts should be alert to jurisdictions that retained hybrid or modified pleading rules after 1848.