Definition
In Roman and civil law procedure, the duplicatio is the defendant's formal pleading in response to the plaintiff's replication. It is the fourth pleading in the standard sequence of civil litigation, following the plaintiff's initial claim, the defendant's answer, and the plaintiff's replication. The duplicatio corresponds functionally to the rejoinder in common law pleading practice.
The associated maxim — Duplicationem possibilitatis lex non patitur — means "the law does not allow the doubling of a possibility." This principle operates independently of the pleading term itself and addresses the rule against compounding contingencies in legal obligations.
Common Confusion
DUPLICATIO should not be confused with "duplication" in its ordinary sense of copying or repetition. Despite the surface resemblance, duplicatio is a technical term of art from Roman pleading procedure describing a specific responsive pleading — not any act of doubling or repeating. Researchers encountering the word in civil law or Scots law sources should not interpret it through the lens of its English cognate.
Researchers should also distinguish the pleading duplicatio from the maxim Duplicationem possibilitatis lex non patitur, which historical dictionaries consistently attach to the term. The two are related only by shared Latin root; the maxim does not define or govern the pleading.
Why It Matters in Research
The principal research challenge with duplicatio is jurisdictional and textual displacement. The term belongs to the Roman civil law tradition and surfaces in Anglo-American legal sources primarily through two channels: (1) treatises and commentaries on civil law procedure, including Blackstone's treatment of the pleading sequence, and (2) Scots law, where the term survived in active practice as the "duply" — a near-direct transliteration that Burrill explicitly flags.
Researchers working in Scottish legal history will encounter duply in primary sources where an English common lawyer would expect "rejoinder." Missing this equivalence can cause a researcher to misread the procedural posture of a case. Burrill's reference to Bracton signals that the concept filtered into medieval English legal thought as well, though it did not take hold in English common law pleading nomenclature.
The attached maxim, Duplicationem possibilitatis lex non patitur, appears in Rolle's Abridgment and is occasionally cited in property and contract contexts entirely separate from pleading. A researcher who encounters this maxim in a substantive law discussion should not assume a pleading context — the Latin root has drawn the two concepts together in dictionary entries, but they operate in different doctrinal domains.
Corpus researchers should note that the pleading sequence — libel or declaration, answer, replication, duplicatio, triplicatio — appears consistently in civil law commentaries and will be rendered differently depending on whether the source is translating from Latin, writing in English about civil law, or writing in Scots law. Burrill's note that Halifax translated duplicatio simply as "duplication" illustrates how anglicization can obscure the technical meaning.
Historical Dictionary Support
The four source dictionaries are in close agreement on the core definition. Black's (both editions) and Rapalje & Lawrence give essentially identical short-form entries: the defendant's answer to the plaintiff's replication, corresponding to the common law rejoinder. Burrill provides the most granular treatment and is the most useful entry for research purposes.
Burrill's additions are substantive. He identifies duplicatio as "the fourth pleading in the series," citing Blackstone's Commentaries (3 Bl. Com. 310) — a reference common law researchers will find accessible. He also cites the Institutes (4.14.1) and Heineccius for the civil law grounding, and he alone flags the Scots practice equivalence (duply) and the Halifax translation. These details are absent from the shorter Black's entries.
All four dictionaries append the maxim Duplicationem possibilitatis lex non patitur with the citation to 1 Rolle 321. This uniform attachment suggests the maxim was a standard pedagogical companion to the term, though no dictionary explains the substantive content of the maxim in depth. Researchers seeking the maxim's doctrinal application will need to go beyond dictionary sources.
No source addresses the historical decline of duplicatio as English common law pleading formalized around its own nomenclature, nor do they address how civil procedure reforms in the nineteenth century rendered much of this pleading sequence obsolete in practice.
Jurisdictional Note
Duplicatio is a term of civil law and Roman procedure with no operative role in modern American or English common law practice. It remains relevant primarily in Scots law history, where it survived as "duply," and in scholarship engaging the civil law tradition. Researchers in Louisiana, which retains a civilian heritage, may encounter civil law pleading concepts but modern Louisiana practice uses contemporary Code of Civil Procedure terminology rather than Roman pleading terms.