Definition
An argument ab inconvenienti is a form of legal reasoning that urges rejection of a proposed interpretation of law on the ground that accepting it would produce inconvenient, absurd, or practically unworkable results. The argument does not attack the proposed construction on its textual merits or logical structure directly; instead, it points to the downstream consequences of adopting that construction and contends those consequences are so problematic that the interpretation must be wrong. Courts and advocates invoke it as a check on literal or overly narrow readings that would technically satisfy the words of a statute or rule but would create results the law could not plausibly have intended.
The argument operates as a form of reductio: if interpretation X leads to consequence Y, and Y is manifestly inconvenient or absurd, then X should be rejected in favor of a reading that avoids Y. It belongs to the broader family of purposivist and consequentialist interpretive moves, sitting alongside arguments from absurdity and arguments from legislative intent.
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Common Confusion
The argument ab inconvenienti is closely related to, but distinct from, the absurdity canon. The absurdity canon is a rule of statutory construction that permits departure from plain text when a literal reading produces absurd results — a formal doctrine with recognized doctrinal status in most jurisdictions. The argument ab inconvenienti is a broader and older form of advocacy: it encompasses practical inconvenience short of outright absurdity, and it need not operate as a named canon at all. A court may invoke the absurdity canon; an advocate deploys the argument ab inconvenienti. Researchers should not assume the two terms are interchangeable, particularly in older sources where ab inconvenienti appears as a stand-alone category of argument rather than as a synonym for the modern canon.
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Why It Matters in Research
The phrase is almost entirely a creature of older legal literature and classical legal reasoning. Researchers will encounter it primarily in pre-twentieth-century treatises, English common law sources, and American cases decided before statutory interpretation became a formalized doctrinal field. It rarely appears by name in modern American judicial opinions, though the underlying reasoning — "this construction would produce inconvenient or unworkable results" — remains ubiquitous in modern legal argument under different labels.
Two navigational traps are worth flagging. First, because the phrase is Latin and appears most visibly in older dictionaries, researchers may underestimate its continued functional relevance. Courts today frequently accept or reject arguments on ab inconvenienti grounds without naming them as such, framing the same logic as purposivism, the absurdity canon, or pragmatic construction. Tracing the intellectual lineage of a modern court's consequentialist reasoning may require connecting it to this older vocabulary. Second, the argument has variable weight depending on interpretive framework. In textualist analysis, consequences are generally a weak basis for departing from plain meaning; in purposivist or common-law reasoning, they carry more force. Researchers working across historical periods should be alert to this shift in the argument's persuasive authority.
The argument also appears in the context of equity and common law pleading, where it was sometimes invoked to resist the application of rigid procedural rules that would defeat a just result. Its scope in older sources is therefore somewhat broader than a purely statutory-interpretation framing would suggest.
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Historical Dictionary Support
Both editions of Black's Law Dictionary provide identical, minimal definitions: "An argument arising from the inconvenience which the proposed construction of the law would create." The consistency across editions is unremarkable here because the phrase had no doctrinal development to track — it remained a stable label for a classical form of argument rather than a term with an evolving legal meaning.
What the dictionary entries do not capture is the argument's pedigree and its weight as a recognized move in classical legal reasoning. In the common law tradition, ab inconvenienti reasoning was treated as a legitimate but secondary form of argument — useful for resolving ambiguity or confirming a preferred construction, but generally insufficient on its own to override clear text. The argument functions best when paired with other interpretive supports. Black's entries, taken alone, give the researcher the definition but none of this doctrinal texture.
Neither edition of Black's situates the argument within the broader taxonomy of legal argument forms or connects it explicitly to the absurdity canon, purposivism, or equitable construction. Researchers should supplement with treatise sources on statutory interpretation and classical common law reasoning to get the full picture.
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Jurisdictional Note
The argument appears across common law jurisdictions without significant variation in its basic character, though its persuasive weight varies with the interpretive methodology a given court favors. Courts in the English tradition have historically given it more explicit recognition than modern American federal courts, where textualist methodology has reduced reliance on consequentialist reasoning as an independent interpretive ground.
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