Definition
De plain (also rendered de plano) is a Law French phrase meaning "in a summary way" or "on the plain" — that is, proceeding directly, without the formalities or delays of a full hearing. In medieval and early common law usage, a matter decided de plain was resolved on its face, by straightforward consideration, rather than through the elaborate procedural machinery of a solemn trial. The phrase carries the sense of deciding a question summarily, from what is immediately apparent, without extended inquiry.
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Common Language
Modern common usage (Wiktionary): No standard entry. "Plain" in ordinary English means clear, evident, or simple — without ornamentation or obscurity.
Historical common usage (Webster's 1913): "Plain" as an adjective: "Without elevations or depressions; flat; level; — said of a surface. Without ornament; simple; unadorned. Clear; manifest; evident."
The gap here is procedural rather than descriptive. Where ordinary English uses "plain" to describe clarity of meaning, the legal phrase de plain describes a mode of proceeding — summary, direct, without formal pleading or trial. The connection is not incidental: the procedural sense derives from the same root idea of directness and absence of complication, but in legal contexts it carries specific implications about process, not merely about comprehensibility.
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Common Confusion
De plain and de plano are variant forms of the same phrase and are used interchangeably in historical sources. Researchers encountering either form in medieval or early modern legal texts should treat them as equivalent. Neither should be confused with the modern term "plain error" (a standard of appellate review) or the "plain meaning rule" (a canon of contract and statutory interpretation), both of which share the English word "plain" but derive from entirely different conceptual lineages. The historical phrase de plain/de plano concerns procedural informality; modern "plain" usages concern clarity and interpretive method.
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Why It Matters in Research
De plain is an archaic Law French term and will surface almost exclusively in historical sources — medieval legal records, early common law treatises, and glossaries of Law French. Researchers working in those materials need to recognize it as a procedural descriptor, not a term of art with ongoing modern vitality.
The primary research trap is conflation with superficially similar modern terms. A researcher encountering "de plain" in a historical source and a reference to "plain error" in a modern appellate brief is dealing with etymologically related but functionally unrelated concepts. The historical phrase does not anchor or illuminate the modern doctrine; treat them separately.
Burrill's entry cross-references de plano, which is the more commonly encountered Latin form of the same concept and may appear more frequently in ecclesiastical and civil law sources. If your research touches canon law or early equity proceedings, de plano is the form to pursue.
The phrase has no significant jurisdictional variation because it is not operative law in any modern jurisdiction — it appears as a historical descriptor in older records and as a glossary term in law dictionaries of the Burrill era and earlier.
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Historical Dictionary Support
Burrill's Law Dictionary provides the only entry in the Law Mind corpus for this term, defining it concisely: "In a summary way," with attribution to Kelham's glossary of Norman and Old French legal terms and a cross-reference to de plano. This is consistent with the broader historical legal dictionary tradition, in which Law French phrases of this type received brief, functional glosses rather than extended analysis. No disagreement or divergence exists across sources because coverage is effectively limited to Burrill. The sparseness of the entry reflects the term's status: it was already largely antiquarian by the time Burrill compiled his dictionary in the mid-nineteenth century, preserved for completeness rather than practical guidance.
What historical sources do not address is the procedural context in which de plain operated — the specific classes of proceedings, ecclesiastical or common law, in which summary disposition was recognized. Researchers needing that level of detail should look beyond dictionary sources to specialized treatments of medieval procedure and Law French usage.
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Encyclopedia Cross-Reference
Standards of Review on Appeal (De Novo, Abuse of Discretion, Plain Error) — The Law Mind Criminal Law Encyclopedia
Interpretation — Plain Meaning Rule and Four Corners Doctrine — The Law Mind Contracts & Commercial Law Encyclopedia
Note: These entries address modern doctrines that share the word "plain" but are conceptually distinct from de plain as a historical Law French term. They are listed here as orientation points for researchers who encounter the historical phrase while working on research questions that also involve modern plain-error review or plain-meaning interpretation.
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