Definition
Latin: "it does not follow." In legal usage, non sequitur identifies a logical defect in argumentation — a conclusion that does not follow necessarily or reasonably from the premises or evidence on which it purports to rest. The term functions less as a discrete legal doctrine and more as a term of logical criticism deployed in briefs, judicial opinions, and legal analysis to expose gaps in reasoning.
In legal argument, a non sequitur may appear in: (1) statutory construction disputes, where a proposed interpretation does not logically flow from the text or legislative history; (2) judicial opinions, where a court identifies that a party's argued conclusion is unsupported by the authority or facts cited; or (3) logical analysis of evidence, where an inference drawn from facts cannot bear the weight assigned to it.
The term carries no procedural force on its own — it is not a motion, a defense, or a cause of action. It is a diagnostic label applied to defective reasoning.
Common Language
Modern common usage (Wiktionary): Any invalid argument in which the conclusion cannot be logically deduced from the premises; also, any abrupt and inexplicable transition or occurrence, or a type of pun built on a listener's violated expectation.
Historical common usage (Webster's 1913): An inference which does not follow from the premises.
The common and legal meanings converge closely here, but with one important gap. In everyday speech, non sequitur has drifted toward describing any jarring or absurd conversational non sequitur — a subject change, a joke, a weird remark. In legal usage, the term retains its strict logical meaning: a conclusion that cannot be derived from stated premises. Legal writers invoking non sequitur are always making a structural argument about the logical integrity of reasoning, not a stylistic observation about awkward transitions.
Common Confusion
Non sequitur is sometimes loosely treated as synonymous with logical fallacy generally. The terms are not interchangeable. A logical fallacy is a broad category encompassing many types of defective reasoning (circular argument, false analogy, ad hominem, etc.). A non sequitur is a specific genus within that category: the defect is the disconnection between premise and conclusion, regardless of whether either the premise or conclusion is itself false. All non sequiturs involve a fallacy, but not all fallacies are non sequiturs.
Why It Matters in Research
Non sequitur appears frequently in appellate opinions as a critical term directed at a party's argument, not as a holding or legal standard. When researching judicial criticism of reasoning, be aware that courts use the phrase without always meaning it in its strict logical sense — sometimes "non sequitur" in an opinion signals that a conclusion is merely unpersuasive, not that a formal logical gap exists. Researchers should read usage in context before relying on a court's invocation of the term as technical logical analysis.
In historical legal sources, the term appears in dictionaries primarily as a transitional vehicle for presenting the maxim Non solent quae abundant vitiare scripturas ("superfluities do not usually vitiate writings") and related Latin maxims. This is a feature of nineteenth-century legal dictionary practice: grouping Latin terms alphabetically caused unrelated maxims to be clustered together under non sequitur as an entry anchor. Researchers encountering non sequitur in a historical legal dictionary should expect the surrounding material to concern surplusage doctrine, not logical argumentation.
The matching encyclopedia entries flagged above — non-solicitation agreements, non-compete clauses, non-disclosure agreements — share only the prefix "non" and are not meaningfully related to this term. That coincidence reflects a search artifact, not a conceptual connection.
Historical Dictionary Support
All four shelf sources — Black's (both editions), Rapalje & Lawrence, and Burrill — define non sequitur identically and briefly: "it does not follow" or "does not follow." None elaborates on the term's application to legal argument. The entries then pivot immediately to unrelated Latin maxims beginning with "non," particularly the surplusage maxim from Digest 50.17.94. Burrill alone cross-references the term to Nonsuit, a procedural device that shares the "non" prefix but is otherwise unrelated — a further illustration of alphabetical grouping rather than conceptual connection.
The uniformity across dictionaries signals that the term was treated as settled, self-defining, and not in need of elaboration. What the historical dictionaries miss entirely is the term's active modern function as a critical tool in legal writing and appellate practice. That application was assumed rather than explained, and researchers relying solely on historical dictionaries will find no practical guidance on how courts and advocates deploy the term.
Jurisdictional Note
Non sequitur as a term of logical criticism operates uniformly across common law jurisdictions. It carries no jurisdiction-specific procedural or substantive content. Variation arises only in how individual courts and legal cultures deploy formal logical vocabulary in opinions and briefs, not in the term's meaning.
Encyclopedia Cross-Reference
No Law Mind Encyclopedia entry directly addresses legal logic, argumentation, or Latin maxims of reasoning. The employment and contracts entries flagged in source matching are not relevant.