Definition
Latin: "by itself" or "in itself." In law, per se designates that a thing is treated as legally significant by its own nature, without requiring proof of additional facts, context, or circumstances. The consequence follows from the act or condition alone.
The phrase operates across multiple legal domains, each using the core idea differently:
1. NEGLIGENCE PER SE. A defendant's violation of a statute or regulation constitutes negligence as a matter of law, without requiring the plaintiff to show separately that the conduct fell below a reasonable standard of care. The statutory violation substitutes for the ordinary negligence analysis, provided the plaintiff belongs to the class the statute was meant to protect and suffered the harm the statute was meant to prevent.
2. DEFAMATION PER SE. Certain categories of false statement are so inherently harmful that the plaintiff need not prove actual damages to maintain an action. At common law these categories included imputations of crime, loathsome disease, conduct injurious to trade or profession, and sexual misconduct. Damages are presumed from the statement itself.
3. ANTITRUST PER SE RULES. Under federal antitrust law, certain categories of agreement — principally horizontal price-fixing, market division, and group boycotts — are treated as unlawful per se, meaning no inquiry into competitive effects or market conditions is permitted. The illegality is established by proof of the agreement itself. This contrasts with the rule of reason, which requires a full competitive analysis.
4. PER SE TAKINGS. In constitutional takings doctrine, certain government actions — permanent physical occupation of property, or regulations that eliminate all economic value — are treated as takings per se, requiring just compensation without the balancing analysis applied to regulatory takings generally.
5. GENERAL USE. In briefs, opinions, and legal argument, per se is also used loosely to mean "in and of itself" or "as such," without invoking any formal legal doctrine. Context determines whether a technical doctrine or merely emphatic phrasing is intended.
Common Language
Modern common usage (Wiktionary): "Without determination by or involvement of extraneous factors; by its very nature" or "in a true or literal sense; as one would expect from the name or description."
Historical common usage (Webster's 1913): Not independently defined; used as a Latin phrase meaning "by itself" or "in itself," common in scholarly and philosophical writing.
Editorial note: The common use of per se as emphasis — "that's not illegal per se" — approximates but does not match the legal meaning. In legal doctrine, per se signals a formal rule that forecloses further factual inquiry. When a court says an act is negligent per se or a restraint is unlawful per se, it is not being emphatic; it is specifying that a conclusive legal category applies and that contrary evidence on the general question is inadmissible or irrelevant. Researchers reading historical opinions should not treat per se as mere rhetorical flourish.
Common Confusion
Per se is frequently contrasted with — and confused with — two related standards: rule of reason (in antitrust) and negligence in fact (in tort). The per se/rule of reason divide in antitrust is one of the most litigated structural questions in that field; an agreement labeled per se unlawful receives categorically different treatment than one evaluated under the rule of reason, and courts have shifted some conduct between categories over time. Separately, per se is sometimes conflated with res ipsa loquitur in negligence contexts: both can establish negligence without detailed proof, but they operate differently — per se uses statutory violation as the legal standard; res ipsa uses circumstantial inference of carelessness.
Why It Matters in Research
The phrase appears in a dozen doctrinal contexts, and its meaning is not portable across them. A researcher working on a defamation case who encounters per se in an antitrust opinion, or vice versa, may import the wrong analytical framework entirely.
In historical sources, per se in tort law almost always refers to the defamation or actionable-words context. The negligence per se doctrine, while old, is not always labeled that way in nineteenth-century cases; courts sometimes describe the same principle as the violation of a statute being conclusive evidence of negligence, without using the phrase.
Antitrust per se doctrine is largely a twentieth-century development and will not appear under that label in any historical dictionary. Researchers using Bouvier or Burrill for antitrust work should not expect doctrinal guidance; those sources predate the Sherman Act era analysis entirely.
The constitutional per se takings category is primarily a late-twentieth-century doctrinal development. Historical constitutional materials using per se are unlikely to invoke it as a takings term.
Within the Law Mind corpus, the three encyclopedia entries cross-referenced here cover distinct terrain: the torts encyclopedia entries address negligence per se (statutory violation) and defamation per se (presumed damages) as separate doctrines; the constitutional entry addresses per se rules under the Takings Clause. These should be consulted independently, not interchangeably.
Watch for jurisdictional drift in defamation per se: the categories recognized at common law have been modified or restricted in many states, and First Amendment doctrine has complicated the presumed-damages rule when the plaintiff is a public figure or the matter involves public concern.
Historical Dictionary Support
The historical dictionaries are in full agreement on the Latin meaning and its core legal application. Black's (both editions) defines per se as "by himself or itself; in itself; taken alone; inherently; in isolation; unconnected with other matters" — a purely translational entry that conveys the concept without elaborating on specific doctrines. Burrill adds a citation to a Massachusetts case (3 Pickering's R. 257) in the context of fraud, indicating early American courts applied the phrase in that context. Bouvier gives the most substantive historical entry, anchoring per se specifically in the actionable-words-in-slander context: no special damage need be proved for words actionable per se. Bouvier's cross-references to Libel and Slander confirm that this was the primary doctrinal home of per se in nineteenth-century American law.
What the historical dictionaries miss almost entirely: the antitrust application (post-Sherman Act), the negligence per se doctrine as a labeled category, and the constitutional takings dimension. Researchers relying solely on these sources will find a partial and domain-specific picture. The historical entries are reliable for the defamation/slander lineage but are not a guide to modern per se doctrine in its full scope.
Jurisdictional Note
Defamation per se categories vary by state, and some jurisdictions have narrowed or expanded the common law categories by statute or decision. In antitrust, per se analysis is primarily a federal doctrine under the Sherman Act; state antitrust laws may apply different standards to the same conduct. Negligence per se likewise varies: most states recognize the doctrine but differ on whether statutory violation is conclusive or merely evidence of negligence.
Encyclopedia Cross-Reference
torts_8: Negligence — Negligence Per Se (Violation of Statute as Negligence) (The Law Mind Torts & Personal Injury Encyclopedia)
torts_123: Defamation and Privacy Torts — Defamation Per Se Categories (The Law Mind Torts & Personal Injury Encyclopedia)
constitutional_66: The Takings Clause — Physical Takings and Per Se Rules (The Law Mind Constitutional Law Encyclopedia)