Definition
In law, "vicious" carries two distinct applications that operate largely independently of each other.
1. Describing animals. An animal is said to have a "vicious propensity" when it has a demonstrated tendency to behave in a way that could endanger persons or property. The standard is broader than mere dangerousness in a single incident: it covers any propensity that creates a risk to others, even if the animal is otherwise useful for the purpose for which it is kept. The concept is central to liability for animal-caused injury, where a keeper's knowledge of the vicious propensity is the operative legal fact.
2. Describing legal instruments, pleadings, or writs. In older legal usage, especially Anglo-Norman and early common-law practice, "vicious" means faulty, defective, or legally insufficient. A vicious writ is one that fails in form or substance. A vicious plea or instrument is one that cannot stand because of some inherent legal defect. This sense is largely archaic in modern practice but appears throughout early English legal materials.
Common Language
Modern common usage (Wiktionary): Violent, destructive, and cruel; savage and aggressive; pertaining to vice or depravity.
Historical common usage (Webster's 1913): Characterized by vice or defects; defective; faulty; addicted to vice; corrupt in principles or conduct; depraved; wicked.
The common meaning has narrowed and intensified over time — today "vicious" typically conjures physical aggression or moral depravity. In legal usage, the term splits in two directions. The animal-law sense aligns loosely with the modern common meaning of aggression, but does not require actual violence — a propensity to bite, kick, or charge suffices even without a prior incident causing harm. The instruments-and-pleadings sense (defective, faulty) has almost no modern common equivalent; this archaic legal meaning survives only in historical sources.
Common Confusion
"Vicious propensity" is sometimes confused with "dangerous propensity" or "ferocious disposition." These terms are often used interchangeably in cases and secondary sources, but "vicious propensity" is the more technical term of art in strict-liability and negligence frameworks for animal-caused injury. Separately, the archaic pleading sense of vicious (defective) can mislead researchers who encounter the term in early English legal materials and read it through the modern behavioral lens.
Why It Matters in Research
Researchers working in animal-liability materials will encounter "vicious propensity" as a threshold legal concept tying keeper liability to prior notice. The critical research question is not whether the animal was vicious in a colloquial sense but whether the keeper had knowledge of the specific propensity at issue — courts have distinguished between propensities that pose general risk and those relevant to the particular injury. The knowledge element and the scope of the propensity have been litigated extensively, and the case law is fact-intensive.
For researchers in early English legal history or Anglo-Norman legal texts, the defect-and-sufficiency sense of vicious is indispensable. Burrill's entries are drawn directly from Britton, one of the early treatises on English common law, where vicious appears repeatedly in the context of writ practice. Readers unfamiliar with this usage will misread passages that describe procedural defects.
The two senses appear in entirely different research contexts and are unlikely to cause confusion within a single document, but researchers building cross-period research trails should flag the divergence early.
Historical Dictionary Support
Anderson's and Burrill's entries reflect the two distinct tracks well, though neither connects them to each other.
Anderson's entry is focused and practical: it defines vicious propensity in the animal-liability context, and usefully emphasizes that the relevant propensity is one endangering safety — not merely one that diminishes the animal's utility. This is a meaningful doctrinal distinction: an animal that has become unreliable or uncooperative is not thereby "vicious" in the legal sense.
Burrill's entry reaches deeper into the historical record, drawing on Britton for the older procedural sense. The Law French examples are genuinely illustrative: "le brefe purra estre vicious en plusurs maneres" (the writ may be faulty in many ways) captures the full flexibility of the term as applied to instruments. Burrill traces the word to "vice" — in the sense of defect — which directly explains the pleading usage.
Neither dictionary addresses how "vicious" functions in moral or criminal characterization (as in "vicious and depraved" as an element of certain offenses), a gap worth noting for researchers in criminal law history where such language appears in older statutes and indictments.
Jurisdictional Note
The "vicious propensity" doctrine originated at common law and persists in many U.S. jurisdictions, but it has been substantially modified or displaced by statute in others. Some states impose strict liability on keepers of animals that cause injury regardless of prior propensity; others retain the knowledge-of-propensity requirement. The applicable framework must be confirmed jurisdiction by jurisdiction.