Definition
The right to use reasonable force to protect oneself, another person, or property against an imminent threat of harm. As a legal concept, self defence operates primarily as a justification or excuse in criminal law, negating criminal liability when a person uses force — including lethal force — in response to an unlawful attack.
Self defence encompasses three related but distinct contexts:
1. Defence of person: The use of force to protect oneself from imminent bodily harm or death.
2. Defence of others: The use of force to protect a third party facing the same threat.
3. Defence of property: The use of force to prevent unlawful interference with property, subject to stricter limitations than personal defence.
The term appears in both British and American legal traditions. In American usage, the spelling "self-defense" is standard; "self defence" remains the British and Commonwealth form. The legal doctrine is substantively the same under either spelling, though rules governing its application vary considerably between jurisdictions and legal systems.
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Common Language
Modern common usage (Wiktionary): Alternative spelling of self-defense.
Historical common usage (Webster's 1913): The act of defending one's own person, property, or reputation.
The common usage tracks the legal meaning closely in broad strokes, but misses the doctrinal structure that makes self defence legally operative. In law, self defence is not merely a description of protective action — it is a structured legal defence with formal elements (imminence, proportionality, necessity, and in some jurisdictions, a duty to retreat) that must be established to avoid criminal liability. The ordinary speaker who "acted in self-defence" may not have satisfied any of these requirements.
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Common Confusion
Self defence is often conflated with two adjacent doctrines. First, the Castle Doctrine, which modifies self defence by eliminating or limiting the duty to retreat when a person is attacked in their home. The Castle Doctrine is a rule about where and when one may stand firm — it does not independently justify force but shapes the retreat requirement within self defence analysis. Second, Stand Your Ground rules, which extend Castle Doctrine logic to any location where a person has a lawful right to be. Researchers should not treat these doctrines as synonymous: self defence is the parent concept; Castle Doctrine and Stand Your Ground are jurisdictional modifications to one of its elements.
Self defence as justification should also be distinguished from self defence as excuse. A justification says the conduct was lawful. An excuse concedes the conduct was wrong but holds the actor not blameworthy. Modern American and English law tends to frame self defence as a justification, but historical sources are inconsistent, and some framing — particularly around excessive force — shades toward excuse.
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Core Elements
The traditional elements of a valid self defence claim, as recognized across most common law systems:
1. Imminence: The threatened harm must be immediate or about to occur. A response to a past harm or a speculative future threat generally does not qualify.
2. Necessity: Force must have been necessary to prevent the harm — no reasonable non-forceful alternative was available.
3. Proportionality: The degree of force used must not exceed what was reasonably necessary to meet the threat. Lethal force is ordinarily justified only in response to a threat of death or serious bodily harm.
4. Honest and reasonable belief: The actor must have genuinely believed force was necessary, and that belief must have been reasonable under the circumstances.
5. Duty to retreat (where applicable): In some jurisdictions, a person must attempt to retreat before using deadly force, unless the Castle Doctrine or Stand Your Ground rule applies.
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Recognized Forms
/SUBTYPES
- Defence of person (self defence proper)
- Defence of others (third-party defence)
- Defence of property
- Castle Doctrine (modified duty-to-retreat rule in the home)
- Stand Your Ground (abrogation of duty to retreat in public spaces)
- Imperfect self defence (honest but unreasonable belief in necessity — reduces liability without fully excusing it in some jurisdictions)
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Why It Matters in Research
Spelling is a research trap. Legal databases, historical sources, and Commonwealth authorities use "self defence" while American sources use "self-defense." A search using only one form will miss a substantial body of material, particularly in English and Canadian sources. Treat both spellings as required search terms.
The doctrine has evolved significantly. Nineteenth-century authorities — including those cited in Burrill — were written against a backdrop of duty-to-retreat rules inherited from English common law. Contemporary American doctrine in many states has moved sharply in the opposite direction through Stand Your Ground legislation. Research into the historical development of self defence must account for this reversal: sources from the same jurisdiction may describe nearly opposite rules depending on their date.
Burrill's reference to Wharton's American Criminal Law points researchers toward an authoritative nineteenth-century treatise synthesis, but Wharton's reflects the pre-Stand Your Ground landscape entirely. Do not apply Wharton's framing to modern statutory schemes without checking intervening legislative change.
The three-way split between defence of person, defence of others, and defence of property is legally important, not merely taxonomic. Defence of property carries the most restrictions — lethal force to defend property alone is almost universally disfavored in modern law — and collapsing these categories in research leads to doctrinal error.
Imperfect self defence, where recognized, creates a distinct sentencing and liability category that does not appear in older authorities and requires targeted research in modern case law.
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Historical Dictionary Support
Burrill defines self defence concisely as "the protection of one's person or property against some injury attempted by another" and identifies it as "an excuse for the use of force in resisting an attack on the person, and especially for killing an assailant." The definition is accurate as a summary of the nineteenth-century common law position.
Two features of Burrill's treatment are worth noting. First, the grouping of person and property under a single definition reflects the older doctrinal framing in which both were protected interests of roughly comparable standing — a framing that modern law has largely abandoned in favor of sharply tiered rules. Second, Burrill characterizes self defence as an "excuse," which carries technical significance: later and current doctrine in most American jurisdictions re-classifies it as a justification. The distinction matters when researching acquittal versus other disposition outcomes, and when analyzing whether an accomplice or third party benefits from the principal's self defence claim.
Burrill's entry is competent but thin by modern standards. It provides no treatment of imminence, proportionality, or the duty-to-retreat debate — all of which were live doctrinal issues in his era and are central to modern self defence analysis.
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Jurisdictional Note
American jurisdictions divide sharply on the duty to retreat, with a substantial number having enacted Stand Your Ground statutes that eliminate the requirement in public spaces. English law imposes no duty to retreat per se but requires that force be "reasonable in the circumstances," a standard that incorporates the possibility of retreat as a factor. Commonwealth jurisdictions (Canada, Australia) follow their own statutory and common law frameworks that diverge from both American and English rules in material respects.
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Encyclopedia Cross-Reference
Self-Defense — Castle Doctrine (The Law Mind Criminal Law Encyclopedia)
Self-Defense — Defense of Others (The Law Mind Criminal Law Encyclopedia)
Self-Defense — Defense of Property (The Law Mind Criminal Law Encyclopedia)
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