Definition
Necessity in law refers to a condition of compelling force or unavoidable circumstance that either justifies or excuses conduct that would otherwise be unlawful, or that gives rise to a legal right or obligation by operation of law rather than by agreement or intent.
The term operates across multiple distinct legal contexts:
1. Criminal defense (choice of evils). A defendant acted to prevent a greater harm, and no reasonable lawful alternative was available. The defense requires that the harm avoided outweigh the harm caused, that the threat be imminent, and that the defendant not have created the necessity. Courts divide on whether necessity can excuse intentional homicide.
2. Tort defense — private necessity. A private party who invades another's property or interferes with another's goods to protect their own person or property is privileged to do so but remains liable for actual damages caused. The privilege negates liability for trespass but does not extinguish the duty to compensate.
3. Tort defense — public necessity. A party acting to avert a threat to the public at large (such as destroying property to stop a fire from spreading) is privileged to do so and, in many jurisdictions, bears no liability for resulting harm. The public character of the threat distinguishes this from private necessity.
4. Property law — easement by necessity. When a conveyance leaves a parcel without any access to a public road, courts imply an easement of access over the grantor's remaining land. The easement arises from the necessity created by the severance, not from any express intent of the parties.
5. General common law principle. Necessity carries with it a privilege as to private rights — the Latin maxim necessitas inducit privilegium quoad jura privata, invoked by Bacon and quoted in Burrill, captures the foundational idea that legal obligations yield under sufficiently extreme compulsion.
Common Language
Modern common usage (Wiktionary): The quality or state of being necessary or unavoidable; a pressing need or requisite; something indispensable.
Historical common usage (Webster's 1913): The quality or state of being necessary or absolutely requisite; also, the condition of being needy or necessitous; pressing need or indigence.
The common meanings are descriptive — necessity names a condition of need or unavoidability. The legal meanings are operative: necessity is a doctrine that produces specific consequences. Recognizing that something was "necessary" in the ordinary sense does not automatically trigger any legal doctrine. A researcher must identify which of the distinct legal contexts applies, because the elements, consequences, and available defenses differ substantially across criminal, tort, and property law.
Common Confusion
Necessity and duress are frequently conflated, and historical sources sometimes treat them as interchangeable. They are not. Duress involves compulsion by human threat — a person, typically a third party, coerces the actor through threatened harm. Necessity involves compulsion by circumstances — natural forces, physical conditions, or the logic of events rather than another person's will. The distinction matters procedurally and doctrinally: duress is more often recognized as a complete defense in contract law, while necessity occupies contested ground in criminal law and operates more comfortably as a defense to property-based torts.
Necessity and impossibility are also sometimes conflated in contract contexts, though they are technically distinct doctrines with different triggering conditions.
Core Elements
Criminal necessity defense (majority formulation):
- The defendant faced a specific and imminent threat of harm
- The harm threatened was greater than the harm caused by the unlawful act
- No reasonable lawful alternative was available
- The defendant did not create or substantially contribute to the necessity
- The defendant ceased the unlawful conduct as soon as the necessity ended
Private necessity (tort):
- The defendant intentionally invaded plaintiff's property or goods
- The invasion was reasonably necessary to protect the defendant's person or property from a greater harm
- Defendant remains liable for actual damages (the privilege is incomplete)
Easement by necessity (property):
- Common ownership of dominant and servient parcels at some prior time
- A severance that left one parcel landlocked or without lawful access
- Strict necessity for access at the time of severance (some jurisdictions require reasonable necessity only)
Recognized Forms
/SUBTYPES
Public necessity. The actor invades private rights to protect the public from a common threat. Recognized as a complete privilege in tort; no compensation owed.
Private necessity. The actor invades private rights to protect personal interests. A qualified privilege; damages remain payable.
Necessity as criminal defense (choice of evils). Recognized by statute in many jurisdictions and at common law, though with significant variation on whether homicide can ever be excused.
Easement by necessity. A property law doctrine implying an access right from the circumstances of severance.
Necessity as contract doctrine. Sometimes invoked to excuse non-performance where supervening necessity makes performance impossible or where one party's urgent need is relevant to the formation or enforcement of an agreement, though modern contract law more typically uses the doctrines of impossibility and impracticability.
Why It Matters in Research
The most important navigational point is that necessity is not a single doctrine — it is a word that names several distinct legal constructs that happen to share a common intuition. A case discussing necessity as a criminal defense will be nearly irrelevant to research on easements by necessity, and vice versa. Always identify the branch of law first.
In criminal law sources before the mid-twentieth century, necessity appears less frequently as a formally developed defense and more as a background moral principle. Modern statutory codification (following Model Penal Code § 3.02) gave the criminal necessity defense its current structured form. Researchers using pre-1960 criminal law sources should expect doctrinal treatment to be thinner and to blur into discussions of duress.
In tort law, the public/private distinction carries enormous practical weight: public necessity traditionally confers a complete defense with no compensation obligation, while private necessity requires compensation for actual harm. Early tort treatises do not always draw this line cleanly. Researchers should verify which category applies before relying on older authority.
For property research, easement by necessity is tightly bound to the law of implied easements and to the rule of prior use. These doctrines travel together in most treatises and in the corpus. The necessity must typically exist at the moment of severance — subsequent landlocking generally does not create an easement by necessity unless the jurisdiction allows a relaxed rule.
Admiralty sources introduce yet another specialized meaning. Anderson's entry on necessaries for ships uses "necessity" in the context of maritime supplies and repairs that a vessel requires for its functioning — this is the origin of the admiralty "law of necessaries" and is distinct from all the doctrines above.
Historical Dictionary Support
The historical dictionaries converge on a core formulation: necessity is a controlling, irresistible force that removes or severely constrains voluntary choice. Black's (both editions) leads with "controlling force; irresistible compulsion; a power or impulse so great that it admits no choice of conduct." Bouvier offers the more analytical "that which makes the contrary of a thing impossible." Burrill connects to the Latin maxims — necessitas facit licitum quod alias non est licitum (necessity makes lawful what otherwise is not) — which reveals the classical common law basis for the doctrine's exculpatory function.
All historical sources enumerate the same three traditional categories: preservation of one's own life, obedience to law or superior authority, and necessity arising from act of God or third party. This tripartite structure, drawn from Jacob's Law Dictionary and elaborated by Bouvier, tracks the same intuitions that underlie the modern public/private/criminal taxonomy, though the correspondence is imperfect.
What the historical dictionaries largely miss: the easement by necessity as a fully developed property doctrine, the clean public/private necessity distinction in tort law, and the Model Penal Code's formalization of the criminal choice-of-evils defense. Anderson's is the outlier in the group, pivoting from the general doctrine to admiralty necessaries — a specialized meaning that the other dictionaries do not address and that researchers in maritime law should not overlook.
Jurisdictional Note
Necessity as a criminal defense varies widely: some jurisdictions recognize it by statute (often under the label "choice of evils"), others at common law only, and a small number have rejected it entirely for certain offenses, particularly homicide. Easement by necessity doctrine differs on whether strict necessity or reasonable necessity is required, and on how courts treat the timing of the landlocked condition relative to the original severance.