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Legal theories
Legal structure

The doctrines that decide cases.

Every claim runs on a legal theory — a chain of elements the two sides fight over. Here they are in plain English: what each requires, when it applies, and how it is proven or broken.

Tort

Duty of Care

The threshold legal obligation to act as a reasonably prudent person would, owed to those foreseeably put at risk by one's conduct.

Tort

But-For Causation

The threshold factual test asking whether the injury would have occurred absent the defendant's conduct -- distinct from the legal, policy-driven question of proximate cause.

Tort

Contributory Negligence

The traditional common-law rule that any negligence by the plaintiff, however slight, completely bars recovery -- now the minority rule, largely superseded by comparative negligence.

Tort

Attractive Nuisance Doctrine

A premises-liability exception holding a landowner liable for injuries to trespassing children caused by hazardous conditions likely to attract them, even absent an invitation.

Civil Procedure

Res Judicata

The doctrine barring relitigation of a claim that was, or could have been, raised in a prior action that ended in a final judgment on the merits between the same parties.

Contract

Novation

A three-way agreement that substitutes a new party or a new obligation for an existing contract, completely extinguishing the original obligation rather than merely transferring it.

Contract

Accord and Satisfaction

An agreement to discharge an existing, disputed obligation by accepting a different performance than originally owed, and the actual performance of that agreement.

Contract & Tort

Mitigation of Damages

The rule that an injured party must take reasonable steps to minimize losses after a breach or injury, and cannot recover damages that reasonable mitigation would have avoided.

Contract

Statute of Frauds

The rule requiring certain categories of contracts to be evidenced by a signed writing to be enforceable, designed to prevent fraudulent claims about the existence of an oral agreement.

Contract

Parol Evidence Rule

The rule that bars extrinsic evidence of prior or contemporaneous agreements to contradict or vary the terms of a final, integrated written contract.

Contract

Apparent Authority

The doctrine binding a principal to an agent's act because the principal's own conduct reasonably led a third party to believe the agent had authority to act, whether or not actual authority existed.

Contract

Constructive Trust

An equitable remedy that treats a defendant as holding specific property as trustee for the rightful owner, used to prevent unjust enrichment when property was acquired through wrongdoing or mistake.

Contract

Equitable Estoppel

The doctrine barring a party from asserting a right or fact where its own conduct or representations induced another party's reasonable, detrimental reliance to the contrary.

Contract

Implied Covenant of Good Faith and Fair Dealing

The default contract term, read into virtually every agreement, that neither party will act to destroy or injure the other's right to receive the benefits of the contract.

Contract

At-Will Employment Exceptions

The recognized exceptions -- public-policy, implied-contract, and covenant-based -- that narrow the default rule allowing an employer to terminate employment for any reason or no reason at all.

Tort

Negligent Misrepresentation

A tort claim for pecuniary loss caused by a false statement of material fact that the defendant made carelessly, without the intent to deceive required for fraud.

Corporate

Successor Liability

The doctrine determining when a company that acquires another company's assets also inherits its predecessor's liabilities, despite the general rule that an asset buyer takes assets free of the seller's debts.

Tort

Failure to Warn

A products-liability theory holding a manufacturer or seller liable for injuries caused by a product's foreseeable danger that was not adequately disclosed to the user, even when the product itself was properly designed and made.

Contract

Economic Duress

A doctrine that voids an agreement made under an improper economic threat that left the victim no reasonable alternative but to consent.

Equity

Unclean Hands

An equitable defense that bars a plaintiff from obtaining equitable relief when the plaintiff's own misconduct is directly connected to the claim.

Contract

Breach of Implied Warranty

A claim that goods or services failed to meet quality or fitness standards the law imposes automatically, without any express promise to that effect.

Tort

Negligent Entrustment

A tort claim against a person who supplies a dangerous instrumentality, like a vehicle, to someone they know or should know is likely to use it unsafely.

Tort

Private Nuisance

A tort claim for a substantial and unreasonable interference with another person's use and enjoyment of their own land.

Tort

Conversion

A tort claim for the wrongful exercise of dominion or control over another's personal property that seriously interferes with the owner's rights.

Tort

Malicious Prosecution

A tort claim for initiating or continuing a prior legal proceeding without probable cause and for an improper purpose, after that proceeding ended favorably to the plaintiff.

Tort

Abuse of Process

A tort claim for using legitimately issued legal process for a collateral, improper purpose it was not designed to serve.

Tort

Respondeat Superior

The doctrine that holds an employer liable for torts an employee commits within the scope of employment.

Tort

Res Ipsa Loquitur

An evidentiary rule that lets negligence be inferred from an accident that ordinarily would not happen without negligence.

Corporate

Piercing the Corporate Veil

The equitable remedy that lets a court hold shareholders personally liable for a corporation's obligations.

Tort

Proximate Cause

The requirement that a defendant's conduct be a legally close enough cause of the harm to justify liability.

Contract

Promissory Estoppel

A doctrine that enforces a promise, even without a bargained-for exchange, when the promisee reasonably relied on it to their detriment.

Contract

Unjust Enrichment

An equitable claim requiring a party who has been unfairly benefited at another's expense to make restitution.

Tort

Negligence Per Se

A doctrine treating violation of a safety statute as itself the breach element of negligence when the plaintiff is in the class the law protects.

Tort

Assumption of Risk

A defense that bars or reduces recovery when a plaintiff knowingly and voluntarily accepted a known danger.

Tort

Comparative Negligence

A system that reduces a plaintiff's recovery in proportion to the plaintiff's own share of fault for the harm.

Procedure

Doctrine of Laches

An equitable defense barring a claim when a plaintiff's unreasonable delay in suing has prejudiced the defendant.

Contract

Quantum Meruit

A claim to recover the reasonable value of services or goods provided when no enforceable contract fixes the price.

Tort

Tortious Interference

A tort claim against a third party who wrongfully disrupts another's contract or prospective business relationship.

Tort

Strict Liability

Liability imposed without proof of fault, chiefly for defective products and abnormally dangerous activities.

Corporate

Breach of Fiduciary Duty

A claim that someone who owed a heightened duty of loyalty or care violated it and harmed the person who trusted them.

Tort

Negligent Infliction of Emotional Distress (NIED)

A claim for emotional harm caused by another's carelessness, with elements that vary sharply by state.

Tort

Intentional Infliction of Emotional Distress (IIED)

A claim for severe emotional harm caused by conduct so outrageous it exceeds all bounds tolerated in a civilized society.

Tort

Fraudulent Concealment

Fraud committed by actively hiding a material fact a party had a duty to disclose, rather than by an affirmative lie.

Tort

Civil Conspiracy

A theory holding two or more people jointly liable for agreeing to and furthering an underlying wrong -- not a standalone tort.

Evidence

Spoliation of Evidence

The destruction, alteration, or loss of evidence relevant to litigation, which can trigger sanctions or an adverse inference.

Tort

Joint and Several Liability

A liability rule letting a plaintiff collect a full judgment from any one defendant, regardless of that defendant's share of fault.

Corporate

Alter Ego Doctrine

A doctrine holding an owner or parent liable by treating them and a controlled entity as legally the same when unity of interest exists.

Contract

Economic Loss Rule

A rule generally barring tort recovery for purely economic losses arising from a contract, absent injury or damage to other property.

Procedure

Collateral Estoppel (Issue Preclusion)

Issue preclusion doctrine barring relitigation of an issue actually litigated and necessarily decided in an earlier case.

Tort

Eggshell Skull Rule

A tort principle making a defendant liable for the full extent of an injury, even when a pre-existing condition makes it unusually severe.

Insurance

Duty to Defend vs. Duty to Indemnify

The distinction between a liability insurer's broad obligation to defend an insured against a lawsuit and its narrower obligation to actually pay a judgment or settlement.

Insurance

Occurrence vs. Claims-Made Trigger

The two dominant methods liability policies use to decide which policy period applies to a loss: when the injury happened, or when the claim was reported.

Tort

Market Share Liability

A limited, minority tort doctrine that lets a plaintiff recover from multiple manufacturers of a fungible, defective product in proportion to their share of the relevant market when the plaintiff cannot identify which specific manufacturer's product caused the injury.

Tort

Enterprise Liability

A rarely-adopted tort theory holding an entire group of manufacturers in an industry jointly liable for an injury caused by a defective product when the specific manufacturer cannot be identified and the group jointly controlled the relevant risk, such as through shared industry-wide safety standards.

Tort

Apparent Agency

A doctrine holding a principal liable for the acts of someone who is not actually its employee or agent, when the principal's own conduct led a third party to reasonably and justifiably believe an agency relationship existed and the third party relied on that belief.

Tort

Negligent Supervision

A doctrine holding an employer, school, or other institution directly liable for its own failure to adequately monitor, oversee, or control a person under its authority, where that failure allowed the person to cause foreseeable harm to a third party.

Tort

Negligent Training

A doctrine holding an employer directly liable for injuries to a third party that were proximately caused by the employer's failure to provide adequate training reasonably necessary for an employee to safely perform a role that carries a foreseeable risk of harm.

Tort

Premises Liability: Invitee, Licensee, and Trespasser

The traditional common-law framework classifying visitors to land into three categories — invitee, licensee, and trespasser — each owed a different duty of care by the person or entity in possession of the property.

Tort

Open and Obvious Danger Doctrine

A doctrine limiting or eliminating a landowner's duty to warn of, or in some jurisdictions to remedy, a danger so apparent that a visitor exercising reasonable care should be expected to discover and appreciate it without a warning.

Tort

Primary vs. Secondary Assumption of Risk

The distinction between risks so inherent to an activity that they negate the defendant's duty altogether (primary assumption of risk) and a plaintiff's voluntary encounter with a risk created by the defendant's own negligence (secondary assumption of risk), which merely factors into comparative fault rather than barring the claim.

Tort / Statutory Liability

Dram Shop Liability

Liability imposed on bars, restaurants, and other commercial alcohol sellers for harm an intoxicated patron causes to a third party after being served.

Tort / Medical Malpractice

Loss of Chance Doctrine

A doctrine, mainly in medical malpractice, that lets a patient recover for a defendant's negligent destruction of a chance at a better outcome, even when that chance was already under 50%.

Tort / Medical Malpractice

Informed Consent Doctrine

The physician's duty to disclose material risks, benefits, and alternatives of a proposed treatment so the patient can make a genuinely informed decision.

Procedural / Equitable

Judicial Estoppel

Bars a party from taking a position in litigation that clearly contradicts a position it successfully persuaded a court to accept in an earlier proceeding.

Procedural

Law of the Case Doctrine

Once a court decides an issue at one stage of a case, that ruling governs later stages of the same litigation, including on remand or appeal.

Property

Adverse Possession

A doctrine that lets a person who occupies another's land openly, continuously, and without permission for a statutory period acquire legal title to it.

Property / Landlord-Tenant

Constructive Eviction

A doctrine that relieves a tenant of the duty to pay rent when a landlord's acts or failures render the premises unfit, forcing the tenant to abandon it.

Property / Landlord-Tenant

Implied Warranty of Habitability

An implied promise in residential leases that the premises meet basic standards of safety and livability throughout the tenancy, regardless of the lease's terms.

Contract

Unconscionability Doctrine

A contract defense letting a court refuse to enforce a contract or clause so one-sided or unfairly procured that enforcing it would shock the conscience.

Contract

Anticipatory Repudiation

A doctrine allowing a party to treat a contract as breached, and to sue immediately, when the other side clearly indicates before performance is due that it will not perform.

Contract

Specific Performance

An equitable remedy ordering a breaching party to actually perform its contractual promise, available only when money damages cannot adequately fix the harm.

Contract

Rescission of Contract

An equitable remedy that unwinds a contract entirely, restoring both parties to the position they occupied before the agreement, rather than enforcing or compensating for it.

Contract

Reformation of Contract

An equitable remedy in which a court rewrites the written text of a contract to match the parties' actual agreement, then enforces the corrected version.

Contract

Impossibility and Impracticability of Performance

Doctrines excusing contract performance when an unforeseen supervening event makes performance objectively impossible, or, more flexibly, commercially impracticable.

Contract

Frustration of Purpose

A doctrine excusing performance when a supervening event destroys the principal purpose both parties understood the contract to serve, even though performance itself remains possible.

Contract

Condition Precedent vs. Condition Subsequent

The distinction between an event that must occur before a contractual duty arises (condition precedent) and one that, if it occurs, extinguishes a duty that already existed (condition subsequent).

Contract

Third-Party Beneficiary Rights

The doctrine determining when a person who is not a party to a contract can nonetheless enforce it, distinguishing an intended beneficiary with enforceable rights from a mere incidental beneficiary with none.

Contract

Assignment and Delegation of Contract Rights

The distinction between transferring a contract right to receive performance (assignment) and transferring a contract duty to render performance (delegation), and the different rules governing each.

Contract

Perfect Tender Rule

The UCC rule letting a buyer reject a single-delivery shipment of goods that fails to conform to the contract in any respect, without the common-law materiality threshold.

Contract

Risk of Loss in Sale of Goods

The UCC framework deciding which party bears the loss when goods are damaged or destroyed after contracting but before risk has shifted, independent of who holds title.

Contract

Cover (UCC Buyer's Remedy)

The UCC remedy letting a buyer, after a seller's breach, purchase substitute goods in good faith and without unreasonable delay, then recover the difference between the cover price and the contract price.

Contract

Course of Dealing and Usage of Trade

UCC interpretive tools that fill gaps and clarify ambiguous contract terms using the parties' own prior conduct and the established practices of their trade.

Contract

Battle of the Forms

The UCC 2-207 framework for deciding which terms govern when a buyer's and seller's standardized forms don't match, replacing the common-law mirror-image rule.

Contract

Integration Clause / Merger Clause

A contract provision declaring the written agreement the complete and final expression of the parties' deal, intended to bar reliance on prior or contemporaneous statements not included in the writing.

Contract

Waiver vs. Estoppel in Contract Performance

Two distinct doctrines excusing strict contract performance: waiver is the intentional, voluntary relinquishment of a known contract right, while estoppel bars enforcement of a right because the other party reasonably and detrimentally relied on conduct suggesting it would not be enforced.

Contract

Time Is of the Essence Clause

A contract provision making strict, punctual performance a material term, so that even a minor delay can constitute a breach excusing the other party's performance.

Civil Rights

Qualified Immunity

A doctrine shielding individual government officials from personal-capacity liability for constitutional violations unless the right they violated was 'clearly established' at the time of the conduct.

Civil Rights

Bivens Claims

A judicially implied damages remedy allowing an individual to sue a federal official personally for certain constitutional violations, in the absence of any authorizing statute.

Constitutional

State Action Doctrine

The threshold doctrine holding that most constitutional protections restrain government conduct, not private conduct, so a plaintiff must first show the challenged conduct is fairly attributable to the state before a constitutional claim can proceed.

Civil Rights

Monell Municipal Liability

The doctrine governing when a local government entity itself -- rather than an individual official -- can be held liable under Section 1983 for a constitutional violation, limited to harms caused by the entity's own policy or custom.

Civil Rights

Deliberate Indifference Standard

A demanding state-of-mind standard, sitting between ordinary negligence and purposeful intent, requiring proof that an official or entity was subjectively aware of a substantial risk of harm and consciously disregarded it.

Constitutional

Procedural Due Process

The doctrine requiring that before government deprives a person of life, liberty, or property, it must provide fair procedures -- generally notice and a meaningful opportunity to be heard.

Constitutional

Substantive Due Process

The doctrine holding that certain government actions are unconstitutional regardless of the fairness of the procedures used -- either because they infringe a fundamental right, or because they are so arbitrary that they shock the conscience.

Constitutional

Rational Basis vs. Strict Scrutiny Review

The tiered framework courts use to evaluate constitutional challenges to government action, ranging from highly deferential rational-basis review to the exacting strict-scrutiny standard, with intermediate scrutiny occupying the middle tier.

Insurance

Bad-Faith Failure to Settle Within Limits

The liability doctrine an insured or excess carrier invokes when a primary insurer rejects a reasonable within-limits settlement demand and a judgment later exceeds the policy limits.

Insurance

Excess Verdict and Insurer Exposure

How a judgment exceeding the policy's limits shifts financial exposure between the insured and the insurer, and what determines who ultimately bears the excess amount.

Insurance

Duty to Cooperate Insurance Clause

The policy condition requiring an insured to assist the insurer's investigation and defense, and the circumstances under which a breach can forfeit coverage.

Insurance

Notice-Prejudice Rule

The rule determining whether an insured's late notice of a claim defeats coverage, and whether the insurer must show actual harm from the delay to enforce a notice condition.

Insurance

Exhaustion of Primary Coverage

The general requirement that an underlying primary (or lower-layer) policy pay out its full limits before an excess or umbrella policy's coverage obligation is triggered.

Insurance

Horizontal vs. Vertical Exhaustion

The two competing rules for how an insured must exhaust multiple applicable insurance policies -- across policy years or across coverage layers -- before a given excess policy must pay.

Insurance

Additional Insured Endorsement Scope

The doctrine governing how far a policy endorsement extending coverage to a party beyond the original named insured actually reaches, and what limits its scope.

Insurance

Reservation of Rights Letter

The written notice an insurer sends when it agrees to defend a claim while preserving its right to later contest coverage, and what that letter must accomplish to be effective.

Property

Res Nullius and Abandonment of Property

The doctrine governing ownerless property: things never owned (res nullius) and things an owner intentionally gave up (abandonment) both become available to whoever first takes possession.

Property

Accession and the Fixtures Doctrine

The property-law rules that decide who owns something once one owner's material has been added to, mixed with, or annexed to property belonging to another.

Tort

Tortious Interference with Inheritance Expectancy

A tort claim, distinct from a will contest, for intentionally and wrongfully interfering with an expected gift or inheritance -- available only where the wrongdoing goes beyond simply changing the testator's mind.

Tort

Negligent Spoliation Doctrine

The unsettled question of whether negligent, unintentional destruction of evidence can support its own tort claim for damages -- distinct from spoliation sanctions available inside the underlying case.

Tort

Sudden Emergency Doctrine

A doctrine that judges a defendant's conduct during a sudden, unforeseen emergency by what a reasonable person would do under those same emergency conditions -- an adjusted standard of care, not a defense that excuses liability outright.

Tort

Last Clear Chance Doctrine

A doctrine that lets a plaintiff's claim survive contributory negligence's harsh, complete bar when the defendant had a final, real opportunity to avoid the harm and failed to take it.

Defamation

Mere Conduit Defense

A defamation defense for parties who only passively transmit or distribute content authored by someone else, without editorial control over or knowledge of its defamatory character.

Defamation

Innocent Construction Rule

A threshold defamatory-meaning rule under which, if a statement is reasonably capable of a non-defamatory interpretation, some jurisdictions require courts to adopt that innocent reading and dismiss the claim rather than let a jury choose among competing meanings.

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