Core legal doctrines, explained

The neighbour principle holds that you owe a legal duty to take reasonable care to avoid acts or omissions you can reasonably foresee would be likely to injure your “neighbour” — anyone so closely and directly affected by your act that you ought reasonably to have them in contemplation.

Under Caparo Industries v Dickman, a duty of care arises where three conditions are met: (1) the harm was reasonably foreseeable, (2) there was a relationship of proximity between the parties, and (3) it is fair, just and reasonable to impose a duty.

Vicarious liability makes one party (usually an employer) liable for the torts of another (usually an employee) committed in the course of employment, even though the employer is not personally at fault.

In negligence a defendant is only liable for damage of a kind that was reasonably foreseeable; harm that is too remote — an unforeseeable type of damage — is not recoverable even if it was factually caused.

Occupiers' liability is the duty an occupier of premises owes to people on their land: a “common duty of care” to lawful visitors under the Occupiers' Liability Act 1957, and a narrower duty to trespassers under the Occupiers' Liability Act 1984.

The standard of care in negligence is that of the reasonable person doing the activity in question; for professionals it is the Bolam standard — a professional is not negligent if they acted in accordance with a practice accepted as proper by a responsible body of opinion in their field.

Causation in negligence has two parts: factual causation (the “but-for” test — would the harm have occurred but for the defendant's breach?) and legal causation (whether the chain is broken by an intervening act, a novus actus interveniens).

Negligent misstatement is liability in tort for a careless statement that causes another pure economic loss, where the maker assumed responsibility towards the claimant and the claimant reasonably relied on the statement — established in Hedley Byrne v Heller.

Private nuisance is an unlawful, substantial and unreasonable interference with a person's use or enjoyment of their land, or of some right over it. Because it protects interests in land, the claimant must usually have a proprietary interest.

Trespass to the person comprises three intentional torts: assault (causing apprehension of immediate unlawful force), battery (the actual infliction of unlawful force), and false imprisonment (the complete restriction of someone's freedom of movement without lawful justification).

Defamation is the publication of a statement that lowers the claimant in the estimation of right-thinking members of society. Under the Defamation Act 2013 the statement must also have caused, or be likely to cause, serious harm to reputation.

Consideration is the price each party pays for the other's promise — something of value (a benefit to one party or a detriment to the other) given in exchange. A promise is only enforceable as a contract if it is supported by consideration, or made by deed.

Promissory estoppel can stop a party going back on a promise — even one unsupported by consideration — where they intended it to be relied upon, the other party did rely on it, and it would be inequitable to let them resile.

A contract is frustrated — and automatically discharged — where, after it is formed, an unforeseen event for which neither party is at fault makes performance impossible, illegal, or radically different from what was agreed.

A misrepresentation is a false statement of fact made by one party that induces the other to enter the contract; it can be fraudulent, negligent or innocent, and may entitle the misled party to rescission and/or damages.

A contract requires agreement: a definite offer by one party that is accepted unconditionally by the other. An offer must be distinguished from an invitation to treat, and acceptance must generally be communicated to the offeror.

An exclusion (or exemption) clause tries to exclude or limit a party's liability. To be effective it must be incorporated into the contract, must on its true construction cover the loss, and must survive statutory controls — chiefly the Unfair Contract Terms Act 1977 and the Consumer Rights Act 2015.

Contract terms are classified by importance: conditions (major terms whose breach lets the innocent party terminate and claim damages), warranties (minor terms giving damages only), and innominate terms (judged by the seriousness of the actual breach).

The primary remedy for breach of contract is damages, aimed at putting the innocent party in the position they would have been in had the contract been performed (the expectation measure); equitable remedies such as specific performance are available only where damages are inadequate.

Duress and undue influence are vitiating factors that make a contract voidable: duress is illegitimate pressure (to the person, to goods, or economic) that leaves the victim no practical choice; undue influence is the improper use of a relationship of trust or ascendancy to procure agreement.

Unjust enrichment is the principle that a person who has been enriched at another's expense, in circumstances the law treats as unjust, must make restitution. The framework asks four questions: was the defendant enriched, at the claimant's expense, unjustly, and are there defences?

The ratio decidendi is the legal principle or reasoning that was necessary to the court's decision — it is the binding part of a judgment under the doctrine of precedent. Obiter dicta are remarks “said by the way” that were not essential to the outcome, and are only persuasive.

The doctrine of precedent (stare decisis) requires courts to follow the legal principles (ratio decidendi) laid down in earlier decisions of higher courts — and often their own — to ensure the law is consistent and predictable.

Mens rea is the “guilty mind” — the mental element of a criminal offence. Its main forms are intention, recklessness and (for some offences) negligence, and it must normally coincide in time with the actus reus.

Actus reus is the “guilty act” — the physical element of a crime: the prohibited conduct, any required circumstances, and (for result crimes) the consequences. It can include an omission where the defendant was under a legal duty to act.

Theft is defined by s 1 of the Theft Act 1968 as dishonestly appropriating property belonging to another with the intention of permanently depriving the other of it. All five elements must be proved.

The classic grounds on which courts review the lawfulness of a public body's decision are illegality, irrationality and procedural impropriety, as set out by Lord Diplock in the GCHQ case — with proportionality increasingly recognised as a further ground.

Parliamentary sovereignty is the principle that Parliament is the supreme legal authority: it can make or unmake any law, and no court or other body can override or set aside an Act of Parliament.

The separation of powers is the principle that the state's three functions — the legislature (makes law), the executive (implements it) and the judiciary (interprets it) — should be exercised by separate bodies to prevent any dangerous concentration of power.

The rule of law is the principle that everyone — including the government — is subject to and accountable under the law, which must be applied equally, be prospective and clear, and operate through fair procedures rather than arbitrary power.

The doctrine of ultra vires means a public body acts unlawfully if it goes beyond the powers granted to it by law. It is the constitutional foundation of judicial review, ensuring public bodies act only within their legal authority.

An easement is a right enjoyed by one piece of land (the dominant tenement) over neighbouring land (the servient tenement) — such as a right of way or a right to light. The classic requirements were set out in Re Ellenborough Park.