Affirmative Defences in the Federal Rules of Civil Procedure Explained

An affirmative defence in the Federal Rules of Civil Procedure Rule 8(c) is a defence raised by a defendant that introduces new facts or legal arguments which defeat or limit the plaintiff’s claim, even if the allegations in the complaint are assumed to be true. Instead of simply denying the plaintiff’s allegations, the defendant accepts that the facts might be true but argues that there is an additional legal reason why the defendant should not be liable.

Under Rule 8(c), a defendant must affirmatively state these defences in the answer to the complaint. If the defendant fails to plead an affirmative defence in the answer, the defence may be waived, meaning the defendant might lose the right to rely on it later in the litigation. The rule lists several common affirmative defences such as statute of limitations, res judicata, waiver, and payment, but the list is not exhaustive, and courts may recognize other affirmative defences depending on the circumstances.

The purpose of requiring affirmative defences to be pleaded early is fair notice. If the defence in the answer is clearly stated, the defendant informs the plaintiff and the court about the legal issues that will be raised in the case. This allows the plaintiff to prepare a response and ensures that the dispute can be resolved efficiently.

For example, if a plaintiff sues for breach of contract, the defendant might raise the statute of limitations as an affirmative defence. The defendant does not deny that a contract existed or that it may have been breached. Instead, the defendant argues that the claim was filed too late under the applicable limitation period, which legally bars the lawsuit even if the plaintiff’s allegations are true.

In total, 18 affirmative defences are listed under Rule 8(c). Each is explained as follows:

Accord and Satisfaction
Accord and satisfaction arises where the parties agree to resolve a dispute by substituting a new performance for the original obligation and that substituted performance is completed. The accord is the agreement to accept different performance, and the satisfaction is the execution of that agreement. Once the satisfaction occurs, the original claim is discharged and the plaintiff cannot sue on the original obligation. For example, a contractor claims a client owes $10,000 for work performed. The client disputes the amount and both parties agree that payment of $7,000 will settle the dispute. Once the $7,000 is paid and accepted, the contractor cannot later sue for the remaining $3,000.

Arbitration and Award
This defence applies where the dispute has already been submitted to arbitration pursuant to an agreement between the parties and the arbitrator has issued a binding award. Because the matter has already been resolved through the agreed dispute-resolution mechanism, the plaintiff is barred from relitigating the same claim in court. For example, two companies have a contract requiring disputes to be resolved by arbitration. They arbitrate a payment dispute and the arbitrator rules in favor of the defendant. If the plaintiff later files a lawsuit on the same dispute, the defendant can plead arbitration and award.

Assumption of Risk
Assumption of risk arises where the plaintiff knowingly and voluntarily exposed themselves to a known danger created by the defendant. If the plaintiff understood the risk and chose to proceed anyway, the defendant may avoid liability because the plaintiff effectively consented to the risk of injury. For example, a spectator attends a baseball game and is hit by a foul ball. Because spectators are generally aware of this risk when attending a game, the stadium owner may raise assumption of risk as a defence.

Contributory Negligence
Contributory negligence is a defence asserting that the plaintiff’s own negligence contributed to the harm suffered. In jurisdictions applying pure contributory negligence, any fault by the plaintiff may completely bar recovery; in comparative fault jurisdictions, the plaintiff’s damages are reduced in proportion to their share of responsibility. For example, a pedestrian crosses a road while texting and is struck by a car that was slightly speeding. The driver may argue that the pedestrian’s own negligence contributed to the accident.

Duress
Duress is raised when a party claims that a contract or agreement underlying the plaintiff’s claim was entered into because of unlawful threats, coercion, or improper pressure. If the defendant can show the obligation arose from such compulsion, the agreement may be void or voidable and cannot be enforced. For example, a business owner signs a contract transferring property after being threatened with physical harm if they refuse. The owner can later argue that the agreement was made under duress.

Estoppel
Estoppel prevents a party from asserting a claim or legal position that contradicts their previous representations or conduct when another party reasonably relied on that conduct to their detriment. The defence is designed to promote fairness by preventing parties from acting inconsistently in a way that harms others. For example, a landlord tells a tenant that rent will not be required for two months during repairs. The tenant relies on that statement and spends the money elsewhere. The landlord may be estopped from later demanding the unpaid rent for those months.

Failure of Consideration
Failure of consideration occurs when the promised exchange underlying a contract fails or is never delivered. Even if a contract was initially valid, if the consideration promised by the plaintiff was not provided or later failed, the defendant may assert that there is no enforceable obligation remaining. For example, a buyer agrees to pay $5,000 for a piece of equipment that the seller promises to deliver. If the seller never delivers the equipment, the buyer may raise failure of consideration when sued for payment.

Fraud
Fraud as an affirmative defence alleges that the plaintiff’s claim is based on fraudulent conduct, such as intentional misrepresentation of material facts made to induce reliance. If the defendant shows that the agreement or transaction was procured by fraud, the resulting obligation may be voidable and unenforceable. For example, a seller falsely claims that a car has never been in an accident. The buyer later discovers serious accident damage and refuses to complete payment, raising fraud as a defence.

Illegality
The defence of illegality arises when the claim is based on a contract or transaction that violates statutory law or public policy. Courts generally refuse to enforce illegal agreements, meaning that a plaintiff cannot recover damages based on a contract that was unlawful from the outset. For example, two parties enter a contract to sell prohibited drugs. If one party sues to enforce payment under the agreement, the defendant can raise illegality as a defence.

Injury by Fellow Servant
This is a historically recognised defence in employment law where an employer argued that a worker’s injury was caused by the negligence of another employee rather than the employer. Under the traditional “fellow servant rule,” the employer was not liable for injuries caused solely by the negligence of a co-worker. For example, a factory worker is injured because a coworker negligently operates machinery. The employer argues that the injury was caused by a fellow employee rather than by the employer’s negligence.

Laches
Laches is an equitable defence that bars claims where the plaintiff has unreasonably delayed bringing suit and that delay has prejudiced the defendant. Even if a claim is technically within the statutory time limit, an excessive and unjustified delay that harms the defendant’s ability to defend the case may prevent relief. For example, a property owner waits many years before suing a neighbour over a fence built on disputed land, during which time the neighbour has invested money improving the property.

License
License is a defence asserting that the defendant had permission or legal authority to engage in the conduct alleged to be wrongful. If the plaintiff consented to the defendant’s actions, such as permitting entry onto land, the conduct is not considered unlawful. For example, a homeowner invites a neighbour onto their land to cut down a tree. The homeowner later sues for trespass, but the neighbour can argue that they had a license to enter the property.

Payment
The defence of payment asserts that the defendant has already fulfilled the obligation underlying the plaintiff’s claim. If the defendant can show that the debt or obligation has been fully paid or satisfied, there is no remaining liability. For example, a lender sues a borrower claiming a loan has not been repaid. The borrower produces records showing the loan was fully paid last year.

Release
A release occurs when the plaintiff has voluntarily agreed to relinquish their legal claim, usually through a written agreement. If a valid release exists, the plaintiff is barred from pursuing the claim because they previously agreed to discharge the defendant from liability. For example, after a car accident, the injured driver signs a settlement agreement releasing the other driver from liability in exchange for payment. The injured driver later attempts to file a lawsuit, but the defendant raises the release.

Res Judicata
Res judicata, also known as claim preclusion, bars a party from relitigating a claim that has already been finally adjudicated by a competent court. If the same parties previously litigated the same claim and received a final judgment on the merits, the matter cannot be brought again. For example, a plaintiff sues a contractor for breach of contract and loses at trial. The plaintiff later files another lawsuit based on the same contract dispute. The contractor can raise res judicata.

Statute of Frauds
The statute of frauds requires certain types of contracts, such as those involving interests in land or agreements that cannot be performed within one year, to be in writing and signed by the party to be charged. If the plaintiff seeks to enforce an agreement that falls within the statute but lacks the required writing, the defendant may raise this defence. For example, a person claims there was an oral agreement to sell land, but there is no written contract. The defendant may raise the statute of frauds.

Statute of Limitations
The statute of limitations bars claims that are brought after the legally prescribed time period for filing a lawsuit has expired. If the plaintiff files suit after the applicable limitation period has run, the defendant can assert this defence to prevent the claim from proceeding. For example, a person injured in an accident waits five years to file a negligence claim even though the relevant limitation period is two years.

Waiver
Waiver occurs when a party intentionally and voluntarily relinquishes a known legal right. If the plaintiff previously waived the right they now seek to enforce, through words, conduct, or agreement, the defendant may rely on that waiver to defeat the claim. For example, a landlord repeatedly accepts late rent payments without objection. When the landlord later tries to evict the tenant solely because of late payments, the tenant may argue that the landlord waived the right to strict enforcement of the payment deadline.