Defences 

Defences are pleaded and proved by the defendant. In negligence they mostly reduce damages; a few defeat the claim. In the intentional torts they are usually the whole contest, because the elements of the tort are easily made out.

Contributory negligence

The plaintiff failed to take reasonable care for their own safety, and that failure contributed to the harm. The standard mirrors the defendant's: what a reasonable person in the plaintiff's position would have done, judged prospectively, with the statutory principles applied in the same way as to a defendant's negligence.

At common law contributory negligence was a complete defence; apportionment legislation in every jurisdiction replaced that with a reduction of damages to the extent the court thinks just and equitable having regard to the plaintiff's share in the responsibility. The apportionment reflects both the relative culpability of each party and the causal potency of their conduct, per Joslyn v Berryman (2003) 214 CLR 552.¹

Most jurisdictions now allow a reduction of 100 per cent where the court considers it just and equitable — restoring, in an extreme case, the effect of the old complete defence. Statutory presumptions of contributory negligence also apply in several jurisdictions where the plaintiff was intoxicated or relied on the skill of a person they knew to be intoxicated.

Voluntary assumption of risk

A complete defence, and a narrow one. The defendant must prove the plaintiff knew of and fully appreciated the specific risk and freely accepted it. Mere knowledge of a general danger, or continuing with an activity, is not enough. Because the standard of proof is demanding, the defence rarely succeeds on its own and has largely been overtaken by the statutory obvious risk provisions.

Obvious risk and dangerous recreational activities

The statutes are the practical route. In broad terms, and with real variation between jurisdictions:

• A plaintiff is presumed to have been aware of an obvious risk unless they prove otherwise, which converts the hardest element of voluntary assumption of risk into a presumption operating in the defendant's favour.
• There is generally no duty to warn of an obvious risk, subject to exceptions.
• A defendant is not liable for harm suffered from the materialisation of an obvious risk of a dangerous recreational activity engaged in by the plaintiff. This is a powerful provision: it operates whether or not the plaintiff was aware of the risk, and it can defeat an otherwise sound claim outright.

What counts as a dangerous recreational activity, and how narrowly the risk is characterised, is where these cases are won and lost, and the answers differ across jurisdictions.

Illegality

There is no general rule that a criminal cannot sue. The principle operates through coherence: a duty is denied, or a defence allowed, where recognising the claim would be inconsistent with the purpose of the criminal law — most clearly where the parties were engaged in a joint criminal enterprise and the injury arose out of it. Several jurisdictions have statutory provisions denying or limiting damages where the harm occurred during the commission of a serious offence.

Defences to the intentional torts

• Consent — the plaintiff consented to the contact or entry. Consent obtained by fraud as to the nature of the act, or exceeded in scope, is no consent. Capacity to consent is its own enquiry, and for medical treatment it is governed by statute in part.
• Self-defence and defence of another — the response must be both necessary and reasonable in the circumstances as the defendant honestly and reasonably perceived them.
• Defence of property — permits reasonable force, and less of it than defence of the person.
• Necessity — an emergency justifying what would otherwise be a trespass, judged objectively and narrowly.
• Lawful authority — the defence that decides most false imprisonment claims, and it is statutory: the arrest, detention and search powers of the jurisdiction, and their conditions.

Limitation periods

An action must be brought within the statutory limitation period, which is not a defence to the merits but ends the claim just as effectively. Periods differ by cause of action and by jurisdiction, personal injury regimes commonly run from the date of discoverability rather than the date of injury, extension powers exist, and several jurisdictions have removed limitation periods altogether for claims arising from child sexual abuse. Check the jurisdiction's Act; nothing here is safely generalised.

Applying this in a problem question

1. Deal with the elements of the tort first. A defence presupposes a completed cause of action.
2. Take the statutory defences before the common law ones — obvious risk and dangerous recreational activity usually decide recreational injury cases.
3. For contributory negligence, identify the specific failure of care, then apportion, giving reasons for the percentage.
4. Keep complete defences separate from reductions in damages, and state which you are arguing.
5. Remember the onus is on the defendant throughout.

Where the authority sits

Apportionment legislation and the civil liability statute of each jurisdiction, read with the common law they modify. The differences between jurisdictions here are larger than anywhere else in tort law, so a defence must be stated for a nominated jurisdiction.