Causation in negligence
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).
Last reviewed 14 June 2026
Factual causation uses the but-for test (Barnett v Chelsea & Kensington Hospital Management Committee [1969] 1 QB 428). Where several causes operate, “material contribution” (Bonnington Castings v Wardlaw) or, in limited cases, “material increase in risk” (Fairchild) may apply.
Legal causation asks whether a later event breaks the chain: a free, deliberate and informed act of a third party or the claimant, or an unforeseeable natural event, may be a novus actus interveniens that relieves the defendant of liability for the later harm.
Key cases
- Barnett v Chelsea & Kensington Hospital Management Committee [1969] 1 QB 428
- Bonnington Castings Ltd v Wardlaw [1956] AC 613
- Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22
Frequently asked questions
What is the but-for test in negligence?
The test for factual causation: would the claimant's harm have occurred but for the defendant's breach? If not, factual causation is established (Barnett v Chelsea).
What is a novus actus interveniens?
A new intervening act — by a third party, the claimant, or nature — that breaks the chain of legal causation and ends the defendant's liability for the later harm.