To demonstrate causation in tort law, the claimant must establish that the loss they have suffered was caused by the defendant. In most cases a simple application of the 'but for' test will resolve the question of causation in tort law. Ie 'but for' the defendant's actions, would the claimant have suffered the loss? If yes, the defendant is not liable. If no, the defendant is liable. Causation may be problematic where there exists more than one possible cause. Various formulations have evolved to ease the burden of proving causation in such situations.
The 'But for' test
For application of the 'but for' test in establishing causation in tort law see:
Barnett v Chelsea & Kensington Hospital [1969] 1 QB 428 Case summary
Where there exist two causes occurring in succession it may be possible to identify the factual cause of the damage. However at times policy factors may come into play:
Where there exist two or more causes which operate concurrently it may be factually impossible to determine which one was the cause. This has proved problematic not least because it is the claimant's responsibility to establish which one was the cause. On general principles the burden of proving this is on the balance of probabilities ie the claimant has to demonstrate that there is more than a 50% likelihood of the cause being the breach of duty of the defendant. Where there are two causes this means the burden of proof is impossible to discharge leaving the claimant uncompensated often for an obvious breach of duty. Various formulations have arisen to circumvent the strict approach.
Where there is a new intervening act this may break thechain of causation removing liability from the defendant. The legal test applicable will depend upon whether the new act was that of a third party or an act of the claimant.
Novus actus interveniens - Act of 3rd party
Where the new act is of a third party, the test is whether the act was foreseeable. If the act of the third party was foreseeable, the defendant remains liable and the chain of causation remains in tact. If the act of a third party is not foreseeable this will break the chain of causation and the defendant is not liable for the actions of the third party:
Where the new intervening act is that of the claimant, the test is whether the claimant acted reasonably in the circumstances. If the claimant's actions are deemed reasonable the chain of causation remains in tact and the defendant is liable for the actions of the claimant. If, however, the claimant's actions are unreasonable in the circumstances the chain of causation is broken and the defendant is not liable for the actions of the claimant:
Where the claimant submits the defendant's conduct lost them a chance of avoiding harm or injury as opposed to causing the harm or injury itself, the courts have been reluctant at imposing liability. This most commonly comes up in relation to medical negligence whereby a failure to diagnose a condition correctly may prevent the claimant from receiving vital treatment which may have saved their life or avoided a deteriation in their condition. The House of Lords has twice considered this issue of causation and on each occasion has refused to impose liability:
