"In determining what did happen in the past a court decides on the balance of probabilities. Anything that is more probable than not it treats as certain." Diplock LJ, Mallet v McMonagle.
- "But For" Test
The basic test is to ask whether the injury would have occurred before, or without, the accused party's breach of the duty owed to the injured party. Even more precisely, if a breaching party materially increases the risk of harm to another, then the breaching party can be sued to the value of harm that he caused.
Notwithstanding the fact that causation may be established in the above situations, the law often intervenes and says that it will nevertheless not hold the defendant liable because in the circumstances the defendant is not to be understood, in a legal sense, as having caused the loss
The most important doctrine is that of novus actus interveniens, which means a ‘new intervening act’ which may ‘cut the chain of causation’.
Breaking the Chain
Whether the acts of a third party break the chain of causation depends on whether the intervention was foreseeable. The general rule is that the original defendant will be held responsible for harm caused by a third party as a direct result of his or her negligence, provided it was a highly likely consequence.
where the defendant has control over the third party, or where the third party is faced with a dilemma created by the defendant, the chain of causation is unlikely to be broken and the defendant will normally be liable to the claimant for the damage caused