A defendant is not liable unless their wrongful conduct in fact causes the claimant’s harm.
The defendant is also not liable merely because their conduct in fact caused the claimant’s harm. There must be both factual and legal causation.
The long accepted test of factual causation is the ‘but-for’ test. One asks whether the claimant’s harm would have occurred in any event without, (that is but-for) the defendant’s conduct. If it would, that conduct is not the cause of the harm. The question is entirely one of fact. The onus is on the claimant to prove the link on the balance of probabilities.
The Constitutional Court in Dudley Lee v Minister of Correctional Services  dealt with the liability of the minister for infection of a prisoner with tuberculosis during his incarceration. The majority judgment held that the lower court had incorrectly applied the common law ‘but-for’ test and that the case didn’t require any development of the common law. The majority said:
“There was thus nothing in our law that prevented the High Court from approaching the question of causation simply by asking whether the factual conditions of Mr Lee’s incarceration were a more probable cause of his tuberculosis, than that which would have been the case had he not been incarcerated in those conditions”.
There has been considerable academic debate as to whether the Lee judgment alters the common law test for factual causation or not.
The Lee test considers whether negligent conduct creates a risk. Even on that test it is important to analyse the risk which was created in order to determine whether that risk can be said to have caused the injury complained about.
The Constitutional Court in Mashongwa v Passenger Rail Agency of South Africa , said:
“Lee never sought to replace the pre-existing approach to factual causation. It adopted an approach to causation premised on the flexibility that has always been recognised in the traditional approach. It is particularly apt where the harm that has ensued is closely connected to an omission of a defendant that carries the duty to prevent the harm. Regard being had to all the facts, the question is whether harm would nevertheless have ensued, even if the omission had not occurred. However, where the traditional ‘but-for’ test is adequate to establish a causal link, it may not be necessary, as in the present case, to resort to the Lee test”.
More recently the Constitutional Court, in BJ de Klerk v Minister of Police, in a judgment primarily dealing with legal causation, again said that the ‘but-for’ test is ordinarily to be applied to determine factual causation, but quoting Lee said that in an appropriate case the test ‘should be relaxed’.
In assisting their insureds to defend claims, insurers should be alert to the fact that the traditional ‘but-for’ test may no longer be appropriate. The question may in a particular case simply be ‘did the risk created by the defendant probably cause the injury or damage?’
That, however, is likely to arise only in exceptional circumstances and not in cases where factual causation is established as a probability on the traditional test.