Where expert evidence establishes that an accident would not have occurred but for any one of several factors, the but for test of causation must be applied to each factor separately; a court cannot apply it to one defendant's negligence and then treat other factors as non-causative merely because the accident would not have occurred but for the first defendant's breach. Apportionment in cases of concurrent fault requires assessment of both causative potency and culpability of each party.
The full text is available to signed-in members, including the 3 later cases that cite this judgment.