Alternative liability is a legal principle that a court may apply in a negligence case when multiple defendants could have caused plaintiff’s injury but the plaintiff cannot prove which one.
Most classes will teach alternative liability as a way to shift the burden of proving causation from the plaintiff to defendants – – each defendant must prove he did NOT cause plaintiff’s injury otherwise defendants are jointly and severally liable to the plaintiff.
Some legal scholars will analyze this on a deeper level and question whether it is really tied to causation.
The case most commonly associated with alternative liability is Summers v Tice. You might see alternative liability applied in modern cases where, say, multiple medical teams treated a plaintiff but there is no way to prove which defendant caused his injury,
Courts have developed sophisticated ways to deal with cases where multiple defendants have caused injuries including liability based on market share.