Multiple Causation, Apportionment, and the Shapley Value

Multiple causation is one of the most intricate issues in contemporary tort law. Apportioning a loss suffered by a victim among multiple tortfeasors is indeed difficult, and courts do not always follow clear and consistent principles. Here, we argue that the axiomatic approach provided by the theory of cooperative games can be used to clarify that issue. We previously considered the question from a purely game-theoretic point of view. Here we analyze it from a legal perspective. We consider in particular the difficult case of successive causation to which we associate a general class of games called sequential liability games. We show that our model rationalizes the two-step process proposed by Restatement (Third) of Torts, apportionment by causation and apportionment by responsibility. More precisely, we show that the weighted Shapley value is the legal counterpart of this two-step process.