Procedure, Substance, and Erie

This Article examines the relationship between procedure and substance, and the way in which that relationship affects Erie questions. It first suggests that "procedure" should be understood in terms of process-in other words, in terms of the way that it changes the substance of the law and the value of legal claims. It then argues that the traditional view that the definitions of "procedure" and "substance" change with the context-a pillar on which present Erie analysis is based-is wrong. Finally, it suggests a single process- based principle that reconciles all of the Supreme Court's "procedural Erie" cases: that federal courts can apply their own rules to process a claim as long as, in a costless and outcome-neutral world, those rules do not affect the ex ante value of a claim at the time of its filing.