Wading Into Erie's Murky Waters in a Shady Grove: Must Federal Courts Apply a State Law Requirement That an Expert Witness Affidavit Accompany a Compliant?

This article considers the Supreme Court appeal in Berk v. Choy, Docket No. 24-440, to be  argued to the Court on October 6, 2025. In this appeal from the Third Circuit, the Court will consider whether a federal court in its diversity jurisdiction must dismiss a case where state law requires the plaintiff to support the complaint with an expert witness affidavit. Since the Court’s Erie decision in 1938, the federal courts have struggled, in case after case, to determine whether state rules, regulations, or policies constitute substantive or procedural law and what tests courts may use to make this determination. The Court has continued to provide evermore layers of  doctrinal analysis, and these cases have rightly earned the label of Erie’s murky waters. The Court’s less than pellucid explication of Erie doctrine in Shady Grove has compounded the complexity of ascertaining applicable law in federal diversity cases. Thus, Berk’s appeal  practically invites the Court to reconsider or to clarify its Shady Grove decision because the parties contend that each has misconstrued and misapplied the Court’s teaching in Shady Grove.