518 U.S. 604, 626, 116 S.Ct. 2309, 2321, 135 L.Ed.2d 795 (1996) (explaining that “the ‘principles that animate our policy of stare decisis caution against overruling a longstanding precedent on a theory not argued by the parties’ ” (quoting United States v. Int’l Bus. Machs. Corp., 517 U.S. 843, 855, 856, 116 S.Ct. 1793, 1800, 1801, 135 L.Ed.2d 124 (1996))). As in Pennsylvania, the decisions in which the High Court has taken the extraordinary step of reordering rules of decision on its own motion tend to be ones of widespread application that have generated ongoing controversy. Indeed, the majority’s categorization of its Freed decision with such watershed decisions of civil and criminal procedure as Erie Railroad Company v. Tompkins, 304 U.S. 64, 58 S.Ct. 817, 82 L.Ed. 1188 (1938) (<HOLDING>), and Mapp v. Ohio, 367 U.S. 643, 81 S.Ct.
holding that in a diversity action a federal court must apply the law of the forum state holding that federal courts sitting in diversity shall apply state substantive law holding that state substantive rules of decision apply in federal diversity cases holding that a federal court in diversity jurisdiction must apply state substantive law holding that in diversity cases federal courts are to apply state substantive law and federal procedural law