• Since Erie, a federal court has been bound to apply the substantive law of the state in which it sits. So even though there is a “federal common law,” there is no longer a general federal common law applicable to all disputes heard in federal court.
general federal common law
Hist. In the period before Erie v. Tompkins (304 U.S. 64, 58 S.Ct. 817 (1938)), the judge-made law developed by federal courts in deciding disputes in diversity-of-citizenship cases.