Appellate court
The Appellate court concluded that the federal district court must act as if it were a state court of the state in question, so long as the application of the state's substantive law might change the outcome of the case. This led to the anomaly that the federal courts must treat certain things (such as burdens of proof and statutes of limitations) as substantive law, even if the state treats these same things as merely procedural, as a justification for using their own law instead of the law of another state.