Hanna (P) was a citizen of Ohio. P filed a tort action in federal court in Massachusetts against Plumer (D), the executor of the estate of Mrs. Osgood, a Massachusetts citizen. Mrs. Osgood caused injuries to P in an auto accident in South Carolina. D was served according to Fed. R. Civ. P. 4(d)(1); by leaving copies of the summons with D's wife at his residence. D made a motion for summary judgment; the service should have been affected pursuant to Massachusetts law under the Erie doctrine. Massachusetts law requires that service to an executor be handed to the party personally within one year. The trial court granted D's motion. P appealed; Erie should not affect the application of the Federal Rules of Civil Procedure to this case. D argued that a substantive law question under Erie is any question which would alter the outcome of the case if federal law were applied to it as long as this application would fit the outcome determinative test. D reasoned that Erie requires application of the state law with respect to service. The District Court granted D’s motion for summary judgment; the state statute was outcome determinative and under York service was improper. The court of appeals affirmed the lower court decision because the conflict between the rules was substantive rather than procedural. Certiorari was granted.