therefore, a common law right is asserted, we must look to the State in which the controversy originated."[Footnote: Wheaton _v._ Peters, 8 Peters' Reports, 658.] The State courts have looked upon the doctrine announced in Swift _v._ Tyson with an unfriendly eye. In some, its authority is denied.[Footnote: See Porepaugh _v._ Delaware, Lackawanna and Western R. R. Co., 128 Pennsylvania State Reports, 217; 18 Atlantic Reporter, 503.] In none will it affect the disposition of a cause turning upon its own law, and not pending in the federal courts. It has, however, been repeatedly reaffirmed by the Supreme Court of the United States, though the later decisions appear to limit its effect to questions growing out of commercial transactions not wholly confined to a single State.[Footnote: Western Union Telegraph Co. _v._ Call Publishing Co., 181 United States Reports, 92. See Article on the Common Law of the Federal Courts, by Edward C. Eliot, _American Law Review_, XXXVI, 498.] The right of recovery on a cause of action of a commercial nature will therefore often depend on the court which the plaintiff selects. If he sues in a State court, the common law of the State, as the judicial authorities of that State declare it to be, will be applied; if he sues in a court of the United States, the common law of the State as the judicial authorities of the United States declare it to be. Each tribunal will profess to decide by the same rule--the law of the State; but the federal court will really apply the common law of England, as it is generally understood to be, instead of the common law of that State as it is locally understood to be. The relations between the federal and State courts which have been described obviously present many occasions for conflicts of authority. That such conflicts are so infrequent is mainly due to a spirit of comity, which the judges of each sovereignty should and generally do show to those of the other. The federal courts are also prohibited by Act of Congress from issuing any injunction to stay proceedings in a State court, except in certain cases arising under the bankruptcy laws. Independent of any statute, however, the general principles of jurisprudence forbid any direct attempt either by a court of the State to control the action of a court of the United States or by a court of the United States to control the action of a State court, except to the limited extent for which provision is made in the national Constitution.[Footnote: Diggs _v._ Wolcott, 4 Cranch's Reports, 179; M'Kim _v._ Voorhies, 7 Cranch's Reports, 279.] Each court, this exception aside, exercises powers belonging to an independent sovereign, and therefore subject to control by that sovereign only.