64 Opinion of BUTLER, J. courts to exert the judicial power of the United States, and especially § 34 of that Act as construed, is unconstitutional; that federal courts are now bound to follow decisions of the courts of the State in which the controversies arise; and that Congress is powerless otherwise to ordain. It is hard to foresee the consequences of the radical change so made. Our opinion in the Taxicab case cites numerous decisions of this Court which serve in part to indicate the field from which it is now intended forever to bar the federal courts. It extends to all matters of contracts and torts not positively governed by state enactments. Counsel searching for precedent and reasoning to disclose common-law principles on which to guide clients and conduct litigation are by this decision told that as to all of these questions the decisions of this Court and other federal courts are no longer anywhere authoritative. This Court has often emphasized its reluctance to consider constitutional questions, and that legislation will not be held invalid as repugnant to the fundamental law if the case may be decided upon any other ground. In view of grave consequences liable to result from erroneous exertion of its power to set aside legislation, the Court should move cautiously, seek assistance of counsel, act only after ample deliberation, show that the question is before the Court, that its decision cannot be avoided by construction of the statute assailed or otherwise, indicate precisely the principle or provision of the Constitution held to have been transgressed, and fully disclose the reasons and authorities found to warrant the conclusion of invalidity. These safeguards against the improvident use of the great power to invalidate legislation are so well-grounded and familiar that statement of reasons or citation of authority to support them is no longer necessary. But see e. g.: Charles River Bridge v. Warren Bridge, 11 Pet. 420, 553; Township of Pine Grove v. Talcott, 19 Wall. 666, 673; Chicago & G. T. Ry. Co. v. Wellman, 143 U. S. 339, 345; Opinion of BUTLER, J. 304 U.S. Baker v. Grice, 169 U. S. 284, 292; Martin v. District of Columbia, 205 U. S. 135, 140. So far as appears, no litigant has ever challenged the power of Congress to establish the rule as construed. It has so long endured that its destruction now without appropriate deliberation cannot be justified. There is nothing in the opinion to suggest that consideration of any constitutional question is neccssary to a decision of the case. By way of reasoning, it contains nothing that requires the conclusion reached. Admittedly, there is no authority to support that conclusion. Against the protest of those joining in this opinion, the Court declines to assign the case for .reargument. It may not justly be assumed that the labor and argument of counsel for the parties would not disclose the right conclusion and aid the Court in the statement of reasons to support it. Indeed, it would have been appropriate to give Congress opportunity to be heard before devesting it of power to prescribe rules of decision to be followed in the courts of the United States. See Myers v. United States, 272 U. S. 52, 176. The course pursued by the Court in this case is repugnant to the Act of Congress of August 24, 1937, 50 Stat. 751. It declares: "That whenever the constitutionality of any Act of Congress affecting the public interest is drawn in question in any court of the United States in any suit or proceeding to which the United States, or any agency thereof, or any officer or employee thereof, as such officer or employee, is not a party, the court having jurisdiction of the suit or proceeding shall certify such fact to the Attorney General. In any such case the court shall permit the United States to intervene and become a party for presentation of evidence (if evidence is otherwise. receivable in such suit or proceeding) and argument upon the question of the constitutionality of such Act. In any such suit or proceeding the United States shall, subject to the applicable provisions of law, have all the rights of a 64 Opinion of BUTLER, J. party and the liabilities of a party as to court costs to the extent necessary for a proper presentation of the facts and law relating to the constitutionality of such Act." That provision extends to this Court. § 5. If defendant had applied for and obtained the writ of certiorari upon the claim that, as now held, Congress has no power to prescribe the rule of decision, § 34 as construed, it would have been the duty of this Court to issue the prescribed certificate to the Attorney General in order that the United States might intervene and be heard on the constitutional question. Within the purpose of the statute and its true intent and meaning, the constitutionality of that measure has been "drawn in question." Congress intended to give the United States the right to be heard in every case involving constitutionality of an Act affecting the public interest. In view of the rule that, in the absence of challenge of constitutionality, statutes will not here be invalidated on that ground, the Act of August 24, 1937 extends to cases where constitutionality is first "drawn in question" by the Court. No extraordinary or unusual action by the Court after submission of the cause should be permitted to frustrate the wholesome purpose of that Act. The duty it imposes ought here to be willingly assumed. If it were doubtful whether this case is within the scope of the Act, the Court should give the United States opportunity to intervene and, if so advised, to present argument on the constitutional question, for undoubtedly it is one of great public importance. That would be to construe the Act according to its meaning. The Court's opinion in its first sentence defines the question to be whether the doctrine of Swift v. Tyson shall now be disapproved; it recites (p. 72) that Congress is without power to prescribe rules of decision that have been followed by federal courts as a result of the construction of § 34 in Swift v. Tyson and since; after discussion, it declares (pp. 77-78) that "the unconstitutionality of the course pursued [meaning the rule of decision Opinion of REED, J. 304 U.S. resulting from that construction] compels" abandonment of the doctrine so long applied; and then near the end of the last page the Court states that it does not hold § 34 unconstitutional, but merely that, in applying the doctrine of Swift v. Tyson construing it, this Court and the lower courts have invaded rights which are reserved by the Constitution to the several States. But, plainly through the form of words employed, the substance of the decision appears; it strikes down as unconstitutional § 34 as construed by our decisions; it divests the Congress of power to prescribe rules to be followed by federal courts when deciding questions of general law. In that broad field it compels this and the lower federal courts to follow decisions of the courts of a particular State. I am of opinion that the constitutional validity of the rule need not be considered, because under the law, as found by the courts of Pennsylvania and generally throughout the country, it is plain that the evidence required a finding that plaintiff was guilty of negligence that contributed to cause his injuries and that the judgment below should be reversed upon that ground. MR. JUSTICE MCREYNOLDS concurs in this opinion. I concur in the conclusion reached in this case, in the disapproval of the doctrine of Swift v. Tyson, and in the reasoning of the majority opinion except in so far as it relies upon the unconstitutionality of the "course pursued" by the federal courts. The "doctrine of Swift v. Tyson," as I understand it, is that the words "the laws," as used in § 34, line one, of the Federal Judiciary Act of September 24, 1789, do not include in their meaning "the decisions of the local tribunals." Mr. Justice Story, in deciding that point, said (16 Pet. 19): "Undoubtedly, the decisions of the local tribunals upon such subjects are entitled to, and will receive, the most deliberate attention and respect of this Court; but they cannot furnish positive rules, or conclusive authority, by which our own judgments are to be bound up and governed." To decide the case now before us and to "disapprove" the doctrine of Swift v. Tyson requires only that we say that the words "the laws" include in their meaning the decisions of the local tribunals. As the majority opinion shows, by its reference to Mr. Warren's researches and the first quotation from Mr. Justice Holmes, that this Court is now of the view that "laws" includes "decisions," it is unnecessary to go further and declare that the "course pursued" was "unconstitutional," instead of merely erroneous. The "unconstitutional" course referred to in the majority opinion is apparently the ruling in Swift v. Tyson that the supposed omission of Congress to legislate as to the effect of decisions leaves federal courts free to interpret general law for themselves. I am not at all sure whether, in the absence of federal statutory direction, federal courts would be compelled to follow state decisions. There was sufficient doubt about the matter in 1789 to induce the first Congress to legislate. No former opinions of this Court have passed upon it. Mr. Justice Holmes evidently saw nothing "unconstitutional" which required the overruling of Swift v. Tyson, for he said. in the very opinion quoted by the majority, "I should leave Swift v. Tyson undisturbed, as I indicated in Kuhn v. Fairmont Coal Co., but I would not allow it to spread the assumed dominion into new fields." Black & White Taxicab Co. v. Brown & Yellow Taxicab Co., 276 U. S. 518, 535. If the opinion commits this Court to the position that the Congress is without power to declare what rules of substantive law shall govern the federal courts, |