146. The people interpret their will in their election of executive, legislative, or judiciary, and the elective system prevails for all three in most of the States.[408] The courts interpret the laws in course of performance of their judicial duties, and their interpretation conforms to principles of justice. Thus in addition to the popular restraint, through frequent elections,—there is judicial restraint, or limitation of legislative and executive (but strictly ministerial) powers.[409] The entire case, as to the relation of the judiciary to the legislative, is covered by the rule laid down by the Supreme Court: “It is emphatically the province and duty of the judicial department to say what the law is.”[410] This duty is of State judges as well as federal, for all American judges are alike bound by oath to support the Constitution.[411] Any American judge has jurisdiction to pronounce as to the constitutionality of an act of Congress or of a State legislature. The essential fact necessary in such pronouncement is that the validity of the law is vital to the real interests of a party to the case or controversy before the court. The decision of the court is not an _obiter dictum_, a mere philosophical opinion, so-called, of the judges, individually, or collectively, based on an interpretation of justice. The constitutionality of the law in question must be an essential part of the issue before the court. Whenever, in pursuance of an honest and actual antagonistic assertion of rights by one individual against another there is presented a question involving the validity of any act of any Legislature, State or federal, and the decision necessarily rests on the competency of the Legislature to so enact, the court must, in the exercise of its solemn duties, determine whether the act is constitutional or not; but such an exercise of power is the ultimate and supreme function of courts. It is legitimate only in the last resort, and as a necessity in the determination of real, earnest, and vital controversy between individuals. It never was the thought that by means of a friendly suit, a party beaten in the Legislature could transfer to the courts an inquiry as to the constitutionality of the legislative act.[412] The principle of constitutional interpretation is given by Chief Justice Marshall: Let the end be legitimate, let it be within the scope of the Constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the Constitution, are constitutional.[413] And he develops the principle further: But where the law is not prohibited, and is really calculated to effect any of the objects entrusted to the government, to undertake (in courts of law) to inquire into the degree of its necessity would be to pass the line which circumscribes the judicial department, and to tread on legislative ground.[414]