The reasonableness of the agency of the national courts in cases in which the state tribunals cannot be supposed to be impartial, speaks for itself. No man ought certainly to be a judge in his own cause, or in any cause in respect to which he has the least interest or bias. This principle has no inconsiderable weight in designating the federal courts as the proper tribunals for the determination of controversies between different states and their citizens. And it ought to have the same operation in regard to some cases between citizens of the same state. Claims to land under grants of different states, founded upon adverse pretensions of boundary, are of this description. The courts of neither of the granting states could be expected to be unbiased. The laws may have even prejudged the question, and tied the courts down to decisions in favor of the grants of the state to which they belonged. And even where this had not been done, it would be natural that the judges, as men, should feel a strong predilection to the claims of their own government.
Having thus laid down and discussed the principles which ought to regulate the constitution of the federal judiciary, we will proceed to test, by these principles, the particular powers of which, according to the plan of the convention, it is to be composed. It is to comprehend “all cases in law and equity arising under the Constitution, the laws of the United States, and treaties made, or which shall be made, under their authority; to all cases affecting ambassadors, other public ministers, and consuls; to all cases of admiralty and maritime jurisdiction; to controversies to which the United States shall be a party; to controversies between two or more states; between a state and citizens of another state; between citizens of different states; between citizens of the same state claiming lands and grants of different states; and between a state or the citizens thereof and foreign states, citizens, and subjects.” This constitutes the entire mass of the judicial authority of the Union. Let us now review it in detail. It is, then, to extend: