The answer is this: American government, both in the nation and in the states, rests upon certain fundamental rules which are embodied in written constitutions. These rules determine, among other things, the powers and functions of government officers and bodies, including Congress and the legislatures. They have been placed in the national and state constitutions with the intent that they shall be obeyed, and if they were not obeyed one branch of the government would be encroaching upon the powers of the other. But how can powerful bodies like Congress and the state legislatures be held to the obedience of rules laid down in the national constitution? The Supreme Court performs this duty by declaring “unconstitutional” any law which, in its judgment, violates the provisions of that document. The constitution, for example, provides that Congress shall pass no bill of attainder. If Congress should enact a measure of that kind, the court would nullify it. The constitution stipulates that no state shall make any law impairing the obligations of contract. If any state legislature should enact such a law, the Supreme Court would declare it to be unconstitutional and void. [Sidenote: Limitations upon the discretion of the court.] Now this does not mean that the justices of the Supreme Court have the right to veto any measure at their discretion. They have nothing to do with the merits of a measure, nothing to do with the question whether it has been wisely passed. The only issue they decide is whether a law conforms to the provisions of the constitution. If they find that it does not, they have authority to set it aside. And so long as government is based upon written constitutions there must be some body with power to decide whether a law is constitutional or not. Every branch of the government is under a natural temptation to extend its own authority. State legislatures would like to have a share in regulating the trunk railroads; Congress would like to decide how much money may be spent by candidates for senatorial nominations. Both of them have tried to extend their authority in these directions during the past few years although the constitution does not warrant their so doing. We must have some body, therefore, endowed with the right to say to all public officials and legislative bodies: “Thus far shall you go and no further; here is the point where your authority, under the constitution, comes to an end.” [Sidenote: The Supreme Court’s power is essential.]