Final answer:
John pays income taxes to both Mississippi and the federal government because taxation is a concurrent power shared by state and federal governments.
Step-by-step explanation:
The necessity of John, a resident of Mississippi, paying income tax to both the state and federal government can be explained by the concept that taxation is a concurrent power. Concurrent powers are responsibilities shared between the state and national governments because the Constitution does not explicitly reserve them for the national government exclusively or deny them to the states. Both the state of Mississippi and the federal government have the right to levy and collect income taxes from their citizens. This duality of tax collection is part of the system of federalism established by the U.S. Constitution, where both levels of government are sovereign in their respective spheres but also have areas where their responsibilities overlap.