Article I, Section 8, Clause 18:
[The Congress shall have Power . . . ] To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.
In general, Supreme Court doctrine has afforded relatively little attention to whether the word proper
as used in the Necessary and Proper Clause independently limits Congress's authority.1 Indeed, it is not clear that proper
imparts any limitation on Congress's power beyond the McCulloch test itself, which requires a law to both be appropriate
and consist[ent] with the letter and spirit of the constitution.
2 At the least, to be proper,
an act of Congress must not violate another express or implied constitutional provision, including the system of dual state-federal sovereignty established by the Constitution.3 For example, the Court has held that the Tenth Amendment operates to restrain the scope of the Necessary and Proper Clause, holding that an otherwise valid law that violates principles of state sovereignty is not a proper
exercise of federal power.4