It provides that Congress shall have certain legislative authority over all places purchased by the United States for certain purposes.  It implies that Congress has otherwise the power to purchase.  But where does Congress get the power to purchase?  Manifestly it must be from some other clause of the Constitution, for it is not conferred by this one.  Now, as it is a fundamental principle that the Constitution is one of limited powers, the authority to purchase must be conferred in one of the enumerations of legislative power; so that the power to purchase is itself not an unlimited one, but is limited by the objects in regard to which legislative authority is directly conferred.

The other expressions of the clause in question confirm this conclusion, since the jurisdiction is given as to places purchased for certain enumerated objects or purposes.  Of these the first great division—­forts, magazines, arsenals, and dockyards—­is obviously referable to recognized heads of specific constitutional power.  There remains only the phrase “and other needful buildings.”  Wherefore needful?  Needful for any possible purpose within the whole range of the business of society and of Government?  Clearly not; but only such “buildings” as are “needful” to the United States in the exercise of any of the powers conferred on Congress.

Thus the United States need, in the exercise of admitted powers, not only forts, magazines, arsenals, and dockyards, but also court-houses, prisons, custom-houses, and post-offices within the respective States.  Places for the erection of such buildings the General Government may constitutionally purchase, and, having purchased them, the jurisdiction over them belongs to the United States.  So if the General Government has the power to build a light-house or a beacon, it may purchase a place for that object; and having purchased it, then this clause of the Constitution gives jurisdiction over it.  Still, the power to purchase for the purpose of erecting a light-house or beacon must depend on the existence of the power to erect, and if that power exists it must be sought after in some other clause of the Constitution.

From whatever point of view, therefore, the subject is regarded, whether as a question of express or implied power, the conclusion is the same, that Congress has no constitutional authority to carry on a system of internal improvements; and in this conviction the system has been steadily opposed by the soundest expositors of the functions of the Government.

It is not to be supposed that in no conceivable case shall there be doubt as to whether a given object be or not a necessary incident of the military, naval, or any other power.  As man is imperfect, so are his methods of uttering his thoughts.  Human language, save in expressions for the exact sciences, must always fail to preclude all possibility of controversy.  Hence it is that in one branch of the subject—­the question of the power of Congress to make appropriations in aid of navigation—­there is less of positive conviction than in regard to the general subject; and it therefore seems proper in this respect to revert to the history of the practice of the Government.