Congress is restricted, in passing laws, necessary to carry into execution the powers expressly delegated.
But the law must, also, be proper as well as necessary, in order to bring it within its competency. To understand the true import of the term in this connection, it is necessary to bear in mind, that even the implied powers themselves are subject to important conditions, when used as means to carry powers or rights into execution. Among these the most prominent and important is, that they must be so carried into execution as not to injure others; and, as connected with, and subordinate to this — that, where the implied powers, or means used, come in conflict with the implied powers, or means used by another, in the execution of the powers or rights vested in it, the less important should yield to the more important — the convenient, to the useful; and both to health and safety — because it is proper they should do so. Both rules are universal, and rest on the fundamental principles of morals.
Such is the true import of the term "proper," superadded to "necessary," when applied to this important question. And hence, when a law of Congress, carrying into execution one of the delegated powers, comes into conflict with a law of one of the States, carrying its reserved powers into execution, it does not necessarily follow that the latter must yield to the former, because the laws made in pursuance of the constitution, are declared to be the supreme law of the land: for the restriction imposed by the term "proper," takes it out of the
