Page:Joseph Story, Commentaries on the Constitution of the United States (1st ed, 1833, vol I).djvu/464

 424 the rare and difficult scheme of one general government, whose action extends over the whole, but which possesses only enumerated powers, and of numerous state governments, which retain and exercise many powers not delegated to the Union, contests respecting power must arise. Were it even otherwise, the measures taken by the respective governments to execute their acknowledged powers would be often of the same description, and might sometimes interfere. This, however, does not prove, that the one is exercising, or has a right to exercise, the powers of the other.

§ 439. And this leads us to remark, that in the exercise of concurrent powers, if there be a conflict between the laws of the Union and the laws of the states, the former being supreme, the latter must of course yield. The possibility, nay the probability, of such a conflict was foreseen by the framers of the constitution, and was accordingly expressly provided for. If a state passes a law inconsistent with the constitution of the United States it is a mere nullity. If it passes a law clearly within its own constitutional powers, still if it conflicts with the exercise of a power given to congress, to the extent of the interference its operation is suspended; for, in a conflict of laws, that which is supreme must govern. Therefore, it has often been adjudged, that if a state law is in conflict with a treaty, or an act of congress, it becomes &apos;ipso facto&apos; inoperative to the extent of the conflict.