But the right, with all these consequences, is not more certain than that possessed by the several States, as parties to the compact, of interposing for the purpose of arresting, within their respective limits, an act of the federal government in violation of the constitution; and thereby of preventing the delegated from encroaching on the reserved powers. Without such right, all the others would be barren and useless abstractions — and just as puerile as the right of judging, without the right of pronouncing an act to be unconstitutional, and, as such, null and void. Nor is this right more certain, than that of the States, in the same character and capacity, to decide on the mode and measure to be adopted to arrest the act, and prevent the encroachment on the reserved powers. It is a right indispensable to all the others, and, without which, they would be valueless.
These conclusions follow irresistibly from incontestable facts and well-established principles. But the possession of a right is one thing, and the exercise of it another. Rights, themselves, must be exercised with prudence and propriety: when otherwise exercised, they often cease to be rights, and become wrongs. The more important the right, and the more delicate its character, the higher the obligation to observe, strictly, the rules of prudence and propriety. But, of all the rights appertaining to the people of the several States, as members of a common Union, the one in question, is by far the most important and delicate; and, of course, requires, in its exercise, the greatest caution
