The relation between the measure and the end, between the nature of the means employed towards the execution of a power, and the object of that power, must be the criterion of constitutionality; and not the greater or less of necessity or expediency.[1] If the legislature possesses a right of choice as to the means, who can limit that choice? Who is appointed an umpire, or arbiter in cases, where a discretion is confided to a government? The very idea of such a controlling authority in the exercise of its powers is a virtual denial of the supremacy of the government in regard to its powers. It repeals the supremacy of the national government, proclaimed in the constitution.
§ 1243. It is equally certain, that neither the grammatical, nor the popular sense of the word, "necessary," requires any such construction. According to both, "necessary" often means no more than needful, requisite, incidental, useful, or conducive to. It is a common mode of expression to say, that it is necessary for a government, or a person to do this or that thing, when nothing more is intended or understood, than that the interest of the government or person requires, or will be promoted by the doing of this or that thing. Every one's mind will at once suggest to him many illustrations of the use of the word in this sense.[2] To employ the means, necessary to an end, is generally understood, as employing any means calculated to produce the end, and not as being confined to those single means, without which the end would be entirely unattainable.
§ 1244. Such is the character of human language,