The purposes for which the power of state taxation may be exercised are as limitless in their variety as the special objects for which laws may be passed. Nor is the exercise of such power restricted to the general legislative department of the state government. It may be delegated to subordinate tribunals or legislative bodies such as the boards of supervisors of counties, the councils of cities, the trustees of towns or townships or school districts and the like; and the purposes extend from providing for the general expenses of the state government down to the support of the smallest branches of the local government.

An indispensable characteristic, however, of every exercise of the power, whether original or delegated, is that the purpose for which money is raised by taxation be a public purpose, that is, a purpose properly incident to the exercise of the powers of government. The legislature cannot authorize the collection of money to be expended for the private benefit of individuals. Difficult as it may be to determine whether any specific purpose is public, as distinguished from a private purpose, that distinction when properly applied will determine whether the money to be expended may properly be raised by means of taxation. It is sometimes said that the levying of taxes for a purpose not public is the taking of private property for private use, or for public use without just compensation, and contrary, therefore, to the provisions of the state and federal constitutions regulating the exercise of the power of eminent domain. But the power of eminent domain and the power of taxation are wholly distinct and independent powers. They have this in common: that each of them, in the nature of things, can be exercised for a public purpose only; and it is sometimes pertinent in determining whether the purpose is one for which the power of taxation can be exercised, to consider whether it is one for which private property may be taken without the consent of the owner.

The purposes of taxation may, however, be either general or special. General taxes may be collected to provide a general fund from which the expenses of state, county, or city government may be met, and such purposes are unquestionably public, so that no controversy can very well arise on that point. Taxes may also be levied for specific purposes, and the validity of such a tax may depend, therefore, on whether the specific purpose is a public purpose. Questions of this character do frequently arise, and their solution is often difficult, but it may safely be stated, as a general proposition, that if the purpose for which a specific tax is levied is not a public purpose, or if an attempt is made to incur a specific indebtedness for a purpose not public, which indebtedness can only be met by taxation, then the specific tax or indebtedness will be held invalid. The general ground on which such legislation is declared invalid is that it amounts to depriving persons of their property without due process of law; for the guaranty of due process of law relates not only to the method, but also to the purpose for which private property may be taken under the exercise of the power of government. This phase of the taxing power will be made the subject of consideration in a subsequent section.

It is pertinent here to observe, however, that though taxes can only be levied for a public purpose where the purpose is express or specific, appropriations of public money are not thus limited by any constitutional provision. They should be for a public purpose, but the decision as to what is a public purpose lies largely in the discretion of the legislative department; and no citizen has such direct interest in the matter that he can call in question the propriety of appropriations made from the general funds. But where the tax is specific, or the statute authorizes the incurring of indebtedness for a specific purpose which can be met only by the raising of money by a special tax, the persons whose property is subject to be taken for raising such tax may usually question the legality of the tax or indebtedness by appealing to the courts.