As has already been suggested, although there is no direct prohibition of the taking by state or federal authorities of private property for other than public use, such a taking would be contrary to the principles of constitutional government, and prohibited by the provision as to due process of law, so that the question, What is a public purpose, is fundamental; and if it appears that the purpose of the taking is not a public purpose, the attempt of the government to take will be futile. The purposes which have been held to be sufficiently public are those for which the state or the federal government may own property to be used in a discharge of its public functions, or to be held as charged with a public use. Thus private property may be taken to furnish sites for public buildings, to provide for streets and highways, parks and other public grounds; to provide the sources and channels for water supplies for cities; to provide cemeteries in which the dead may be buried; to provide outlets for the drainage of swamps which should be drained or otherwise cared for in the protection of the public health; to provide wharves and landing places necessary for the public use in connection with navigable waters; to facilitate the improvement of streams by locks and dams so as to promote public navigation. All these and many others analogous to them are purposes for which private property may be appropriated under the power of eminent domain. So the federal government may take land for post-offices and other buildings, for forts, arsenals, and navy yards and for other uses of that government (Kohl v. United States).

Cities, counties, school districts, and other municipal and quasi-municipal corporations which exercise by delegation some of the powers of government requiring the use of property, may be authorized to take under the power of eminent domain; and such public corporations may be authorized to carry on operations such as supplying water or light or transportation for which private property may be necessary and may be justly appropriated in proper proceedings. Indeed, it may be safely said, that anything which the government or any of its branches is authorized to do requiring the use of property affords proper occasion for the exercise of the power of eminent domain.

But the government may exercise some of its functions and secure to the public some of the benefits to which the people are reasonably entitled, by delegating authority to private or corporate agencies. Thus the government may properly furnish facilities for transportation of person or property, and in doing so, it may establish and improve streets and highways; but it may authorize means of transportation, as by railways, ferries, canals, and the like, to be provided by private persons or by corporations, immediately for their own profit but ultimately for the public good. So cities, instead of directly supplying water and light to their inhabitants, may be authorized to grant franchises for waterworks and lighting plants, to corporations which derive revenue from furnishing to the public facilities which the municipal government might directly furnish if the legislature should so provide. It is with reference to these public utility corporations, as they have been called, that the greatest difficulty has been experienced in determining the extent to which the government may go in authorizing the taking of private property for public uses; but it may be regarded as reasonably well settled that if the government authorizes a private person or corporation to render services to the public which the government might render for itself if it saw fit so to do, it may confer upon such person or corporation the power to take private property without the owner's consent on making compensation, so far as reasonably necessary to the performance of the public functions thus delegated. Accordingly it is now well settled that railroad companies may be authorized to take land for right of way, depot grounds, and other necessary purposes (Cherokee Nation v. Kansas R. Co.); that telegraph companies may by proper proceedings acquire the right to construct lines through private property; that one who desires to establish a public ferry across a river may be authorized to condemn such land as is necessary for landing places on the opposite sides of the stream; that a corporation desiring to erect a toll-bridge may be authorized to condemn land required for abutments and piers; that a corporation authorized to furnish water to the residents of a city may be empowered to condemn the land essential for establishing its plant and laying its pipes.

The taking of private property for the utilization and improvement of water power is also regarded as a purpose for which private property may be condemned. Thus a person having acquired the right to construct a dam across a stream to secure power for the operation of a mill or other manufacturing purpose may by condemnation acquire the right to flood the lands of private owners by thus damming the stream (Pumpelly v. Green Bay Co.) The right to thus practically confiscate private property in order to utilize water power for private purposes rests on peculiar grounds. It can hardly be said that the purpose is public in any sense, and yet, if water power is a public resource of which individuals may be allowed to avail themselves, it is perhaps not unreasonable to say that they may be permitted to damage the property of other individuals, on making just compensation, as far as is necessary to render such water power available.

As distinct from these uses which are clearly public in their nature, other uses incidentally advantageous to the public but primarily for individual benefit have been held to be private uses for which property cannot be taken without the consent of the owner. The establishment of a manufactory may be incidentally of public benefit to those living in a particular locality, but the property devoted to such use nevertheless remains private property and the purpose is not one justifying a compulsory taking.

It is to be noted that in all the cases where individuals or private corporations are authorized to condemn private property for their uses, the nature of the business which they are to carry on involves appropriation of specific property so peculiarly situated with reference to the undertaking that other like property could not be substituted for it; and therefore, if the individual or corporation could not compel the owners of such specific property to allow its appropriation, the enterprise might be defeated by the unreasonable demands of such private owners. There are many other uses to some extent public for which private property cannot be taken because the enterprise does not necessarily involve the use of one piece of property rather than another. But after all, these considerations affect more directly the expediency of authorizing private individuals or corporations to take the property of others, and it may, perhaps, safely be said that conceding the purpose to be public, the question whether an individual or corporation shall be allowed to condemn private property for such purposes is a matter of legislative discretion.

Another illustration of what may properly be deemed a public purpose is furnished by cases involving the right to establish private roads. As a general proposition, lands may be taken on which to locate public highways; while on the contrary a mere right of way by which the individual is benefited is not such a purpose. But in order to operate coal mines, stone quarries, oil and gas wells, and other like works for making available the natural resources of particular portions of the earth's surface, it is necessary that an outlet be secured to highways, railways, navigable streams, or other public avenues of transportation. Therefore a roadway or railway or canal or pipe line specifically intended to furnish necessary facilities to the individual or corporation operating the mine, quarry, or well, while it is primarily for his benefit, nevertheless may be for a public purpose to such an extent that the right to pass over or through private property may be taken therefor.