THE A B C OF TAXATION •4 but it is of far greater importance to understand clearly what is the source of ground rent, and especially to what extent it may be regarded as a social product. Inasmuch as all the contributions representing these activities, so far as enumerated, are from the treasuries of the people, it is correct and proper to say that ground rent is chiefly and peculiarly a social product. From one point of view (that of demand) it may be said that the value of all commodities is a social product. But when we come to consider the other side of the value problem, we find that most other commodities, e. g., houses, increase or decrease at man’s will, according to the principle of cost, the value being a resultant of a balancing of social desire against social cost. With land it is more generally true that the quantity either cannot be increased at all or can be increased only at increasing cost; and hence the practical determinant of the value of land is almost entirely in the social and private activities that make the use of land desirable. VI.—The Maintenance of Ground Rent So far as the cost of streets, lights, water, sewerage, fire, police, schools, libraries, museums, parks, play-grounds, steam and electric railways, gas and electric lights, telegraph and telephone companies, subways, ferries, churches, private schools, colleges, universities, public buildings, well appointed houses, stores, and office buildings is what constitutes the cost value of the land, just so far the maintenance of all this public or