The rents of wharfage, dock, and harbor room, water-power, and many other privileges, may be analyzed on similar principles. Take the case, for example, of a patent or exclusive privilege for the use of a process by which the cost of production is lessened. If the value of the product continues to be regulated by what it costs to those who are obliged to persist in the old process, the patentee will make an extra profit equal to the advantage which his process possesses over theirs. This extra profit is essentially similar to rent, and sometimes even assumes the form of it, the patentee allowing to other producers the use of his privilege in consideration of an annual payment. The extra gains which any producer or dealer obtains through superior talents for business, or superior business arrangements, are very much of a similar kind. If all his competitors had the same advantages, and used them, the benefit would be transferred to their customers through the diminished value of the article; he only retains it for himself because he is able to bring his commodity to market at a lower cost, while its value is determined by a higher.(219) § 4. _Résumé_ of the laws of value of each of the three classes of commodities. A general _résumé_ of the laws of value, where a free movement of labor and capital exists, may now be briefly made in the following form: Exchange value has three conditions, viz.: 1. Utility, or ability to satisfy a desire (U). 2. Difficulty of attainment (D), according to which there are three classes of commodities. 3. Transferableness. Of the second condition, there are three classes: 1. Those limited in supply—e.g., ancient pictures or monopolized articles. 2. Those whose supply is capable of indefinite increase by the use of labor and capital. 3. Those whose supply is gained at a gradually increasing cost, under the law of diminishing returns. Of those limited in supply, their value is regulated by Demand and Supply. The only limit is U. Of those whose supply is capable of indefinite increase, their normal and permanent value is regulated by Cost of Production, and their temporary or market value is regulated by Demand and Supply, oscillating around Cost of Production (which consists of the amount of labor and abstinence required). Of those whose supply is gained at a gradually increasing cost, their normal value is regulated by the Cost of Production of that portion of the whole amount of the whole amount needed, which is brought to market at the greatest expense, and their market value is regulated by Demand and Supply (as in class 2). If there be no free competition between industries, then the value of those commodities which has been said, in the above classification, to depend on cost of production, will be governed by the law of Reciprocal Demand. Chapter IV. Of Money. § 1. The three functions of Money—a Common Denominator of Value, a Medium of Exchange, a “Standard of Value”.