(2) From _price equivalents_ to _market-price_. The price at which a given supply of a certain good can be sold to a body of consumers is a _resultant_ from their individual price equivalents for this good. It is in no sense an average or mean of these price equivalents.[223] This is best understood by imagining the supply of the good offered in the market to be increased by one unit. This extra unit must be added to some person’s stock. It will go normally to the person who will pay the most for it, but the price of the unit will have to be lowered sufficiently to bring it down to this person’s price equivalent for a unit. In the open market, then, the prices of all units will have to be lowered to the level of the price of this unit. This illustrates the way in which the social demand price of a given supply of goods is determined at some individual price equivalent. The price of a given supply is determined at the point of a marginal individual price equivalent. In the last section it was asserted that unless a good is possessed in a plurality of units, that is, in a _stock_, by the individual consumer, its value will not be determined by _marginal_ utility. The Austrian writers have made this perfectly clear, but there are innumerable places in the literature which has sprung up about the Austrian theory, either expounding or criticizing it, where the value of such a good as a piano or a furnace is said to depend on marginal utility. Let us suppose that no person possesses more than one piano. In this case, properly speaking there is nothing marginal about the value-determining utility of a piano. There are, however, two methods in vogue of discovering an alleged marginal utility in such a single unit commodity. The first is to point out that a piano may serve several uses. For instance, it may be used to produce music and also as an ornamental piece of furniture. It is then suggested that one of these uses is greater or less than the other and is marginal. Some suggest by implication or directly that it is the least use to which a piano is put which determines its value to the owner. If it should be suggested in reply that a piano might be used to conceal a discolored place in the wall, which could equally well be done by a two-dollar screen, the probable reply would be that it is only the least use to which the piano can be put _economically_ which determines its value. Even so acute a writer as Smart[224] is guilty of this perversion. When it is in the pursuit of such margins, the mind is far adrift from the true logic of the utility theory. When a piano is actually used to cover a piece of wall, this is assuredly an “economic” use of the article. This use does not exclude or hamper any of its other uses. It is true no one would pay $600 for a piano merely to cover a bad piece of wall, but very likely few would pay that sum for any one use of the piano. The truth is, the value of a piano to its user depends upon