Even the monopoly is able to get different prices for different parts of its output only by offering them at different times; and competing producers cannot do this. They are forced to keep the price of all they offer at a level that expresses its final utility. _The Law of Value affected by the Difficulty of using Two Similar Goods at Once._--There are two imperfections in the common statement of this law of final utility which need to be removed in order that the theory of value, which is based on the law, may be true and useful. The first lies in the assumption that people buy completed articles, such as coats, tables, vehicles, watches, etc., in regular series of units, adding to their stock coat after coat, watch after watch, etc., all just alike, till the utility of the last one becomes so small that it is better to buy other things. On this supposition the price of the whole supply of any such thing corresponds with the utility of the last one in the consumer's series. This fairly well describes the case of commodities like apples, of which men consume now more and now less per day or per week and are always glad to increase the amount they use. Of most kinds of consumers' goods a person wants at one time one unit and no more, and a second unit, if he has to use it himself within the same time in which he uses the first, would be an incumbrance. Its utility would be a negative quantity. Two quite similar coats would never be bought by the same person if he had only his own needs in view and must use both coats through the same period. The first unit of his supply is, for this period, also the last.