can be sold
at the cost price, and there the enlargement of the output has
stopped; the supply has at some time in the past reached this normal
point and now remains there. Ten dollars represents the final utility
of the article, and this sum is what it costs to make it. If it could
be sold for any more than that, competition would bring new producers
into this business and would impel those already in it to enlarge
their production till the price would stand at the normal or cost
level of ten dollars.

_The Consumers' Surplus._--In every such case there are men who would
give much more for the article rather than be without it, and we have
supposed that some one would pay a hundred dollars for this commodity
if he could not otherwise obtain it. Ninety dollars, then, measures
what we may call his _consumers' surplus_, or the clear benefit he
gets from buying at its market price an article that is worth to him
so much more. This comes about by the fact that the makers of article
A, in order to sell the amount of goods that competition has impelled
them to make, must accept the offers of persons who can consistently
give only ten dollars for it. These are relatively poor persons, and
as the sum of ten dollars expended on other articles would benefit
them as much as ten dollars spent on this one, it is a "final"
purchase, or a final increment of their consumers' wealth. In order to
get it they sacrifice, in some other form, a benefit as great as the
one they get from acquiring this commodity and receive, therefore, no
consumers' surplus from it. These are the men whose demand helps to
fix the price of the article A, and the willingness of other persons
to give more does not make it bring any more. The rich men, who stand
ready to pay a hundred dollars, if necessary, are gainers by letting
poorer men fix this price. It is by catching the patronage of these
poorer men that the makers can dispose of their large output, and in
doing this they have to bring the price down to ten dollars.

_The Function of a Special Class of Marginal Purchasers of Each
Article._--In like manner there is a class of "marginal purchasers" of
the article B, or the persons who pay for it so much that they get no
net benefit or consumers' surplus from the purchase. If they did not
buy this article, they could get something else that would do them as
much good for the same outlay. It costs, let us say, only ten dollars
in the making, and enough of t