122 
POLITICAL ECONOMY 
even this proposition, defining the principle 
on which gold is distributed between money 
and the arts, is not, when stated in general 
terms, peculiar to the doctrine of money. 
It holds of all cases where demand is com 
posite. To take again our previous example, 
wood would be so distributed between house 
building, furniture-making, and boat-building, 
that the marginal utilities of wood for all these 
purposes would be the same. 
In order to bring the theory of money 
exactly into line with the theory of the prices 
of things, it must finally be remarked that 
what is designated purchasing-power in the 
case of money corresponds with what is 
designated price in the case of other things. 
Media of exchange cannot have a price proper, 
that is an exchange value in terms of money, 
because the exchange value of a thing cannot 
be expressed in terms of itself. But the 
price of a thing means the amount of money 
that it will buy, because the price is the amount 
of money which will buy it, and exchange is 
a simply convertible relation. Now what a 
unit of money will buy is called its purchasing 
power. Consequently, employing the term 
“ price ” broadly, to indicate exchange value 
and not merely exchange value in money, we 
may say that the purchasing power of money