48 
POLITICAL ECONOMY 
of the subtlest generalisations wrung by 
Dr. Marshall out of the facts of experience 
after analysing them to the last dregs by the 
marginal method. The conception is known 
as that of consumers’ surplus. 
Consumers’ surplus has been used in two 
ways : to indicate on the one hand a surplus 
of utility and on the other hand the expression 
of this in terms of money. The “ surplus ” 
in utility obtained by an individual from 
anything, consists in the utility which he 
obtains from that thing over and above the 
product of its marginal utility and the quantity 
of it that he consumes. It is called a surplus 
because it represents a gain which, so to 
speak, the individual gets for nothing. Let 
us take a particular example. Suppose a 
person consumes a dozen apples a week. 
The price he pays for apples measures the 
difference between the utility to him of 
twelve apples and the utility to him of eleven 
apples, in short, the marginal utility of the 
apples. He buys the twelfth apple because 
he thinks it is just worth his while to do 
so. For the sake of clearness of statement 
let us say that the marginal utility of apples 
contains ten units of utility—carefully bear 
ing in mind at the same time that there are 
no such things as units of utility. Then, if