G 
MONOPOLY 
97 
receipts, provided that an addition to the 
output at this point would cause marginal 
costs to exceed differential receipts, and a 
reduction of the output would cause differ 
ential receipts to exceed marginal costs. 
By marginal costs is to be understood the 
addition made to aggregate costs by the 
production of the last increment ; and by 
differential receipts is to be understood the 
addition made to the aggregate gross receipts 
by the sale of the last increment. We must 
not call the latter “ marginal receipts,” 
because that term might mean the marginal 
demand price. It is necessary to remark that 
there may be outputs other than that yielding 
the greatest monopoly revenue of which 
the above statement holds. Any position of 
which it holds may be called a position of 
monopoly equilibrium. When there is more 
than one position of monopoly equilibrium, 
so defined, the monopolist naturally selects 
that one which yields him the highest 
monopoly revenue, provided that he knows 
of its existence. 
Thus far we have taken for granted that 
the commodity can be sold for one price only, 
but as we shall see later there are circum 
stances in which it is feasible to impose 
differential or discriminative charges. How-