44 NATURE OF CAPITAL AND INCOME [Caar. II 
satisfactions from those goods are held. But the two are 
none the less distinct. It is with utility or desirability 
that we are concerned in this chapter. 
§ 4 
The desirability of any particular goods may relate to 
the whole or to any part of the group of goods. The de- 
sirability of the entire group is called the total desirability; 
the desirability of one unit more Or less of the group is 
called the marginal desirability. In economic science we 
have to do more with marginal than with total desirability, 
and it is important that the concept of marginal desir- 
ability should be thoroughly understood. 
That marginal desirability is the desirability of one unit, 
more or less, may be illustrated as follows: If a person 
airs, their marginal desirability is the differ- 
the desirability of having ten 
f having nine chairs; that is, 
it is the desirability sacrificed by having one chair less. 
Or, what is almost the same thing, the marginal desirability 
of the group of ten chairs is the desirability of one chair 
more, — the difference in desirability between eleven chairs 
and ten. Whether the marginal desirability is taken as 
referring to one unit more or to one unit less is usually of 
so little importance as not to require separate designations 
to distinguish them, and in case the commodity is one which 
admits of indefinite subdivision, as flour, wheat, coal, etc., 
the two coalesce as the size of the increment is reduced in- 
definitely.! This fact is usually expressed by saying that 
the marginal desirability of the chairs is the desirability of 
“the tenth’ chair. But though this mode of statement is 
correct, it is not intended to convey the idea that any par- 
ticular chair is the “tenth” chair. 
The group of goods the marginal desirability of which is 
under consideration may be any specified group of goods 
1 For a mathematical treatment see Appendix to Chap. III, § 1. 
possesses ten ch 
ence, in his mind, between 
chairs and the desirability o