46 NATURE OF CAPITAL AND INCOME  [Cuar. III 
marginal desirability of the windows is the desirability of 
the fiftieth window, or the difference in the desirability 
of having fifty windows rather than forty-nine. 
§5 
The first principle in regard to marginal desirability 
is that an increase in the quantity of goods in the group 
the marginal desirability of which is under consideration, 
results in a decrease in the marginal desirability of the 
group. Each successive increment is less desirable than 
the preceding increment. The marginal desirability of 
sugar to the householder consuming five pounds weekly is 
greater than the marginal desirability if six pounds are con- 
sumed, and is successively diminished as each successive 
pound is added to his consumption. 
It is well to remember that when the term “successively” 
is here employed, it is not used in a temporal sense. The 
succession to which it refers is not a succession in time, but 
a succession in thought. We consider the consumer of 
sugar under a series of different hypotheses which we 
examine successively. We begin with the hypothesis of 
a weekly consumption of five pounds, and take up succes- 
sively the hypotheses of six pounds, seven pounds, eight 
pounds, ete. The desirability of the “last” pound in this 
series is the marginal desirability for the group ending at 
that point; but the “last” pound refers to the one consid- 
ered last in our mental review, and not the one acquired last 
by the consumer. This fact needs to be emphasized, in 
view of frequent confusion on the subject occasioned by too 
Joose an employment of the words “last” and “ successive.” 
It is presumably because of the time confusions involved 
in these words that, under the leadership of Wieser® and 
Marshall? economists have substituted the phrase ‘“mar- 
ginal utility” for the older phrase of Jevons, “final utility.” 
With these provisos and explanations in view, it is clear 
 Ursprung des Werthes, p. 128. 
? Principles of Economics, 3d ed., 1895, p. 168.