The following cmavo is discussed in this section:
ni 
NU 
amount abstraction 
Amount abstractions are far more limited than event or property abstractions. They really make sense only if the selbri of the abstracted bridi is subject to measurement of some sort. Thus we can speak of:
le  ni  le  pixra  cu  blanu  [kei] 
the  amountof  (the  picture  beingblue  ) 
the amount of blueness in the picture 
because “blueness” could be measured with a colorimeter or a similar device. However,
le  ni  la  .djein.  cu  mamta  [kei] 
the  amountof  (thatnamed  Jane  beingamother  ) 
the amount of Jane's motherness (?) 

the amount of motherness in Jane (?) 
makes very little sense in either Lojban or English. We simply do not have any sort of measurement scale for being a mother.
Semantically, a sumti with le ni is a number; however, it cannot be treated grammatically as a quantifier in Lojban unless prefixed by the mathematical cmavo mo'e :
li  pa  vu'u  mo'e  le  ni  
thenumber  1  minus  theoperand  the  amountof  ( 
le  pixra  cu  blanu  [kei] 
the  picture  beingblue  ) 
1  B
, where

Mathematical Lojban is beyond the scope of this chapter, and is explained more fully in Chapter 18.
Whenever we talk of measurement of an amount, there is some sort of scale, and so the place structure of ni abstraction selbri is:
ni x_{1} is the amount of (the bridi) on scale x_{2}
Note: the best way to express the x_{2} places of abstract sumti is to use something like le ni ... kei be. See Example 11.59 for the use of this construction.