DEMAND

89

articles  or  services,  total  utility  means  the
loss  of  satisfaction  which  would  be  sustained  by
the  complete  withdrawal  of  that  commodity
or  service,  while  the  marginal  utility  means
the  addition  made  to  our  total  satisfaction
by  the  acquisition  of  the  last  increment  of
the  commodity  or  -service.  The  diminution
spoken  of  in  the  law  of  diminishing  utility
refers  to  marginal  and  not  to  total  utilities;
though  total  utilities  may  themselves  contract
when  people  are  encumbered  with  things  of
which  they  want  no  more,  in  which  case
marginal  utilities  are  said  to  have  become
negative.
We  are  now  in  a  position  fully  to  grasp
the  conception  of  demand.  We  are  said  to
demand  a  thing  when  we  are  prepared  to  offer
something  of  value  for  it.  When  the  offer
is  made  in  terms  of  money  the  offer  is  said  to
be  a  demand  price.  Now  it  will  be  apparent
that  a  person  will  buy  more  of  a  thing  when
the  price  falls.  In  ordinary  circumstances,
since  the  marginal  utility  of  a  thing  drops
when  a  person  gets  more  and  more  of  it,
price  must  be  diminished  if  he  is  to  be  induced
to  purchase  larger  quantities.  Thus,  were  the
price  of  tea  18s.  a  pound,  I  would  buy  only
one  pound  a  year,  say  ;  but  if  the  price  were