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POLITICAL  ECONOMY

price.  It  is  extremely  important  to  observe  that
this  theory  in  its  bearing  on  employed  factors
does  not  declare  that  each  agent  gets  what  it
makes,  but  merely  that  each  agent  gets  the
difference  that  it  makes  to  the  total  output
of  a  productive  group  which  is  organized  to
work  as  a  whole.  Finally,  to  complete  the
theory  we  have  the  doctrine  of  rent  which
accounts  for  payments  made  on  behalf  of
agents  which  enjoy  differential  advantages.
It  needs  no  specific  intimation  that  in  this
theory  it  is  marginal  incidents  that  play  the
leading  parts,  just  as  it  was  marginal  incidents
which  enabled  us  to  comprehend  fully  the
phenomena  of  price.  Now,  in  relation  to
price,  we  observed  that  an  incisive  application ­
  of  the  marginal  method  on  the  side
of  demand  brought  out  a  novel  feature
known  as  consumer’s  surplus  ;  and  it  remains
to  investigate  whether  a  similar  feature  may
not  be  revealed  on  the  side  of  supply.  It  may
be  said  at  once  that  a  similar  feature  will  be
found  to  exist.  It  is  called  producer’s  surplus.
Broadly  put  consumer’s  surplus  stands  for
the  difference  between  the  value  that  a  consumer ­
  gets  from  a  thing  and  the  value  that
he  gives  for  it  when  he  purchases  it.  Then,  to
be  strictly  analogous,  producer’s  surplus
should  stand  for  the  difference  between  the