RENT

213

theory  of  rent,  which  holds  in  this  particular
case,  holds  also  of  payments  for  differential
advantages  of  quite  another  kind.  The
foregoing  demonstration  is  in  fact  an
exposition  by  the  method  of  example  of  the
general  theory  of  rent  when  rent  is  understood
as  payment  for  differential  advantages.  It
will  be  comprehended  that  the  same  forces
come  into  play  when  human  factors  in
production  are  being  dealt  with  as  well  as
when  land  is  being  dealt  with.  Just  as  there
are  differences  in  respect  of  fertility  between
different  plots  of  land,  so  there  are  differences
in  respect  of  capacity,  industry  and  quickness
between  different  persons.  Take  the  case
of  a  particular  industry,  and,  to  make  it  a
strong  case,  suppose  that  those  who  work  in
it  must  have  special  ability.  Naturally  it  is
impossible  to  obtain  for  the  industry  an
unlimited  supply  of  labour  of  the  highest
quality.  Employers  must  have  recourse  to
labour  of  lower  qualities  if  the  trade  is  to
attain  to  any  magnitude,  just  as  farmers
must  have  recourse  to  some  land  which  is  not
of  the  best  sort.  The  least  efficient  operative
may  be  termed  the  marginal  operative,  just
as  the  least  valuable  land  may  be  termed  the
marginal  land.  Through  the  working  of  the
principle  of  substitution  it  is  plain  that  the