SUPPLY  AND  DEMAND

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and  constant  returns  must  not  be  confounded
with  the  so-called  laws  of  increasing,  decreasing, ­
  and  constant  returns.  Let  us  confine
our  attention  for  the.  moment  to  increasing
returns  and  remember  that  all  that  is  affirmed
about  it  applies  mutatis  mutandis  to  decreasing
and  constant  returns.  The  conception  of
increasing  returns  has  been  explained.  Now
the  law  of  increasing  returns  is  best  interpreted,
in  my  opinion,  as  defining  the  conditions  under
which  increasing  returns  with  reference  to
industries  are  met  with.  There  is  not  yet
among  economists  complete  agreement  upon
this  matter  ;  but  in  a  brief  introduction  to
economic  theory  I  must  be  content  to  put  forward ­
  my  own  views,  which  are  those  of  others
also,  as  regards  the  most  appropriate  interpretation, ­
  while  warning  the  reader  that  they
are  not  universally  accepted  I  should  take  it,
then,  that  the  law  of  increasing  returns  defines
the  conditions  under  which  increasing  returns
are  met  with  in  industries.  These  conditions
can  be  easily  formulated,  but  we  may  formulate ­
  them  at  different  levels  of  abstraction  ;
and  it  goes  without  saying  that  the  more
complete  the  abstraction  the  more  universal
will  the  law  be.  It  will  probably  be  a  convenience ­
  to  recognise  two  laws,  namely,  the
abstract  law  and  the  realistic  law.  I  shall