INTRODUCTORY

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tion.  Our  object  is  to  bring  out  the  stresses
and  strains  which  broadly  account  for  things
as  they  are.  We  only  fully  explain  a  thing
when  we  have  completely  isolated  all  relevant
and  appreciable  tendencies  at  work,  and
estimated  their  several  influences.  But  behind
many  of  the  things  to.be  explained  we  discover
a  complicated  system  of  tendencies  within
tendencies,  some  of  which  are  long  in  bringing
about  their  effects,  and  some  of  which  would
produce  their  effects  in  a  short  time  were
they  not  counteracted.  In  economics  it  is
convenient,  therefore,  to  distinguish  between
immediate  tendencies,  short  period  tendencies,
and  long  period  tendencies.  The  first  are
predominantly  effective  as  regards  immediate
results.  The  second  are  those  which  are  comparatively ­
  speedy  in  their  operation.  The
third  are  the  tendencies  remaining.  When
in  economics  we  ask  what  is  the  effect  of  a
given  cause  we  may  mean  by  the  effect,  the
immediate  effect,  the  short-period  effect,  or
the  long-period  effect.  Let  us  take  to  illustrate ­
  the  distinction  a  particular  example.
If  the  demand  for  steel  increased,  the
immediate  effect  on  price  would  be  the
resultant  rise  in  the  price  of  steel  while
the  agents  in  production  were  left  exactly
as  they  were.  The  short-period  effect  would