INTRODUCTORY

81

for  two  reasons.  It  is  of  value,  in  the  first
place,  because  what  actually  happens  frequently ­
  approximates  to  the  long-period
theoretical  result  though  it  never  exactly
corresponds  with  it  ;  and  in  the  second
place,  because  no  movement  can  be  understood
till  the  forces  producing  it  are  understood,
whether  a  force  is  ever  left  in  unrestrained
freedom  for  as  long  as  it  lasts  or  not.
The  economics  of  this  book  will  be  concerned
almost  exclusively  with  long-period  results.
These  results  are  known  as  normal.  In
contrast  with  them  short-period  results  are
sometimes  described  as  the  sub-normal.  The
reader  must  be  particularly  careful  not  to
fall  into  the  error  made  by  a  writer  who
complained  that  the  assumption  of  the  longperiod
  expresses  a  “  theory  of  perfectibility,”
and  implies  a  “  possible  state  of  perfection
in  the  material  world.”  He  judged  that
“  it  is  difficult  to  be  so  confident  about  the
present  trend  of  our  social  and  economic
strivings  as  to  continue  to  use  the  words
‘  in  the  long  run  ’  with  any  boisterous  hopefulness.” ­
  The  reader  will  understand  that
the  phrase  “  in  the  long  run  ”  expresses
neither  optimism  nor  pessimism,  but  simply
that  use  is  being  made  of  the  kind  of  hypothesis ­
  on  which  all  deductive  science  is  based.