In  the  moral  and  political  sciences,  including
political  economy,  classification  is  beset  with
peculiar  difficulties  and  dangers.  The  most
obvious  of  these  lies  in  the  fact  that  none  of
these  sciences  possesses,  or  is  ever  likely  to
possess,  a  complete  scientific  vocabulary,  the
terms  of  which  have  the  same  precise  sense  for
every  student,  whilst  they  remain  undefaced  by
loose  popular  use.  Classification  is  at  every
step  dependent  upon  nomenclature  ;  and  it  is
only  in  sciences  which,  like  botany,  possess  a
complete  and  precise  technical  nomenclature
that  classification  can  be  carried  out  to  the
utmost  extent.  But  a  more  serious  hindrance
to  classification  is  to  be  found  in  the  nature  of
the  subject-matter  of  moral  and  political  science.
Their  subject-matter  is  far  more  complex  than
the  subject-matter  of  botany  or  zoology.  If  it
be  true  that  practically  every  individual  in  the
vegetable  or  animal  kingdom  embodies  a  more
or  less  considerable  variation  from  a  type,  how
much  more  is  this  true  of  every  human  being
and  of  every  human  institution.  Anybody
who  compares  with  the  classifications  of  natural
science  the  ^classifications,  say,  of  feelings  or
motives  in  a  treatise  of  psychology,  wiU  feel
how  much  less  adequate  is  the  latter  to  the
object  aimed  at  by  the  writer.  And  in  the
study  of  society  Mr.  Herbert  Spencer's  De-
scriptive Sociology  affords  a  striking  example  of
the  difficulties  which  beset  classification  and  of
the  limited  advantages  to  be  derived  from  it.
When  we  look  closely  into  ideas  or  institutions
which  at  first  sight  appear  very  similar,  we
usually  find  diff'erences  of  a  momentous  nature.
