of  a  priori  science  are  but  an  analysis  of  the  ideas
we  already  possess,  how  is  it  that  by  reason  of  them
we  acquire  fresh  knowledge,  and  become  informed
of  that  of  which  we  were  ignorant  before  ?  It  seems
that  we  should  never  advance  by  sciences  which  add
nothing  from  outside  to  our  store  of  knowledge.
This  objection  is  solved  by  the  distinction
between  implicit  and  explicit  knowledge.  Explicit
knowledge  is  that  knowledge  which  we  possess  in
itself,  and  of  the  possession  of  which  we  are  fully
conscious.  Implicit  knowledge  is  that  knowledge
which  is  contained  in,  or  is  deducible  from,  know-
ledge already  possessed  by  us ;  but  which  we  do  not
yet  realize  as  existing  in  our  minds.  We  have  not
yet  deduced  it  from  its  premisses,  or  become  aware
of  its  reality.
To  take  a  familiar  instance.  •  I  have  often
asserted  the  proposition,  nay,  I  regard  it  almost  as
a  truism,  that  All  animals  are  possessed  of  feeling.
My  acquaintance  with  zoology  has  moreover  taught
me  that  All  jelly-fish  are  animals.  These  two  pro-
positions exist  side  by  side  in  my  intelligence.
