Full Idea
Externalism about content would have the consequence that most of our knowledge of our own intentional states is indirect and must be based on external evidence.
Gist of Idea
Externalism about content makes introspection depend on external evidence
Source
Jaegwon Kim (Philosophy of Mind [1996], p.207)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.207
A Reaction
I think this is a confusion, endemic in discussions of externalism. If what Shakespeare meant by 'water' is H2O, or Putnam means by 'elm' what experts say, the point is that their meanings are NOT part of their intentional states, which are bookmarks.