Full Idea
The implication of considerations of Twin Earth cases is that even beliefs about the properties of kinds of stuff are implicitly indexical, or context-dependent, in character.
Clarification
'Indexical' statements depend on context for meaning
Gist of Idea
Twin Earth cases imply that even beliefs about kinds of stuff are indexical
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 4)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.82
A Reaction
This is a significant connection, between debates about the nature of indexicals (such as 'I' and 'this') and externalism about content generally. Is there no distinction between objective reference and contextual reference?