Full Idea
Contextualist semantics must capture the 'indexical' nature of knowledge claims, the fact that different utterances of a knowledge sentence with no apparent indexical terms can express different propositions.
Clarification
'Indexical' implies that meaning varies with context
Gist of Idea
Contextualism needs a semantics for knowledge sentences that are partly indexical
Source
Stephen Schiffer (Contextualist Solutions to Scepticism [1996], p.325), quoted by Keith DeRose - The Case for Contextualism 1.5
Book Reference
DeRose,Keith: 'The Case for Contextualism' [OUP 2009], p.9
A Reaction
Schiffer tries to show that this is too difficult, and DeRose defends contextualism against the charge.
Related Idea
Idea 19509 The indexical aspect of contextual knowledge might be hidden, or it might be in what 'know' means [Schiffer,S]