Full Idea
When a sceptic brings up far-fetched possibilities and argues that we can't rule them out, he is not raising the standard for the word 'know'. He is showing it is tougher than we realise for a belief to qualify as normal knowledge at all.
Gist of Idea
Sceptics aren't changing the meaning of 'know', but claiming knowing is tougher than we think
Source
Kent Bach (The Emperor's New 'Knows' [2005], III)
Book Reference
'Contextualism in Philosophy', ed/tr. Preyer,G /Peter, G [OUP 2005], p.68
A Reaction
[Bach cites Richard Feldman for this idea] I think that what happens in the contextual account is that 'true', 'belief' and 'know' retain their standard meaning, and it is 'justified' which shifts. 'I am fully justified' can have VERY different meanings!