Full Idea
Acquaintance with sense data is supposed to be a form of non-propositional knowledge, but how can something be non-propositional and yet knowledge?
Clarification
'Non-propositional' means something something like 'not fully formulated with concepts'; 'sense data' are potential experiences
Gist of Idea
Sense data can't give us knowledge if they are non-propositional
Source
Michael Williams (Problems of Knowledge [2001], Ch. 8)
Book Reference
Williams,Michael: 'Problems of Knowledge' [OUP 2001], p.98