Full Idea
Dispositional facts are facts about what we will do, not about what we ought to do, and as such cannot capture the normativity of meaning.
Clarification
'Normativity' concerns creating and following rules
Gist of Idea
Dispositions say what we will do, not what we ought to do, so can't explain normativity
Source
Alexander Miller (Philosophy of Language [1998], 6.2)
Book Reference
Miller,Alexander: 'Philosophy of Language' [UCL Press 1998], p.181
A Reaction
Miller is discussing language, but this raises a nice question for all behaviourist accounts of mental events. Perhaps there is a disposition to behave in a guilty way if you do something you think you shouldn't do. (Er, isn't 'guilt' a mental event?)