Full Idea
Sentences are implicitly contradictory, because they can be used differently in different contexts (most obviously in 'I am ill').
Gist of Idea
Sentences are contradictory, as they have opposite meanings in some contexts
Source
Jacques Derrida (works [1990]), quoted by Barry Stocker - Derrida on Deconstruction
Book Reference
Stocker,Barry: 'Derrida on Deconstruction' [Routledge 2006], p.68