ولكل كلمة مع صاحبتها مقام
Every word has a rhetorical station in relation to the word that accompanies it.
Contextual fitness operates not only at the level of an entire sentence. The combination of words and particles affects the meaning and the occasion for which an expression is suited.
The book develops this through conditional particles: in and idha can both accompany a verb, but they are not interchangeable in all rhetorical circumstances. The combinatory context helps determine the fitting choice.