A departure from the apparent form is not ungrammatical or obscure language. A speaker chooses a form that departs from the ordinary expectation because context and a specific benefit justify the choice.
The principal devices covered are treating a listener as informed, uninformed or denying in a special way; changing tense; using statements as prayers or imperatives for equivalence; shifting pronouns and explicit nouns; and iltifat, feigned ignorance, uslub al-hakim and taghlib.
Reliable analysis considers grammar, context, audience and intended effect together. The next discipline, ilm al-bayan, studies how simile, figurative expression and indirect indication convey meaning.