«كل كلام فهو إما خبر أو إنشاء»
Every utterance is either a report (khabar) or a nondeclarative utterance (inshāʾ).
A report makes an assertion concerning which truth or falsity can meaningfully be considered. Inshāʾ performs a communicative act, such as asking or calling, which is not itself characterized as true or false in that way.
“جَاءَ مُحَمَّدٌ” — “Muhammad came”: a report.
“يَا مُحَمَّدُ” — “O Muhammad!”: a call, hence inshāʾ.
The distinction rests not on length or emotional tone but on whether the utterance asserts something or performs a nonassertive speech act.