Identifying istiʾnāf requires more than saying “a question arose.” We must ask what the listener would naturally be questioning: the reason for the whole claim, a specific cause, its certainty, or an unclear part of its content.
Implicit questionRole of the next clause
Why did this happen?Give a cause for the event
Why this quality?Explain a particular feature
Is that really true?Confirm or substantiate
What does that mean?Clarify the earlier content
These are interpretive distinctions; the precise implicit question must be inferred from each passage's context.