1. Chronology and contact: Were narrator and teacher contemporaries? Is an actual encounter established, or only a plausible possibility?
2. Mode of acquisition: Was the report heard, read aloud, authorized, handed over, written to the pupil, found, or received by another method?
3. Authorization and identity: If a book changed hands or was discovered, was narration explicitly authorized? Were the work and recipient specified?
4. Transmission formula: Does the isnād wording truthfully represent the established event, or does it assert more than is known?
Example: With “ʿan fulān,” investigate chronology, tadlīs, and contact. With “ajāzanī,” investigate permission and its scope. With “wajadtu bi-khaṭṭi fulān,” verify authorship and avoid implying personal hearing.
A transmission formula makes a claim about history. It is not merely an ornament to the chain; it must be assessed alongside, but separately from, the other conditions of hadith soundness.