The traditional classes are tablīgh, ighrāq and ghulūw. They are not merely “strong, stronger, strongest.” The decisive distinction is the claim's status under rational possibility and ordinary experience.
KindRational possibilityCustomary possibility
TablīghPossiblePossible
IghrāqPossibleOutside ordinary possibility
GhulūwImpossibleImpossible
Customary possibility is not limited to what every reader has personally witnessed. It concerns what ordinary causal experience can admit.