Traditionally divided into:
Recorded in Hadith [reports]: Huge literature on many topics, not all of it reliable. Attempts to collect the reliable traditions in authoritative collections by Al-Bukhari, Muslim, etc. (9th century).
Includes traditions about what the Prophet
Narrators were evaluated for their trustworthiness.
Afterwards the hadiths were judged according to their content (e.g., whether they conformed to the Qur'an, or were logically plausible.
Hadith traditions were classified as
"Truly my umma will never agree together on an error."Originally applied to consensus of the community as a whole, later limited to the specialists (`Ulama).
Others include
The latter are no longer in force among Sunnis:
"The gates of ijtihad are closed."
However it is still practiced by the Shi`ites, for whom the authority of the Imam replaces Ijma' and Qiyas.
(Attempts to reopen "gates of Ijtihad" to modernize the religion).
Four main schools of interpretation, usually determined by country.
Shi'ites have their own schools, notably the Ja'fari.