What is tafsir, and how did al-Tabari and Ibn Kathir read the Quran?

Muslims have long written commentaries on the Quran. A commentary is called a tafsir, "explanation", and its author is a mufassir. By tradition, interpreting the Quran began with Muhammad and passed to his companions. The earliest commentary that survives was written by Muqatil ibn Sulayman in the middle of the 8th century, and in its formative age tafsir was a special branch of hadith before becoming a discipline of its own.

Broadly, there are two styles. Tafsir bi-al-ma'thur means "received tafsir": explanation that comes from Muhammad and his companions. Tafsir bi-al-ra'y is "tafsir by opinion", reached through the commentator's own reflection and independent reasoning.

Two classic commentators, both counted as examples of the received approach, show it at work in different ways. Al-Tabari's Jami' al-bayan is the earliest major running commentary on the Quran to survive in its original form. It is famous for its comprehensiveness and for citing many, often conflicting, sources, with the chain of narrators for each report. A story says he once offered his students 30,000 pages, they protested that no life would be long enough, and he cut it to 3,000. Western scholars thought the work lost until the 19th century. Ibn Kathir, who was born in what is now Syria and lived about 1300 to 1373, was the first to try out his teacher Ibn Taymiyya's stricter method: explain the Quran only by the Quran or the sunnah. His commentary has few personal remarks and avoids Isra'iliyyat, stories from Jewish, Christian or other non-Muslim backgrounds. His work was marginal in his own era and became very popular in modern times.