First Among the Four Books, and Still Argued Over

Kafi was the first of what later tradition grouped together as the Four Books, joined over the following century and a half by Man La Yahduruhu al-Faqih, Tahdhib al-Ahkam and al-Istibsar. Its early completion and comprehensive scope made it the most frequently cited of the four in later legal and theological writing, and it remains the starting point for seminary study, the hawza, in Twelver Shia centers of learning today. That status has not made it uncontested. Twelver scholars have long disagreed over how many of Kafi's roughly sixteen thousand hadith can be treated as reliably authenticated, with estimates ranging from a small fraction judged fully sound (sahih) by the strictest chain-of-transmission standards to a much larger number accepted as usable for law or doctrine under looser criteria.

The disagreement tracks a broader split between the Akhbari school, which favors reading the Four Books more directly as reliable in their transmitted form, and the dominant Usuli school, which treats Kafi as raw material to be evaluated and reasoned over using the tools of jurisprudence (usul al-fiqh) rather than accepted wholesale. Both approaches keep Kafi at the center of the argument rather than settling it.