Analysis of the Use of Weak Transmitters in theIsnad of Kitāb al‑Kāfī

 Introduction
In the Shiʿi hadith tradition, attaining confidence in the attribution of a tradition to an infallible Imam is a foundational principle in the authentication of hadiths. While the common method among later scholars relies primarily on isnād-based reliability—evaluating each transmitter individually (especially in terms of justice and adherence to the Imami creed)—the approach of the early scholars (qudamāʾ) was broader and grounded in “wuthūq ṣudūrī". This means depending on multiple corroborating indications beyond mere chain analysis to achieve confidence in a tradition’s authenticity. Al‑Kulaynī, in the preface to his work al‑Kāfī, declares the traditions within it to be “authentic.” This statement has appeared problematic to later scholars, given that over half of the traditions in the book contain transmitters who are weak (ḍaʿīf), unknown (majhūl), or neglected (muhmal) in their chains. Hence, the present study is designed to address this key question: “By what criteria did al‑Kulaynī judge as authentic those traditions in al‑Kāfī that are transmitted through weak transmitters?” Understanding this issue is crucial both for reviving the early scholars’ methodology and for reassessing the most authoritative hadith source of the Shiʿa tradition.
Materials and Methods 
This research employs a library‑based analytical approach using a descriptive‑analytical method. The data include the text of al‑Kāfī itself, authoritative rijāl sources (such as Shaykh Ṭūsī’s Fihrist and Rijāl, al‑Najāshī’s Rijāl, and al‑Kashshī’s Rijāl), as well as prominent commentaries (for instance, al‑Majlisī’s Mirʾāt al‑ʿUqūl* and al‑Majlisī al‑Awwal’s Rawḍat al‑Muttaqīn), along with contemporary works in uṣūl al‑fiqh and hadith sciences (notably the writings of Āqā Ḍiyāʾ al‑ʿIrāqī, al‑Muḥaqqiq al‑Iṣfahānī, and Sarkhaʾī). The analytical process proceeds as follows: first, the weak transmitters appearing in al‑Kāfī’s chains are identified (based on rijāl judgments). Then, sample traditions with weak isnāds that al‑Kulaynī included are studied closely. Through reverse induction and cross‑referencing of sources, the indications (qarāʾin) al‑Kulaynī might have relied upon in accepting those traditions are extracted and categorized. For each category, supporting evidence from historical, legal, and hadith sources is provided, establishing the credibility of these criteria from both classical and modern scholarly perspectives. The analysis is further reinforced by engagement with contemporary juristic theories—such as the theory of trust in transmission (wuthūq fī al‑naql), authority of reports deemed issuing with certainty (ḥujjiyyat al‑khabar al‑mawthūq al‑ṣudūr), and the role of common juristic practice (shuhra fatwāʾiyya).
Results and Findings 
The study identifies nine key criteria on which al‑Kulaynī seems to have relied when accepting weak‑isnād traditions:
Reliance on the written works of early companions (text‑centered transmission): Over 70% of al‑Kāfī’s traditions are transmitted through teachers such as ʿAlī b. Ibrāhīm, Muḥammad b. Yaḥyā al‑ʿAṭṭār, and ʿAlī b. Muḥammad al‑Rāzī, who themselves either authored books or had transmission paths to well‑known written compilations by the aṣḥāb. An examination of these works (such as the books of Ibn Abī ʿUmayr, Yūnus b. ʿAbd al‑Raḥmān, and ʿAlī b. Mahzīyār) shows that al‑Kulaynī made use of weak transmitters mainly when they served as mere links through which a reliable written source was conveyed. 
Reliance on contextual indications to achieve certainty of issuance: For example, the tradition “The earth is never devoid of a divine proof” (lā tukhla‑wī al‑arḍ min ḥujja), which includes Sahl b. Ziyād (accused of ghuluw), was considered authentic by early scholars because of supporting indications—such as confirmation in other chains (from Aḥmad b. Muḥammad b. ʿĪsā and Muḥammad b. Abī ʿUmayr), reliance by the Companions of Consensus (aṣḥāb al‑ijmāʿ) like Yūnus, Ibn Maskān, and Abū Baṣīr, and internal consistency of content.
Fame of the tradition: In cases such as the tradition of the Covenant of Pre‑existence (ʿĀlam al‑dharr) or the ruling of impurity of a corpse before washing, the weakness in chain is offset by widespread juristic practice and frequent citation in multiple early sources (like al‑Barqī’s al‑Maḥāsin and al‑Ṣaffār’s Baṣāʾir al‑Darajāt).
Integrity of the transmitter at the time of transmission: For transmitters like ʿUthmān b. ʿĪsā and ʿAlī b. Abī Ḥamza, who later inclined toward the Wāqifī creed, al‑Kulaynī transmits traditions attributed to them that likely belong to their earlier trustworthy period—evidenced by the intermediary transmitters (e.g., Aḥmad b. Muḥammad b. ʿĪsā before discovering their deviation) and the absence of pejorative labels such as kalāb mamṭūra in the chains. 
Reliance on the famous written legacies of early companions: When a tradition existed in books such as those of ʿAlī b. Mahzīyār—whom al‑Najāshī described as “well‑known books” (kutub mashhūra)—even if al‑Kulaynīs connecting chain included a weak transmitter, the inherent credibility of these written sources and the trust of subsequent generations validated their inclusion. 
Presenting traditions to the Imams and their confirming: Numerous examples—such as the presentation of the Book of Sulaym b. Qays to Imām al‑Sajjād, or Yūnus’s Yawmun wa‑Layla to Imām al‑ʿAskarī, or the Imams al‑Jawād and al‑ʿAskarī confirming statements of Umm al‑Muʾminīn—demonstrate that the ʿarḍ (presentation and approval) of hadiths was among the strongest indications of authenticity. 
Istifāḍih Igmālī (semantic tawātur): In chapters such as "faḍl al-'ilm" or " 'ilm Imamas", the recurrence of the same concept in several traditions with varying weaknesses establishes sufficient confidence in the reliability of the content. 
Multiple weak Isnads supporting a single text: In cases such as “Seeking knowledge is an obligation” (ṭalab al‑ʿilm farīḍa) or “The Imams are the tree of prophethood”, the convergence of several weak isnāds toward a single text strengthens the tradition under the rule of “improbability of collusion in falsehood”. 
Reinforcement of a weak tradition by a ṣaḥīḥ one: Examples in chapters like " 'arḍ al-a'māl" or "al-a'immah shagaratu al-nnabawwah" show that al‑Kulaynī deliberately juxtaposed weak‑isnād traditions with sound ones to preserve multiplicity of reporting while compensating the chain’s deficiency through content reinforcement. 
Conclusion 
Based on these findings, al‑Kulaynī, as he claimed in the preface of al‑Kāfī, did not rely solely on the criterion of transmitters’ justice and adherence to the Imami doctrine. Rather, he followed a broader approach founded on certainty of issuance (wuthūq ṣudūrī). His criteria can be classified at two levels: 1. Textual criteria — such as consistency of meaning with established Shiʿi doctrine and textual fame; and 2. Isnad criteria — such as reliance on written sources, confirmation by an Imam, multiplicity of transmission paths, and contextual indications concerning the transmitter’s time and condition. These findings have dual significance: first, they provide a foundation for a more precise reevaluation of al‑Kāfī and the other four major Shiʿi hadith collections in light of early methodology; and second, they demonstrate that the ancient method is not only defensible but, as affirmed by certain modern scholars (such as Āqā Ḍiyāʾ al‑ʿIrāqī and al‑Muḥaqqiq al‑Iṣfahānī), holds a solid position within the Usuli system. This research also represents an innovation as the first comprehensive study in this field.