This is a study of Mullā Ṣadrā's arguments for the necessity of the imamate based on a chapter from his commentary on al-Uṣūl al-kāfī, one of the earliest canonical collections of the Shīʿī traditions (ḥadīth). After an overview and brief literature review of the subject, the paper shows Mullā Ṣadrā's use of philosophical teachings to prove the most pivotal doctrine of his Shīʿī faith. It summarizes the philosopher's arguments under the two categories of knowledge and existence. At the level of knowledge, the unrivaled access of the Imam/ḥujja to true knowledge after the Prophet makes him the only one who can reach the depth of the Qurʾan, hence the necessity of his existence in every age. As for the existential aspect of the imamate, Mullā Ṣadrā argues that there are intermediaries through whose existence the hierarchical ladder of creation unfolds, and he considers the Imams to be such intermediaries without whom nothing would exist.