The doctrine of prophetic infallibility (ʿiṣma) constitutes one of the foundational cornerstones of Islamic theology within the discourse of general prophethood (al-nubuwwa al-ʿāmma),underpinning the epistemic stability of religion, the cognitive veracity of divine revelation, and the normative authority of prophetic exemplarity. Imam Fakhr al-Dīn al-Rāzī, the preeminent Ashʿarite theologian and exegete, conceptualizes the operative mechanism of infallibility through the divine instantiation of deterministic motive (khalq al-dāʿī) coupled with the negation of autonomous human agency (istiṭāʿa).This study offers a critical investigation into the theoretical foundations, scope, arguments, and theological ramifications of al-Rāzī’s “theory of motive,” systematically bifurcating the inquiry into two distinct analytical tiers: an immanent (intra-discursive)critique grounded in al-Rāzī’s own Ashʿarite ontological and causal commitments, and a transcendent (extra-discursive)critique formulated upon the rationalist axioms of ʿAdliyya theology. Employing a descriptive-analytical methodology anchored in primary classical theological and exegetical literature, the findings reveal that while al-Rāzī strictly upholds absolute infallibility in the reception and conveyance of divine revelation and the promulgation of legal ordinances (aḥkām)—corroborating it with both rational and scriptural proofs—he circumscribes its scope in the practical conduct and life of the prophets by conceding the permissibility of pre-prophetic sins and post-prophetic inadvertent minor infractions (al-ṣaghāʾir al-sahwiyya). The immanent critique demonstrates that grounding the mechanism of infallibility in a deterministic theory of motive precipitates an irreconcilable structural paradox with al-Rāzī’s own cardinal premise regarding the voluntary superiority (afḍaliyya)of prophets over angels, a status traditionally predicated upon deliberate moral struggle (mujāhada) against the concupiscent and irascible faculties—a struggle rendered conceptually vacuous under motivational determinism. Concurrently, from a transcendent critique standpoint, this conceptualization drives the normative exemplarity of the prophets into an epistemic impasse, while temporally confining infallibility strictly to the post-call period fundamentally compromises the teleology of the prophetic mission (naqḍ al-gharaḍ) and induces psychological estrangement (tanaffur al-qulūb).