Among the various ideas debated in classical Islamic legal theory (uṣūl al-fiqh), the concept of bayān was considered to be very controversial. Due to the ambiguity of the term bayān, discussions about its numerous definitions and applications fill many chapters in the legal theoretical texts of classical Islamic scholars. In early works on legal theory, bayān was taken to denote hermeneutical relationships between religious sources of Islamic legal rulings, i.e. the way in which Qurʾān and Sunna interact with each other in the course of deriving legal rulings from them. However, the concept of bayān developed to represent a hermeneutical hierarchy in which revelational language was classified with regard to its level of clarity. The technical terms used in this framework became the subject of detailed discussions that attempted to classify a revelational expression as being clear or unclear, as being unambiguous or polysemic, as having a plain meaning or being in need of explanation. Scholars in the field debated such issues in their quest for a systematic and internally consistent vision of Islamic law: How are such labels as ẓāhir, mujmal, mubayyan, or muʾawwal to be defined, what is their place in the hierarchy of clarity, and what does such a label mean for the legal ruling? In his work on Islamic legal theory, entitled al-Maḥṣūl fī ʿilm al-uṣūl, the polymath Fakhr al-Dīn al-Rāzī (d. 1210) gives an extensive answer to these questions, systematizing this hermeneutical vocabulary in the context of discussions on bayān by drawing on the works of his predecessors in the fields of legal theory (e.g. Abū Bakr al-Bāqillānī), rhetoric (ʿAbd al-Qāhir al-Jurjānī), and logic (Ibn Sīnā). In this systematization, he brings together the different terminologies that denote several states of clarity, unclarity, and polysemy in these disciplines, thereby merging several labeling systems into one. This paper aims to present Fakhr al-Dīn al-Rāzī’s innovative new systematization of hermeneutical vocabulary, analyze the different strata and disciplines on which this systematization is built, and explore the impact it had on subsequent works within the context of bayān.