A common challenge in the study of classical civilizations is the confrontation with a complex notion for which there is no single rendering in modern discourse. The Greek 'logos' and 'mimesis' are famous examples. In the Arabic tradition 'bayān' is a case in point. Two decades ago Wolfhart Heinrichs remarked that “the notion of bayān ‘clarity’, ‘distinctness’ [is] a notion that is not clear and distinct at all and in dire need of a monograph.” While advances in the study of bayān have been made since the publication of von Grunebaum’s article in the Encyclopaedia of Islam, Heinrichs’ words still largely hold true today. Some legal aspects of the term have been studied by Lowry, Montgomery and Vishanoff, with a special focus on al-Shāfiʿī (d. 204/820). Skarżyńska-Bocheńska, Suleiman and Behzadi have concentrated on al-Jāḥiẓ (d. 255/868 or 9), interpreting the notion as a theory of communication akin to modern semiotics. Montgomery and Lowry see a link between al-Jāḥiẓ’s conception of the term and that of al-Shāfiʿī, but otherwise bayān has usually been studied in isolation. In this paper I offer a comprehensive investigation into the notion, starting from its lexical meaning(s) and early occurrences in poetry, the Qurʾān and ḥadīth. In addition to revisiting the texts of al-Shāfiʿī and al-Jāḥiẓ I look at the perspectives of fourth/tenth- and fifth/eleventh-century thinkers like Ibn Ḥazm, Ibn Wahb al-Kātib, Ibn Fāris, al-Rummānī, Abū Hilāl al-ʿAskarī and ʿAlī b. Khalaf al-Kātib. I identify four strands of meaning of bayān: the legal-hermeneutic, the philosophical, the philological and the scribal. A case will be made for a polygenetic origin of these meanings, stemming from the various lexical meanings of the word. While the legal-hermeneutic and philosophical meanings will be interpreted as epistemological mechanisms due to the semantic affinity between bayān and dalāla ‘signification’, the philological and scribal ones will be understood as instantiations of ‘eloquence’. Montgomery’s creative interpretation will be rejected on account of al-Jāḥiẓ’s work being assertoric in nature rather than deontic. Some light will be shed not only on early religious and literary thinking regarding the term, but also on the later appellation of the discipline called ʿilm al-bayān.