Chén Yán 陳言 (zì Wúzé 無擇, fl. 1174, 南宋), Southern-Sòng physician of Qīngtián 青田 (modern Lìshuǐ, Zhèjiāng) — also known by the place-name epithet “Kuòcāng” 括蒼 (the older name for the region). Author of the foundational Sānyīn jíyī bìngzhèng fānglùn 三因極一病證方論 (KR3e0041, 18 juan, completed Chúnxī 1 = 1174) — the major Southern-Sòng medical-theoretical treatise that systematized the “Three Causes” (三因) doctrine of disease aetiology, drawing on the Jīnguì yàoluè’s fāyángfāyīn analysis. The Three Causes are: (1) Nèi yīn 內因 (internal: the seven emotions arising from the zàngfǔ and manifesting in the limbs); (2) Wài yīn 外因 (external: the six excesses arising from the channels and lodging in the zàngfǔ); (3) Bùnèiwài yīn 不內外因 (neither internal nor external: dietary, traumatic, and accidental causes). The work is the doctrinal turning-point at which Chinese medicine moved from formulary-based to aetiology-based clinical reasoning, anticipating and influencing the JīnYuán medical revolution. Yán Yònghé 嚴用和’s Jìshēng fāng 濟生方 (KR3e0044 = TBD) builds directly on Chén Yán’s framework. The catalog meta gives Chén’s fl. as 1500–1540 — clearly a transcriptional error; corrected here to fl. 1174 per the work’s own preface and the Sòng zhì.