The term Safah (foolishness) in Islamic texts—particularly in the Holy Qur’an and the narrations of Imam Ali (as)—represents a multilayered and interdisciplinary concept that acquires diverse meanings across linguistic, jurisprudential, and social contexts. This study adopts a semantic–comparative analytical approach to elucidate the semantic evolution and functional dimensions of safah in the Qur’an and Nahj al-Balaghah, as well as to examine its reflection in Imami jurisprudence and contemporary legal systems. The research employs a descriptive–analytical and comparative method, drawing data from library sources categorized into three domains: Qur’anic, narrative, and jurisprudential. Findings indicate that safah in the Qur’an is variously used to denote ignorance and frivolity, legal incapacity (hajr), or intellectual and moral imprudence. In the thought of Imam Ali (as), the concept transcends linguistic boundaries and extends into the realms of social behavior and rational action—portraying safah in Nahj al-Balaghah as a manifestation of deviation in reasoning and a lack of social responsibility. Within Imami jurisprudence, safah is defined as “incapacity in financial and legal dispositions,” a concept reflected in Article 1207 of the Iranian Civil Code. The innovation of this research lies in its integration of linguistic, jurisprudential, and sociological analyses of safah, which together illuminate its position within the Islamic epistemological framework and contribute to a reinterpretation of the relationship between religious rationality and social order. The results of this analysis can inform the formulation of social and legal policies concerning irrational behaviors and the lack of individual legal capacity in Islamic societies.