This study delves into the semantic evolution of the Korean lexeme seysang . Despite its rich functional development, seysang has received limited attention in grammaticalization research. This study addresses this gap by exploring its extended meanings and functional shifts in Korean. It aims to trace the transformation of seysang from a historical noun to its role as a contemporary discourse marker (DM) which conveys a range of pragmatic meanings, marking the speaker’s emotions and stances. Using historical and contemporary corpora, including data spanning from the 15th century to modern media, this paper qualitatively analyzes the grammaticalization process of seysang while quantitatively examining the discourse functions of seysangey . The analysis particularly focuses on seysangey ’s positional flexibility within Left Periphery (LP), Right Periphery (RP), and stand-alone positions, and its preference in positive, negative, and neutral contexts. This study further investigates whether seysangey ’s LP and RP functions align with previous research, which associates LP with subjectification and RP with intersubjectification. The analyses indicate that seysangey exhibits both subjectification and intersubjectification across LP, RP, and stand-alone positions. Findings reveal that seysang has expanded to signify broader social spaces, from birth-to-death spans and societal environments beyond enclosed communities to symbolic meanings of people’s hearts and the earthly realm. It also functions adverbially as ‘very’ (degree modifier) and ‘at all’ (negative polarity item). In Contemporary Korean, seysangey operates as a flexible DM marking subjectivity, intersubjectivity, and speaker stance, providing insight into the complexities of language evolution and external influences shaping the Korean lexicon and grammar.