The purpose of this study is to examine the development of the elementary integrated curriculum, analyze its characteristics, and critically discuss its issues in relation to the conditions required for the existence of school subjects. The study investigates the nature and conditions of school subjects, reviews the evolution of the integrated subject from the 4th Korean national curriculum to the 2022 revision, and analyzes the current curriculum. The findings indicate that the integrated subject has shifted from additive integration based on original subjects to extra-disciplinary, theme-centered integration emphasizing students’ daily lives and experiences, and most recently, to an ontological approach focusing on learners’ lives and existence. However, these transitions have unfolded under the tension between efforts to establish subject identity and external pressures to meet disciplinary demands, leaving its status unstable. The ontological approach of the 2022 revision, while valuable in respecting students’ experiences, weakens the hierarchical and logical structure of content. The study argues for reconstructing a coherent knowledge system and reinforcing the bridging function across grade levels to ensure stability and educational value.