While previous research has characterised the Swedish author and educator Ellen Key's (1849–1926) concept of bildning as holistic, democratic, egalitarian, and as a process of individual self-formation, this study revisits these features and expands upon her well-known but less examined eugenicist ideas. The aim is to explore and contextualise Key's notions of bildning in relation to her eugenic visions of human development. This connection was made possible by Key's monistic worldview, which is analysed through her critique of dichotomous thinking. Four dichotomies are examined: body/soul, individual/society, nature/nurture, and reason/emotion. The analysis provides a detailed account of how Key's critique of these four dichotomies shaped her ideas on bildning and eugenics. The study concludes that Key's support for eugenics was not merely a peripheral interest reflecting the prevailing zeitgeist at the turn of the century but rather a central aspect of her conceptualisation of bildning and educational thought, which she saw as holding the promise of a new humanity.