<p>Cyberspace has emerged as a fourth fundamental domain of human existence, yet philosophy lacks an integrated framework for addressing the ontological, epistemological, and ethical transformations it produces. This paper develops such a framework through the concept of cyber, defined here as the existential condition in which human life becomes constitutively entangled with digital technologies such that the virtual and the real cease to function as separable categories. Distinguished from Wiener’s cybernetics (which concerns feedback and control) and Floridi’s infosphere (which foregrounds informational environments), cyber captures the deeper ontological entanglement that characterises the digital age. Employing the theoretical framework of cyberism, the paper serves as an integrated conceptual framework that advances three principal claims. First, digital entities such as digital twins possess genuine ontological standing by virtue of their causal efficacy, demanding that we expand our criteria for what counts as real beyond physical matter. Second, algorithmic mediation has precipitated a structural crisis in knowledge production and truth validation, threatening not only epistemological foundations but also democratic governance itself. Third, the technological reconfiguration of embodiment, identity, and agency necessitates a reconceptualisation of human subjectivity that draws on and extends the posthumanist insights of Haraway, Hayles, and Stiegler. The paper concludes by arguing that cyber ethics must move beyond reactive risk mitigation toward a participatory governance framework grounded in value-sensitive design and global deliberative consensus. These abstract commitments are operationalised through an extended case analysis of medical digital twins, which shows how ontological, epistemological, and ethical claims translate into specific design requirements and regulatory obligations.</p>