How did Martin Heidegger’s view of human existence challenge Cartesian philosophy?

Martin Heidegger’s philosophy fundamentally challenged the Cartesian conception of the human individual, which had long defined the subject as a "thinking thing" (res cogitans)—a mind or consciousness radically distinct from and cognitively isolated from the material world.123

Heidegger rejected this dualism, arguing that it created an artificial gap between the knower and the known that required unnecessary justification. Instead, he proposed the concept of Dasein, or "being-there," to describe human existence. His challenge to Cartesianism included:142

• Being-in-the-world: Heidegger posited that human existence is inherently "being-in-the-world," meaning individuals are always already caught up in, involved with, and committed to a sociocultural environment.245
• Rejection of the Thinking Subject: He discarded the idea of a mind that represents the world to itself through internal mental states. For Heidegger, practical, communal engagement with the world is ontologically more basic than theoretical or individualistic cognition.143
• Unitary Treatment: Rather than viewing humans as a compound of mind and body, Heidegger treated the individual as a whole, avoiding the sequestration of human functions into a "mysteriously conceived" mental part.13

By framing human reality this way, Heidegger rendered the traditional Cartesian subject-object problem superfluous.6