How does Heidegger’s Dasein differ from Descartes’s thinking subject?

In Martin Heidegger’s philosophy, the concept of Dasein represents a fundamental departure from the René Descartes-inspired view of the human individual as a "thinking subject."1

The primary differences include:

• Being-in-the-world vs. Isolated Subject: Descartes conceived of the individual as a mind or soul radically distinct from the material world, leading to the problem of being "cognitively isolated" from it. Heidegger rejected this, defining the human individual as Dasein—or "being-in-the-world"—which implies that we are inherently situated within the world rather than separated from it.1
• Unitary Existence vs. Mind-Body Dualism: Descartes’s model relies on mind-body dualism, sequestering human functions into a "mysteriously conceived" mind or soul. Heidegger’s Dasein is a unitary concept of the human individual as a whole, avoiding the need to mediate between internal mental states and an external world.12
• Disclosive Function: Rather than a mind that merely represents the world to itself, Dasein is the "locus" of Being. It functions by "uncovering" or disclosing entities, allowing them to show themselves as what they are.1

Ultimately, Heidegger dropped the Cartesian notion of consciousness as internal awareness, replacing it with the active, temporal character of Dasein.1