How does Heidegger describe being-in-the-world?

In his seminal work Being and Time, Martin Heidegger rejects the Cartesian view of the human individual as a "thinking subject" isolated from the world. Instead, he defines the human individual as Dasein—literally "being-there"—which is fundamentally characterized by "being-in-the-world".123

Heidegger describes being-in-the-world as a state of already being caught up in, involved with, or committed to other individuals and things. This concept replaces the traditional notion of consciousness as an internal mental state, suggesting that human existence is not a mind sealed off from reality but a "locus" where entities disclose themselves.213

Key aspects of this description include:
* Unitary Existence: Dasein is a whole, not a compound of mind and body, meaning human functions are not sequestered in a "mental" compartment.13
* Practical Engagement: Our practical involvements and commitments are ontologically more basic than abstract thinking.2
* Temporality: Dasein is "ecstatically" oriented toward its own possibilities, always "out ahead of itself," rather than existing as a passive object.23

Ultimately, being-in-the-world signifies that engagement with the world is the very essence of human existence.2