Being and Time (Sein und Zeit, 1927) opens by reviving the oldest question in philosophy — the question of Being (Seinsfrage). We say a rock is, a number is, a person is. But what does that little word mean? Heidegger argues the tradition forgot to ask, mistaking beings (things that are) for Being itself.
His method is phenomenology — describing how things actually show up in lived experience, before theory tidies them away. And his strategy is indirect: to ask about Being, start with the one being who already understands Being and cares that it is — us. That's why the book becomes an analysis of human existence first.
Question of Being → analyze Dasein → uncover its structure as care → reveal its ground in time.
The book was never finished. The planned second half never appeared — fitting for a question Heidegger thought could only be reopened, not closed.
Hence the title: the meaning of Being turns out to be Time. The rest follows the route inward.
Heidegger calls the human being Dasein — literally "being-there." Not a mind looking out at reality, but an existence already woven into a situation, always somewhere, always involved.
Dasein is unique: it's the being for whom its own being is a question. A stone simply is; you are always interpreting, taking a stand on, mattering to yourself. Existence isn't a fixed essence you possess — it's something you're always carrying out.
The hyphens matter. "Being-in-the-world" is one phenomenon, not three parts glued together. You can't pry the self loose from its world without destroying both.
The old picture: a thinking subject locked inside, peering out at objects "out there," forever bridging a gap. Heidegger rejects it. There is no gap to cross — Dasein is already outside, already amongst things.
How do we usually meet things? Not by staring at them, but by using them. When you hammer well, the hammer vanishes into the task — Heidegger calls this ready-to-hand (zuhanden).
Only when it breaks does it surface as a mere thing with properties — present-at-hand (vorhanden). Detached observation is the exception, not the rule.
No tool is an island. A hammer refers to nails, to wood, to a workshop, to the shelter being built — and finally back to Dasein's own projects. The "world" is this whole web of references and purposes.
Meaning runs along these arrows. A thing only is what it is by its place in this totality of involvements.
You did not choose your birth, era, language, or body. Dasein is thrown into a world it didn't make. Yet it's never inert — it's always pressing into possibilities, taking a stance on its own existence.
Always already situated — a past, a culture, a body we were handed, not picked.
The unifying structure: to be Dasein is to have your own being be an issue for you.
Mostly we don't live as ourselves. We do what "one" does, want what "one" wants — Heidegger calls this anonymous public self das Man, "the they." It's comfortable and inescapable, but it lets us drift through life on borrowed answers. This is inauthenticity: not a sin, just falling-in with everyone.
What breaks the spell is being-toward-death. Death is the one possibility no one can take over for you — your ownmost, non-relational, certain end. Facing it (in anxiety, not mere fear) wrenches you out of the "they" and returns your life as yours to own. That's authenticity.
And here the two halves of the title finally meet. Care — the structure of Dasein — turns out to be temporal through and through. To exist is to stretch across three "ecstases" of time at once:
The future leads: Dasein is always ahead of itself, projecting toward possibilities — ultimately toward death. That's why, for Heidegger, the meaning of Being is Time.
The self and world belong together in the single entity, the Dasein. — after Heidegger, on dissolving the subject–object split