Dasein

Heidegger's technical term — coined as a reiner Seinsausdruck (pure being-expression) — for the entity we ourselves each are, distinguished from all other entities by the fact that its own being is at issue for it. Dasein is not "human being," "consciousness," "subject," or "person"; it is the Seinsweise (mode of being) of the entity that lives in a pre-thematic Seinsverständnis (understanding of being) and whose own existence can be its own or not its own. "Diesem Seienden geht es in seinem Sein um dieses Sein selbst" — to this entity in its being, this being is at issue (Sein und Zeit § 4, H. 12).

Key Points

Definition by Existenz, not essentia. "Das »Wesen« des Daseins liegt in seiner Existenz" (SuZ § 9, H. 42). Dasein has no "what" prior to its "how"; its essence is its existence. The "characteristics" of Dasein are not properties of a present-at-hand entity but Existenzialien — modes of being-able-to-be. This is the central ontological wedge against the Cartesian / scholastic essentia precedes existentia tradition.
Jemeinigkeit (in-each-case-mineness). Dasein's being is je meines (in each case mine). This is not a phenomenological observation about reflexive consciousness but the Bedingung der Möglichkeit of the Eigentlichkeit / Uneigentlichkeit distinction. Address by personal pronoun ("ich bin", "du bist") is structurally required (SuZ § 9, H. 42).
Existenzial vs. existenziell. Dasein's ontic comportment toward its own existence is existenziell (e.g., the choice of a vocation). The ontological-structural analysis of what makes such comportment possible at all is existenzial. Existenzialien (existentials) are the structural categories of Dasein; Kategorien (categories) apply to non-Dasein entities (SuZ § 9, H. 44). This distinction (see existenzial-vs-kategorial for full treatment) is the silent organizing principle of Heidegger's entire analytic.
Dasein is not "human being." Heidegger explicitly refuses to use Mensch, Leben, Subjekt, Bewußtsein, Geist, Person — these names all carry uncriticized antique-ontological residue, treating Vorhandenheit (presence-at-hand) as the way Dasein is (SuZ § 10). The term Dasein is a reiner Seinsausdruck — it names a way of being, not an entity-with-properties.
Ontic-ontological priority. Dasein has a threefold priority over all other entities (SuZ § 4): (i) ontic — its being is at issue for it; (ii) ontological — it understands being (Seinsverständnis belongs to its mode of being); (iii) ontic-ontological — every regional ontology (of nature, life, history, etc.) presupposes the structure of the being-that-understands-being. Fundamentalontologie must therefore be sought in the existenziale Analytik des Daseins.
Dasein is its disclosedness. "Das Dasein ist seine Erschlossenheit" (SuZ § 28, H. 133). Dasein is the Lichtung — the clearing — in which entities can show up at all. The 1927 Lichtung-image is operative here, long before the post-Kehre essays on Lichtung-als-Aletheia. The wiki's lichtung page documents this development.

Details

Why "Dasein" rather than "human being"

The choice is methodologically loaded. Heidegger's argument (SuZ § 10): the traditional definition of the human as ζῷον λόγον ἔχον / animal rationale takes the Seinsart of the ζῷον in the sense of Vorhandensein und Vorkommen — being-present, occurring-among-other-entities — and the λόγος is added as a "higher endowment" whose own Seinsart remains as dark as that of the composite. The theological version of the definition ("faciamus hominem ad imaginem nostram") imports its Sein-determinations from antique ontology, and the modern res cogitans inherits both without interrogation. Each tradition thus already answers the question of Dasein's being — and answers it wrongly — before the analytic begins. The term Dasein is chosen to suspend these inherited answers.

Existenz, Existenzial, Existenziell

Three terminologically distinct registers:

Existenz — Dasein's mode of being, distinguished from Vorhandensein (which Heidegger reserves as the meaning of the medieval existentia). To "exist" in this technical sense applies only to Dasein; trees, hammers, and propositions do not exist, they are present-at-hand or ready-to-hand.
Existenzial — the ontological-structural register: the analysis of Existenzialität (the structural totality of existence). The book is an existenziale Analytik des Daseins.
Existenziell — the ontic register: the way each Dasein concretely lives out its existence (choosing this vocation rather than that, taking up this possibility rather than another). Existenzielle questions are settled only by existing, not by ontological analysis. "Die Frage der Existenz ist immer nur durch das Existieren selbst ins Reine zu bringen" (SuZ § 4, H. 12).

The existenzial analysis is not a substitute for existenzielle decision; it makes the structures of such decision intelligible without dictating its content. This is why SuZ refuses to deliver "philosophical anthropology" or normative ethics.

Dasein in its average everydayness

Heidegger insists that the analytic begin with durchschnittliche Alltäglichkeit — average everydayness — not because the everyday is "normal" but because it is the Seinsmodus in which Dasein is zunächst und zumeist (proximally and for the most part). "Was ontisch in der Weise der Durchschnittlichkeit ist, kann ontologisch sehr wohl in prägnanten Strukturen gefaßt werden" (SuZ § 9, H. 44). The everyday is also a positive phenomenon: even in Uneigentlichkeit the structure of Existenzialität is fully operative (Uneigentlichkeit "bedeutet aber nicht etwa ein 'weniger' Sein oder einen 'niedrigeren' Seinsgrad" — H. 43). Average everydayness is not the same as primitivity (§ 11, H. 50); a culturally highly developed Dasein can be in its average everydayness just as fully as a "primitive" one.

Gleichursprünglichkeit (Equiprimordiality) — the silent methodological principle

Heidegger's term Gleichursprünglichkeit ("equiprimordiality" / "co-originarity") does enormous methodological work across S&Z while never being argued for — it is a silent key of the Daseinsanalytik, used at strategic junctures to block reductive priority claims among the elements of Dasein's structure. Key attestations: § 12 (Dasein as "ein einheitliches Phänomen" — a unified phenomenon, no element reducible to another); § 28 ("Befindlichkeit und Verstehen sind gleichursprünglich bestimmt durch die Rede" — state-of-mind and understanding are equiprimordially determined through discourse); § 41 ("ursprünglicher Zusammenhang ... der die gesuchte Ganzheit des Strukturganzen ausmacht" — the original interconnection that makes up the sought-after wholeness of the structural totality); § 65 (the ekstatic-horizonal unity of temporality as the Sinn der Sorge). The most explicit methodological self-statement appears in § 28: "Das Phänomen der Gleichursprünglichkeit der konstitutiven Momente ist in der Ontologie oft mißachtet worden zufolge einer methodisch ungezügelten Tendenz zur Herkunftsnachweisung von allem und jedem aus einem einfachen »Urgrund«" — equiprimordiality has been ignored due to an unbridled methodological tendency to demonstrate everything's derivation from a single "primal ground."

The structural work of Gleichursprünglichkeit:

It blocks reductive priority claims. No element of Sorge (Befindlichkeit, Verstehen, Rede; or the threefold Existenz / Faktizität / Verfallen) is "more original" than another in a way that would let one derive the others. Each is constitutive on its own; the structural totality holds them together without grounding one in another.
It undergirds the anti-foundationalist phenomenological method. The fundamentum concussum reading of the Daseinsanalytik (Protokoll p. 40, see § "Fundamentum concussum" above) is operationally the same point as Gleichursprünglichkeit's methodological work: SuZ refuses the Cartesian-rationalist Urgrund-search. If Gleichursprünglichkeit is removed, S&Z's holistic-structural method collapses into a Cartesian search for a single Archimedean point.
It anchors the resistance to subject-predicate ontology. Subject-predicate logic privileges one term as bearer and others as predicates; Gleichursprünglichkeit names a structure where no term is the bearer. This is what makes the analytic of Dasein non-substantialist.
It is silently presupposed by the Existenzial/Kategorial distinction. The Existenzialien (Befindlichkeit, Verstehen, Rede, Sorge, etc.) are gleichursprünglich with one another; the Kategorien (Vorhandenheit's determinations) are not — they admit derivation. The asymmetry is structural.

The term is methodological-structural rather than thematic, which is why it does not warrant a dedicated concept page but is documented here as the silent organizing principle of the analytic. Cross-reference: the "single attestation" pattern in § 28's methodological self-statement is structurally similar to the Lichtungslosigkeit attestation in Nietzsche II — both are named once but operative throughout.

Eigentlich / Uneigentlich

The terms are terminologisch gewählt (terminologically chosen). They are not normative — uneigentlich does not mean "deficient" or "bad," and eigentlich does not mean "good." Both are existential modes available to Dasein on the basis of Jemeinigkeit: Dasein can be its possibilities as its own (eigentlich) or as those of the das Man (uneigentlich). Most Dasein lives most of the time uneigentlich; this is not a moral failing but the structural condition out of which any move toward eigentlich existence is possible. See also das-man (the existential structure of inauthentic self) and the discussion of Verfallen under sorge.

Dasein as Lichtung — the 1927 figure

§ 28 (H. 133) is one of the most consequential passages in S&Z: Dasein's Erschlossenheit (disclosedness) is figured as a Lichtung — Dasein is not a thing-illuminated-by-some-other-light but itself the clearing. "Es ist »erleuchtet«, besagt: an ihm selbst als In-der-Welt-sein gelichtet, nicht durch ein anderes Seiendes, sondern so, daß es selbst die Lichtung ist." The Lichtung-image is therefore not a post-Kehre invention but a 1927 figure that the later writings re-ground. The standard periodization (Lichtung = post-Kehre) flattens the trajectory; see lichtung §"From Dasein-Lichtung (1927) to Lichtung-of-Anwesenheit (post-Kehre)" for the full development.

The "Dasein" of post-Kehre Heidegger

After S&Z Heidegger increasingly suspects that the very framing of Dasein as the Befragtes of the Seinsfrage risks a transcendental-subjective misreading: the analytic of Dasein looks too much like a foundational anthropology. The post-Kehre writings re-position Dasein as "the locality of the truth of Being" — Being is the Gegend (province) / Spielraum (clearing) in which everything is deployed, and Dasein is its locus rather than its ground. See ontological-difference §"Heidegger's Development (as read by Merleau-Ponty)" for MP's three-stage reading of this development. The 1964 Handexemplar marginal at GA 14 p. 87 reframes the SuZ-Seinsfrage as "der verkürzte Titel für die Frage nach der Herkunft der ontologischen Differenz" — Dasein is the locus where the difference can be questioned, not its origin.

The 1927 Brief an Husserl: the Seinsart des Konstituierenden

The Brief an Husserl of 22 October 1927 (Anlage I) supplies the cardinal pre-SuZ-published statement of the Husserl-Heidegger philosophical disagreement on the Seinsart des Konstituierenden — written eight months after SuZ's publication and eighteen months before the 1929 rift:

"Damit aber ist nicht gesagt, das, was den Ort des Transzendentalen ausmacht, sei überhaupt nichts Seiendes — sondern es entspringt gerade das Problem: welches ist die Seinsart des Seienden, in dem sich »Welt« konstituiert? Das ist das zentrale Problem von »Sein und Zeit« — d. h. eine Fundamentalontologie des Daseins. Es gilt zu zeigen, daß die Seinsart des menschlichen Daseins total verschieden ist von der alles anderen Seienden und daß sie als diejenige, die sie ist, gerade in sich die Möglichkeit der transzendentalen Konstitution birgt." (GA 14 p. 130)

The cardinal Heidegger-Husserl-Übersetzung: the transcendental ego is not nichts-seiend (Husserl's tendency) but is the existing Dasein in its peculiar Seinsart. The Wundersame-Qualifizierung (single attestation in the published Heidegger): "die Existenzverfassung des Daseins ermöglicht die transzendentale Konstitution alles Positiven."

The 1962 Protokoll: Fundamentum concussum (the dropped Fundamentalontologie-title)

The Todtnauberg Protokoll (Session 1, GA 14 p. 40) supplies the cardinal late-Heidegger gloss on what dropping the Fundamentalontologie-title meant:

"Weil also das Fundament der Fundamentalontologie kein Fundament ist, auf dem aufgebaut werden könnte, kein fundamentum inconcussum, vielmehr ein fundamentum concussum ist, weil also die Wiederaufnahme der Daseinsanalytik schon mit zum Ansatz von »Sein und Zeit« gehört, das Wort ›Fundament‹ aber der Vorläufigkeit der Analytik widerspricht, deshalb wurde der Titel ›Fundamentalontologie‹ fallen gelassen."

The cardinal philological gloss: concussum (shaken) vs. inconcussum (Descartes' unshaken foundation of cogito ergo sum). The whole Vorläufigkeit of late-Heidegger thinking is grounded in the SuZ-Fundament being concussum from the start. The dropping of the Fundamentalontologie-title is structural, not stylistic: the Fundament was never a Fundament-on-which-to-build. The standard Fundamentalontologie → Ontologie → Regional Ontologies reading misreads SuZ as foundationalist; the Protokoll's concussum-formulation corrects this.

The Protokoll Session 1 also identifies the Grunderfahrung von SuZ as the Seinsvergessenheit: "Vergessenheit aber heißt hier im griechischen Sinne: Verborgenheit und Sichverbergen" (p. 37). The Verbergung des Seins gehört als deren Privation zur Lichtung des Seins; the Seinsvergessenheit gehört zum Wesen des Seins selbst. Therefore the SuZ task is not to abolish the Vergessenheit but to standing-into it and Entwachen (waking out) ins Ereignis. See seinsvergessenheit / enteignis.

The 1962 Brauch: Dasein replaced by Brauch-Verhältnis

The late-Heidegger Mensch-Bezug-zum-Sein is re-grounded outside the SuZ-Sorge-frame as Brauch. Marginal (11) at Zeit und Sein p. 23: "Vereignung: die Sterblichen sind in der Eignis eigens in ihr Eigenstes gerufen, insofern sie von der Eignis für diese selbst gebraucht bleiben."

The Beilage zum Vortrag (1973): "den Brauch, zur Eignis gehörend und das Da-sein mitnennend." The Brauch is to the Eignis belonging (Eignis-side) but names-with the Da-sein (Mensch-side). The Mensch is eingelassen (let-into) the Brauch; the Eignis braucht the Mensch for the Eignis selbst. See brauch for the developed concept.

The post-1962 Mensch-Bezug-zum-Sein is therefore neither SuZ-Sorge (Mensch-side existential) nor Husserlian transzendentale Konstitution (Bewußtsein-side activity) but Brauch-Verhältnis — the Wie of the Eignis's Vereignung of mortals. Da-sein in 1962 is what is mitgenannt by the Brauch; SuZ-Dasein is the prior approximation of what the late-Heidegger names Brauch-eingelassen.

Connections

is the locus classicus developed in heidegger-1927-sein-und-zeit — the foundational text.
is the structural totality articulated as sorge and temporalized as zeitlichkeit — see SuZ §§ 41, 65.
is brought into wholeness via sein-zum-tode — Dasein's Ganzsein is accessible only via Vorlaufen into death (SuZ §§ 46–53).
has as its everyday Wer das-man — not a sociological aggregate but an Existenzial (SuZ § 27).
is the Heideggerian counterpart to (but not synonymous with) being-in-and-toward-the-world — MP's être au monde takes a different path through the same structural region: corporeal-perceptual engagement rather than Zeug-handling and hermeneutic interpretation. The MP-Heidegger relation is archivally thinner than secondary literature typically asserts (see claims#mp-heidegger-reception-archivally-thin supported); MP's underlining of S&Z is concentrated in §§ 1–14 (Seinsfrage and Dasein-analytic foundations) and §§ 25–27 (Mitsein and das Man), without annotations.
requires ontological-difference — Dasein is the entity for which the difference between Sein and Seiendes is operative (and only operative). The 1964 essay reframes this: the Herkunft of the difference is the lichtung that grants both Sein and Seiendes their Anwesen zu und für einander.
enacts aletheia as Erschlossenheit — "Das Dasein ist seine Erschlossenheit" (SuZ § 28). Truth as uncovering operates in the disclosure-structure of Dasein.
is the operative ground of lichtung in the 1927 register — Dasein is the Lichtung (§ 28). The later writings re-ground the Lichtung outside the Dasein-frame.
is the silenced-but-stylistically-cited register in MP's late ontology — see heidegger-as-silenced-interlocutor and claims#mp-heidegger-reception-archivally-thin.
contrasts with Nietzsche's Übermensch — per heidegger-1961-nietzsche-i, the Übermensch is the metaphysical completion of the Cartesian subiectum whereas Dasein is the analytic move against that line. Heidegger's Vermenschlichung-critique of Nietzsche is structurally continuous with the SuZ refusal to start from "the human."
is genealogically prior to and developed beyond by ereignis — the post-Kehre Ereignis attempts to think the Herkunft of the Dasein/Sein relation that SuZ left as a closing aporia (§ 83, H. 437).

Open Questions

Is Dasein species-specific to the human? SuZ § 10 says biology is "in der Ontologie des Daseins fundiert" — biology is grounded in the ontology of Dasein. But § 10 also says: "Leben ist eine eigene Seinsart, aber wesenhaft nur zugänglich im Dasein" — life is its own way of being, but essentially accessible only in Dasein. Whether non-human animals can have a Daseinsanalytik-analogous mode of being is left open; Heidegger's 1929–30 Grundbegriffe der Metaphysik lecture-course (not in raw/) takes this up under "weltarm" (the animal as world-poor).
Does the Existenzial / Kategorial distinction depend on the very ontology it is supposed to make possible? A circularity-objection: to know that das Man is an Existenzial and not a Kategorial one needs already to have the analytic of Dasein. § 32 (hermeneutic circle) says this circle is benign; but whether it is benign is precisely what is at stake.
Why does Heidegger never argue against Husserl directly in S&Z? The dedication is in Verehrung und Freundschaft; the methodological remarks credit phenomenology to Husserl; yet the central move (analytic of Dasein) bypasses Husserl's constituting consciousness. The asymmetry deserves explicit interrogation.

Sources

heidegger-1927-sein-und-zeit — Einleitung §§ 1–8, Erster Abschnitt §§ 9–44, Zweiter Abschnitt §§ 45–83. The locus classicus. Key sites: § 4 (ontic-ontological priority of Dasein), § 9 (essence-is-existence, Jemeinigkeit, Existenzial/Kategorial), § 10 (refusal of "human being," critique of Lebensphilosophie/Personalismus), § 11 (Alltäglichkeit ≠ Primitivität), § 28 (Dasein als Lichtung), § 41 (Sorge as Dasein's structural totality), § 65 (Zeitlichkeit as ontological sense of Sorge).
heidegger-1927-brief-an-husserl — the cardinal pre-SuZ-published statement of the Seinsart des Konstituierenden-disagreement with Husserl. Anlage I (GA 14 p. 130) supplies the Existenzverfassung-ermöglicht-transzendentale-Konstitution-aller-Positivität-thesis with its Wundersame-Qualifizierung.
heidegger-1962-protokoll-zeit-und-sein — the cardinal late-Heidegger gloss on Dasein-Analytik: fundamentum concussum (p. 40) explaining the dropped Fundamentalontologie-title; the Grunderfahrung der SuZ as Seinsvergessenheit als Verborgenheit und Sichverbergen (p. 37); the Entwachen ins Ereignis (p. 38) as the proper Aufgabe; Brauch-Verhältnis (Brauch as Wie of late-Heidegger Mensch-Bezug-zum-Sein, replacing SuZ-Sorge as primary structure).
heidegger-1961-nietzsche-i — the Vermenschlichung-critique of Nietzsche extends the SuZ refusal to start from "the human."
heidegger-1964-end-of-philosophy — the 1964 Handexemplar marginalia at GA 14 p. 87 reframe the SuZ-Seinsfrage as "der verkürzte Titel für die Frage nach der Herkunft der ontologischen Differenz."
merleau-ponty-2022-possibility-of-philosophy — Course 1, Part II.B traces the three-stage development of Dasein from SuZ through On the Essence of Truth to the later writings; MP gives the most extensive published engagement.