‘Dasein’ is a normal German word whose substantivization first occurred in the 18th century. You’ll find it in Kant and Hegel, for instance, where it means simply ‘existence’, i.e. that someTHING IS. Heidegger recasts the term entirely by shifting its signification from the existence of beings in general, and somewhats in particular, to mean the mode of being of human beings, i.e. of somewhos. In Heidegger’s phenomenology there is for the first time a well-worked-out, conceptual determination of whoness in distinction from the age-old concern of metaphysics with whatness, i.e. the being of ‘whats’, their ‘whatness’, ‘quidditas’ or ‘essence’. When Heidegger hyphenates Dasein as Da-sein or Da-Sein, there is a further twist, because the Da in Heidegger’s thinking is the temporal clearing itself within which all beings whatever (whats and whos) presence and absence. The clearing itself is the time-clearing of presencing itself, which is inconspicuous, hidden, whereas it is the presencing and absencing of ‘presents’, i.e. ‘occurrents’, 'what occurs', that Dasein (human being) sees and understands (hermeneutically) AS such. It’s very important not to think of Dasein as a sort of entity, but as the MODE of being, i.e. as the ways of presencing and absencing, and of revealing and concealing, of human beings AS somewhos. In one sense, Dasein can be thought of as existence or ex-sistence in the sense of standing-out, ex-posed to the three-dimensional temporal clearing of the Da.
It’s easy to get tangled making the distinctions between Dasein (human being, existence, quissity, whoness), Dass-sein (also Daßsein, existentia, thatness) and Was-sein (essentia, quidditas, Wesen, whatness). The English translation of Dasein as ‘there-being’ has the drawback that ‘da’ in German can just as easily mean ‘here’, and this signification is probably more appropriate when trying to think ‘Dasein’. In everyday German, “Ich bin da” means simply “I’m here”. So Dasein means ‘here in the Da’. As far as we know. only human beings are exposed to the Da; insofar, the translation of Dasein as ‘human being’ or ‘human existence’ is justified.
Since Sein und Zeit is the attempt to show that being means time, and this is never dropped by Heidegger (cf. e.g. the Zollikon Seminars), I think it is important to think of being itself (in distinction from the metaphysical concern with the Seiendheit des Seienden, i.e. the beingness of beings) as Anwesen, i.e. presence itself, and to think beings as Anwesendes, i.e. presents. And this is what Heidegger himself comes to in his interpretations of Parmenides. Since presence itself is threefold, comprising also two modes of absence (the refusal of presence and the withholding of presence), beings themselves must be thought as comprising both presents and absents (in the twofold sense). So in German one could say that beings (presents) comprise schon Abgewestes, Anwesendes and noch Anzuwesendes (i) that which has already absented itself, ii) that which is presently presenting itself, and iii) that which has yet to present itself). Crucial here is the three-dimensional temporal nature of the Da, i.e. of the time-clearing itself. 3D time is not linear as it is from Aristotle through to Kant and beyond (including in all modern science). There is no longer any washing-line of time on which occurrences are hung as simultaneous or successive; there is also no longer any time t# indexed one-dimensionally by a real, continuous number. Rather the three dimensions of presencing and absencing play freely into each other, impacting Dasein itself. This free play gives rise to a new meaning of ‘simultaneity’ in which the logical principle of non-contradiction (for which linear simultaneity is essential; cf. Met. Gamma 3, 1005b29f) loses its unquestioned validity.
(Originally posted on the An und für Sich blog.)
Further reading: Out of your mind? Parmenides' message.