The term he will use to designate the being of the entity he calls Dasein is existence. The important thing about existence, in contrast to other modes of being, is the understanding of being. To say that Dasein exists is to say that Dasein is in such a way that it understands being — its own being but also the being of things other than itself to which, as Heidegger will put it, it comports itself.
The basic structures of the being of Dasein he will call existentials. These are contrasted with categories, which refer to the basic structures of the beingof entities other than Dasein. The most basic of the structures of the being of Dasein is what he will call being-in-the-world. Dasein is in the world not in the sense of one thing being spatially contained in another thing but rather in the sense of being engaged with things. Dasein is not a subject for which the world is an object over against it. It is possible for Dasein simply to behold things, but such mere beholding is only possible as a modification of engaged having-to-do-with things. The things with which are engaged are in a broad sense used or employed. Such entities are what he will call ‘equipment’ (Zeug). He speaks of such entities as being ‘ready-to-hand’ or ‘available’ (zuhanden) and of their mode of being as ‘readiness-to-hand’ or ‘availableness’ (Zuhandenheit or Zuhandensein). This is contrasted with the being of things and their properties which simply occur, which he calls presence-at-hand (Vorhandenheit or Vorhandensein). Dasein is in the world in the sense of being engaged with [5] things, but what Heidegger means by world is not itself an entity, not even the totality of entities (of what is), but the web of significance which makes it possible for entities to show themselves or be encountered. World has to do, not so much with what is, but with the openness of what is. He will speak of different modes of comportment to entities. Understanding of world is not itself a mode of comportment to entities but rather what makes comportment to entities possible.
The being of Dasein is always someone’s being, or as Heidegger puts it, is always mine. This character of being a self, this selfness, is not to be understood in terms of a persisting non-material something which through its persistence and self-sameness unites the multiplicity of my mental states and makes them my mental states. The sense in which Dasein is a self is one which involves the possibility of choosing ways of existing. But that the being of Dasein is always mine does not mean that Dasein is something essentially private and isolated. The being of Dasein is being-in-the-world, but the world is not my private possession but a shared world. Being-in-the-world is being-with-others-in-the-world. Relationship to others is not just a contingent fact about Dasein, the fact that I am not the only one of my kind. Being alone is a possibility but it is only possible on the basis of being-with. Being- with does not depend on inference from bodily appearance and behaviour. But nor does it depend on something non-inferential like empathy. Empathy is not the bridge between one private subject and another private subject but is itself made possible by being-with.
Heidegger will speak of the being of Dasein being disclosed in Dasein (though he will also make it clear that this is inseparable from the disclosing of the being of entities other than Dasein and of being as such). The ‘Da’ (or ‘there’) in Dasein refers to such disclosedness rather than to spatial location.
[6] There are two basic modes of disclosedness — affectedness (Befindlichkeit) or mood (Stimmung) and understanding (Verstehen). In the first of these Dasein is disclosed in its thrownness (Geworfenheit), its sheer thatness. In the second it is disclosed in its possibility, its ability to be. In understanding how to be Dasein is projecting itself onto possibilities of existence. So he will say that the being of Dasein is thrown projection.Dasein is thrown into the world (is always already in the world) and is always ‘ahead of itself in the sense of projecting itself onto possibilities. It is also engaged with entities within the world (given Heidegger’s terminology chairs and tables, sticks and stones are within the world but not in the world. Only Dasein is in the world). These three basic features of existence — thrownness, projection and engagement, or what he will call ‘concern’ (Besorgen) — in their essential interconnection are what he will call ‘care’ (Sorge). Heidegger’s answer to the question ‘What is the being of Dasein?’ is the being of Dasein is care — in this sense of ‘care’.