最後，一 Dasein 嘅「真實性」(authenticity) 問題離唔開Dasein嘅「歷史性」(historicallity)。 一方面，Dasein 係會死嘅 (mortal)，由生「拉」"stretched along" 到死，被氹落呢個世界，即係話，氹入佢嘅咁多「可能性」(possibilities)，呢啲可能性 Dasein 要負責做 (?assuming)。 另一方面， Dasein's access to this world and these possibilities is always via a history and a tradition—this is the question of "world historicality," and among its consequences is Heidegger's argument that Dasein's potential for authenticity lies in the possibility of choosing a "hero."
咁，再廣泛啲講， the outcome of the progression of Heidegger's argument is the thought that the being of Dasein is time. Nevertheless, Heidegger concludes his work with a set of enigmatic questions foreshadowing the necessity of a destruction (that is, a transformation) of the history of philosophy in relation to temporality—these were the questions to be taken up in the never completed continuation of his project:
The existential and ontological constitution of the totality of Dasein is grounded in temporality. Accordingly, a primordial mode of temporalizing of ecstatic temporality itself must make the ecstatic project of being in general possible. How is this mode of temporalizing of temporality to be interpreted? Is there a way leading from primordial time to the meaning of being? Does time itself reveal itself as the horizon of being?[11]
雖然海德格話自己喺《存在同埋時間》係用現象學嘅方法， 不過佢同胡塞爾現象學嘅關係就好複雜。The fact that Heidegger believes that ontology includes an irreducible hermeneutic (interpretative) aspect, for example, might be thought to run counter to Husserl's claim that phenomenological description is capable of a form of scientific positivity. On the other hand, however, several aspects of the approach and method of Being and Time can be seen more directly in relation to Husserl's work.
The central Husserlian concept of the directedness of all thought—intentionality—for example, while scarcely mentioned in Being and Time, has been identified by some with Heidegger's central notion of "Sorge" (Cura, care or concern). But for Heidegger, theoretical knowledge represents only one kind of intentional behaviour, and he asserts that it is grounded in more fundamental modes of behaviour and forms of practical engagement with the surrounding world. Whereas a theoretical understanding of things grasps them according to "presence," for example, this may conceal that our first experience of a being may be in terms of its being "ready-to-hand." Thus, for instance, when someone reaches for a tool such as a hammer, their understanding of what a hammer is is not determined by a theoretical understanding of its presence, but by the fact that it is something we need at the moment we wish to do hammering. Only a later understanding might come to contemplate a hammer as an object. There is thus a sense in which this kind of argument, although very different from Husserlian phenomenology, nevertheless resembles it, to the extent that what is involved is a kind of suspension of the everyday understanding of what it means to experience beings in the world.
This also necessitated a rejection of the Cartesian, disembodied Cogito: that is, an 'I' as a purely thinking object. 代之，海德格堅持，任何人類行為嘅分析都應由「我哋係喺世界入面」呢一事實開始 (not viewing it in an 'abstract' fashion): therefore the fundamental fact about human existence is our 'being-in-the-world'. Human beings, or Dasein (German" da—there/here; sein—being or its; dasein—existence), Heidegger insisted, are embodied beings who act in the world. He therefore rejected the 'subject-object' distinction assumed by most philosophers since Descartes and so rejected terms like Consciousness, ego, human being, Man, which are so laden with Cartesian dualism that, for his purposes, they are practically useless. Instead he uses the German portmanteau, Dasein.
Things are meaningful to us in terms of their use in certain contexts, which are defined by social, that is mainly practical, norms. However, all of these norms are radically contingent. Their contingency is revealed in the fundamental phenomenon of Angst, in which all norms fall away and beings show up as nothing in particular, in their essential meaninglessness. (Contrary to some existentialist interpretations of Heidegger, this does not mean that all existence is absurd; rather, it means that existence always has the potential for absurdity.) The experience of Angst reveals the essential finitude of Dasein.
The fact that beings can show up, either as meaningful in a context or as meaningless in the experience of Angst, depends on a prior phenomenon: that beings can show up at all. Heidegger calls the showing up of beings, truth, which he defines as unconcealment rather than correctness or correspondence. This "truth of beings", their self-revelation, involves a more fundamental kind of truth, the "disclosure of being in which the being of beings is unconcealed.", in Greek, aletheia.
It is this unconcealment of being that defines Dasein for Heidegger: Dasein is that being for whom being is an issue, that is, for whom being shows up as such. This is why Heidegger begins his inquiry into the meaning of being with an inquiry into the essence of Dasein; The unconcealment of being is an essentially temporal and historical phenomenon (hence the "time" in Being and Time); what we call past, present, and future correspond originarily to aspects of this unconcealment and not to three mutually exclusive regions of the homogeneous time that clocks measure (although clock-time is derivative from the originary time of unconcealment, as Heidegger attempts to show in the book's difficult final chapters).
The total understanding of being results from an explication of the implicit knowledge of being that inheres in Dasein. Philosophy thus becomes a form of interpretation; this is why Heidegger's technique in Being and Time is often referred to as hermeneutical phenomenology. Being and Time, being incomplete, contains Heidegger's statement of this project and his interpretation of Dasein and its temporal horizon, but does not contain the working out of the meaning of being as such on the basis of this interpretation. This ambitious task is taken up in a different way in his later works (see below) and had a profound influence on his student Hans-Georg Gadamer.
對海德格，哲學嘅衰嘢唔係 重未有外在於我地嘅世界（存在）嘅證明，而係從未有人去揾呢個證明。 At the same time his own project is hugely ambitious, in that he is interested not in the being of certain things, such as are studied in various (ontical) categories such as, biology, physics, psychology, and history, but in the question of being in general (the ontological question), of why or how there is something rather than nothing. Being in general is the most difficult because, like a smell that was always in our nose, it is almost always there, it is closest and for the most part there. Only in a state of anxiety (and not fear, which is fear of something in particular), where the whole world itself is pushed away, can we see something of this and get some authentic sight of it, before we again take up some activity and get lost in it.
At the same time that he tackles these soaring questions, he does so in a most practical way, by looking at how we encounter the world in a concrete and non-theoretical manner, how history and tradition affect us and are created by us, in effect how we live together and how our language and meaning is shaped through history by us. Though such a project might remind one of Hegel's pragmatism, Heidegger attempts to do this without resorting to any ideas of positing some overall goal of historical progress toward some Absolute, nor does he talk of the sublation (Aufhebung) of contradictions in some higher unity.
His view inverts the traditional priority of theory over practice. For him the theoretical view is artificial and comes from just looking at something without any involvement, such an experience is 'levelled off'. For Heidegger this attitude is given the moniker, "present-at-hand" and it is parasitic upon our more fundamental mode of interaction, called "ready-to-hand". Parasitic in the sense that in our history we must first have an attitude or mood toward the world before we can adopt a scientific or neutral attitude toward it. Such a re-evaluation of science allows him to say, for example, that the friend caught sight of across the road is in fact closer than the street upon which one walks, that the voice on a phone is closer than the handpiece, that the glasses pushed back on your head, can be, when not found, considered as remote and far away.
In addition to present-at-hand and ready-to-hand there is a third mode for Dasein, being-with, that is essential to Dasein. For example, a field that we may carefully walk around so as not to damage the crops or compact the soil, is ready-to-hand but shows itself also as belonging to someone and cared for by someone. We do not just add this person, "in thought," to the field we see because the farmer(s) already show themselves with the field through its improvements as the object of their care. Likewise, we may hear a scream, not as a noise or a sense-datum, but as someone in distress.
There is a dark side, however, to "being-with": referring to the "They", as in "they say it was carried out by terrorists." Heidegger notes that there is a tendency with assertions in general to simply pass it along without any context, as is the case with news or gossip.[12] Essentially, the idea of the "They" (Das Man) explores the existential notions of what is authentic or inauthentic.
用新嘅途徑去考察時間。 海德格話自從亞里士多德，大家都用差唔多同一種途徑去解譯時。 However, time in a primordial, that is a practical, sense, is always the time of something or time for something. We are involved in the world, in projects, and these swallow up time; for example, we open doors without explicitly giving time to it. The present emerges not out of itself but as the time we must act or not act, as a finite being we are always being-towards-death, being itself is an issue for us. Similarly, the past, through tradition, is transmitted to us or rejected by us, but we are thrown into a certain time; one cannot choose to be a genuine Samurai warrior in the twenty first century. The variety of ways time can be thought out, e.g., in Aristotle's simplistic past-present-future, and these others ways of thinking it out are referred to as temporality.
As part of his ontological project, Heidegger undertakes a reinterpretation of previous Western philosophy. He wants to explain why and how theoretical knowledge came to seem like the most fundamental relation to being. This explanation takes the form of a destructuring (Destruktion) of the philosophical tradition, an interpretive strategy that reveals the fundamental experience of being at the base of previous philosophies that had become entrenched and hidden within the theoretical attitude prevalent in the history of philosophy in its metaphysics of presence. Such "destruktion", is to be read not only in its negative sense but also in the positive sense of recovery. In Being and Time he briefly destructures the philosophy of Descartes though the second half of the book which was intended to be a Destruktion was never written; in later works he uses this approach to interpret the philosophies of Aristotle, Kant, Hegel, and Plato, among others. This technique exerted a profound influence on Derrida's deconstructive approach, although there are very important differences between the two methods.
