The account of being-in-the-world is significant in the part it played in the Heideggerian break from the project of Edmund Husserl and the development of phenomenology thereafter. The break itself is also a vital underpinning of existentialism, as Terry Eagleton notes “To move from Husserl to Heidegger is to move from the terrain of pure intellect to a philosophy which meditates on what it feels like to be alive.” This particular form of phenomenology might be referred to as hermeneutical in contrast to the transcendental phenomenology which Husserl promulgated. In fact it has been said that Heidegger seized on the conception of phenomenology for his own ends, to the extent that the definition of “phenomenology” came to mean almost the exact opposite of the Husserlian proposal. Rather than emptying out the intentional contents of our belief system, to uncover datum, we let the things which are shared but cannot be articulated to reveal themselves.
If we accept the notion of intentionality put forth by Husserl then we take consciousness as always consciousness of something. So there is an internal relation between the act of thinking and the object of thought, a mutual dependence. Thought points towards some object. The mind does not passively acknowledge the world, it actively ‘intends’ the world. This is where the idealism of Husserl is quite overt, he thought it was absurd to see the world as external to thought and experience. Husserl goes on to claim that the way to establish certainty is to do away with – to ‘bracket’ – everything which is beyond our consciousness. All realities must be treated as appearances in our minds, pure phenomena and this is the universal data from which we can proceed. It is universal in the sense that it has universal implications, so that the examination of what we perceive, through the phenomenological reduction, is a way to get at the universal essence of the things we perceive as well as the act of perceiving.
Martin Heidegger breaks with Husserlian phenomenology with the ‘transcendent subject’ as its beginning. This is rejected as a suitable beginning by Heidegger and with it he rejected the ‘bracketing’ method. For Heidegger the subject-object distinction is an unwelcome bi-product of Cartesianism, for it is not only artificial but unsustainable. We can refer to the relation between the self and the world, insofar as we must refer to that relation as a distinction in order to move beyond it. Being-in-the-world captures the involved nature of the human subject, it is not dominant as the Enlightenment thinkers had thought, but is engaged in dialogue with the world. The point is to return to a pre-Socratic position, before the dualist distinction and wherein both of which can plausibly be encompassed by Being. We inhabit a reality which we are incapable of subjecting to objectification, for we are as much constituted by reality as we constitute it. So we should listen rather than speak in this dialogue. Whether or not we can charge Heidegger with idealism over this is complicated.
We could run with the view that Heidegger is an extreme idealist going by what he tells us about Reality, which is composite of: the Being of beings and Being as the pure presence-at-hand of Things. Robert Solomon argues that the dichotomy of idealism versus realism is insufficient for the bold moves Heidegger made. The problem is with the labels themselves as Heidegger should not be seen as a philosophical opponent of realism. By realism here we designate the view that there is a reality which can be known, which Heidegger does not deny, whereas idealism is the view that we can only know the products of our own minds. This is the reason that it has often been said that Edmund Husserl is an idealist.
There is a sense in which the world refers to being-in-the-world for Heidegger, at the same time being-in-the-world refers to Dasein and care is its primordial structural foundation. For Heidegger it is not that the concept being-in-the-world can be simply sliced into easily digestible components. Heidegger goes as far as to claim that care encapsulates Dasein in its’ entirety. It is not meant in the usual sense of caring for something, even indifference to something counts as a part of care. Dasein must deal with the world as it is being-in-the-world, without the world there is no subject and without the subject there is no world. Sartre would say Dasein is “condemned to be free”, but it is important to add that it is ‘condemned’ as it is ‘thrown’ into a world which has already set the ready-at-hand equipment and the paths we can take. For this reason Heidegger is closer to Nietzsche than Sartre on the question of free-will. We are not totally free individuals in a leveled world from which we are only floating through, but we are embedded and engaged without a choice in the matter. When we talk about being-in-the-world we are talking about a future-directed agent in its aware of possibilities in the situations it is involved in. It can encounter objects when lost in activities and this may be the way that we ‘flee from being’ which we might think of as ‘bad faith’ since Sartre.
At this point we should go back to the Heideggerian break, as it is important to stress, as Hubert Dreyfus does, that the break with transcendental phenomenology to establish hermeneutical phenomenology is not simply attributing a primary status to practical activity. Rather it is Heidegger’s position that the relation between a self-sufficient mind and an external world cannot be understood as detached contemplation or practical activity – as we have already seen, the separation itself is a problematic assertion. Nor should we take practical activity or contemplation to be specific to such a relation. The Heideggerian strategy is a reversal of priorities, now it’s doing over knowing and not knowing over doing. The point of this is to clear the ground for the question of the way of being of intentionality. It is not a dichotomy between practical and theoretical forms of intentionality. Heidegger wanted to burst out of the tradition. He aimed to overcome the subject-object distinction in all domains and move on from the old account of intentionality altogether.
Heidegger accepted that there is an intentional directedness to human activity, but rejected the Husserlian view that the mind is directed towards an object which mirrors an object in the external world. Practical engagement is important, though we have to go above and beyond practical activity to raise the question of Being. The problem is the gap which is allowed to open up between the subject and object, the directedness which Husserl puts forth is meant to resolve this problem. But it just exacerbates the problem as it maintains intentionality as a feature of mental states. Intentionality is not mental, as it is for Husserl, it should not be attributed to consciousness but Dasein – which is being-in-the-world – and in that sense refers to human activity at a more general level in that the practical intention goes through the thing we use towards the purpose of the activity. The directedness is in the embedded nature of being-in-the-world, it is a part of the human existence and undoubtedly an aspect of the dialogue between the human subject and the world (if we must refer back to that troublesome distinction).
In the attempt to overcome the old notion of intentionality Heidegger opens up a new kind of intentionality. Similarly with Heidegger’s ‘confrontation’ with Friedrich Nietzsche – who he deemed responsible for the ‘end of metaphysics’ – could only be conducted within the framework of another metaphysical system just as Nietzsche had opened up a metaphysics of becoming in the attempt to overcome metaphysics. Even the conscious attempt to overcome a philosophical tradition fails to do so insofar as it may succeed, but in doing so reconstitute the system that was meant to be overcome. It may even be that the move Heidegger made to critique Cartesianism and ultimately transcend the subject-object distinction might have only perpetuating, or more accurately, recreated the old distinction in the act of trying to sweep it away. The account Heidegger provided of being-in-the-world is important as it is part of the philosophical project through which he attempted to radically reorder philosophy as it has been since Socrates. This is the greater importance to which the significance the concept has in relation to existentialism and phenomenology is just an addition.
 Dreyfus, Hubert: Being-in-the-World: A Commentary on Heidegger’s Being and Time, Division 1 (MIT Press, 1991) pg.30-39
 Becker, Oskar: The Philosophy of Edmund Husserl, Elveton, RO: The Phenomenology of Husserl (Chicago Quadrangle Books, 1970) pg.60-71
 Ludwig Wittgenstein (who had a great deal in common with Heidegger in his later philosophy) was perplexed by the very notion of an external world and what it is supposed to be external to specifically. Heidegger had this in common with Wittgenstein as he conceived of being-in-the-world to signify the human existence as bound up with reality, both as constitutive and constituted by it. So the suggestion that there is a world ‘out there’ which can be analysed is quite strange from this perspective. Whereas Husserl concedes that there is a world external to thought and experience insofar as objects can transcend our consciousness.
 We might be drawn to Hume’s sceptical view that there could be more than just the experiential, but we cannot know if there is. The difference is that for Husserl it is not that these things are beyond our knowledge; rather we should exclude them in order to get back to the things themselves. But it should be noted that this kind of phenomenology is not another form of empiricism.
 In a way Descartes held that we can step outside of being-in-the-world where an object can be placed before a subject. For Heidegger it is important to reject the Cartesian tradition because it seemed utterly hopeless to him. This might explain why he avoided talk of subjectivity as well as consciousness and the mind without the use of his own meta-language. Note that Heidegger saw our basic experiences as a holistic and unified experience of our being-in-the-world. Descartes propagated dualism, which posited a mind-body separation which can both be encompassed by Being for Heidegger. Cartesianism is a road with a dead-end for Heidegger, the separation between being-in-the-world and something else (e.g. consciousness and the external world) leads us to paradoxical ways of thinking. To understand Dasein is to understand the world and it works both ways, Dasein and the world are a unified phenomenon according to Heidegger. So the self cannot exist independently of the physical world, there can be no Dasein without the world and no world without Dasein.
Solomon, Robert: Lecture Fifteen; Husserl, Heidegger and Phenomenology.
 Eagleton, Terry: Literary Theory: An Introduction (Blackwell Publishers Ltd, 1983 | Second Edition, 1983) pg.47-78
 Solomon, Robert: Lecture Fifteen; Husserl, Heidegger and Phenomenology.
 Dreyfus, Hubert: Being-in-the-World: A Commentary on Heidegger’s Being and Time, Division 1 (MIT Press, 1991) pg.238-246
 In Goethe’s Faust the role of care is important as it refers to the burdens of worry and the world explicitly. Heidegger uses care in a much more radical way, it is not only about ends and purposes but about the world as equipment where we engage in tasks. The world is not a field of objects and subjects which might interact. To see the hammer and the plank as ‘things’ means that we would have to stop hammering, the hammer is no longer just something used for a purpose along with the nail and the plank serves as a material to work with.
Incidentally, for Nietzsche Goethe was an example of the Übermensch and the Will to Power who exercised all of his talents, ‘created’ himself as a unified being through his art and he experimented in life – taking jobs as a civil servant and a lawyer, as well as a playwright and a poet. As a writer he flirted with many styles and his works are voluminous. In Nietzsche’s terms the passion for life is the greatest of passions and Goethe was passionate at a creative and spiritual level. Nietzsche describes Goethe as “not a German event but a European one: a grand attempt to overcome the eighteenth century through a return to nature, through a going-up to the naturalness of the Renaissance, a kind of self-overcoming on the part of that century.”
Nietzsche, Friedrich; Twilight of the Idols and The Anti-Christ (Hollingdale, RJ; Introduction and commentary | Penguin Books, 1968) pg.102-104
Solomon, Robert: Lecture Sixteen; Heidegger on the World and the Self.
 Heidegger seems to take a very similar response to the question of free-will as that of Karl Marx (someone he no doubt detested for political as well as philosophical reasons). We might think in particular of Marx’s words “Men make their own history, but not of their own free will; not under circumstances they themselves have chosen but under the given and inherited circumstances with which they are directly confronted.” This is where Heidegger is actually closer to Marx than he is to Sartre.
Marx, Karl: The Eighteenth Brumaire of Louis Bonaparte, Surveys from Exile: Political Writings vol.2 (Edited and introduced by David Fernbach, Verso, 2010) pg.143-150
 Solomon, Robert: Lecture Sixteen; Heidegger on the World and the Self.
 Wartenberg, Thomas: Existentialism (Oneworld Publications, 2008) pg.125-145
 Dreyfus, Hubert: Being-in-the-World: A Commentary on Heidegger’s Being and Time, Division 1 (MIT Press, 1991) pg.40-54
 As Harrison Hall points out, using the most famous example, the hammer has perceivable properties which go unrecognised when the hammer is being skilfully employed and only arise when we take a timeout from the task to think about the hammer. The attention is aimed at the work and the ultimate end, but not the equipment which enables us to do so. The function of the hammer is in the practical activity to which it is used and that is definitive of their being. We can spot this network of relations essential to their instrumental nature whenever the task breaks down. We find that the ready-to-hand tools are always pointing towards an end, which we assign in the task.
The Cambridge Companion to Heidegger: Hall, Harrison: Intentionality and World pg.123-139
 Sluga, Hans: Heidegger’s Nietzsche pg.110-113