first they think that knowledge' rather than 'the problem of being' is the central problem of philosophy, the second is that a sharp distinction can be drawn between what we experience and the 'importance' or 'value' we attach to it.  

Professing to be ontology-free, such an  empiricism', Heidegger argues, in fact rests on an ontology which, if taken seriously, gives rise to insuperable problems.  

Roughly speaking, empiricism presumes that the world falls apart into two classes of entities -'subjects' whose principal task it is to perceive and 'objects' whose character it is to be perceived.  

So perception, according to the empiricist, is the link between two ontologically isolated forms of substance.  But then, according to Heidegger, it is impossible to show how any link could possibly connect substances so disparate, how, for example, a 'spiritual substance' could ever perceive an 'external' world'.

As soon as we ask what it is that is demanding a proof of the external world, we see at once, according to Heidegger, that it is already a 'being-in-the-world'.  Only the impossible ontological presumption that questions about the external world could be asked by an isolated self enables the empiricist to suppose that the existence of the external world could ever be a real problem.

Similarly, Heidegger argues, the classical problem of truth arises out of the presumption that truth is a property of some entity, or set of entities, which lies between us and the world; the insuperable problem which then arises is how such entities could 'correspond' to anything in the world.  

In fact, according to Heidegger, truth is a 'revelation', a 'showing forth': 'That hammer is too heavy', for example, is true if the hammer reveals itself as being too heavy - there is no third entity between ourselves and the heaviness of the hammer to which the 'too-heaviness' of the hammer somehow 'corresponds'.
Heidegger's choice of example is significant.  British empiricism 
takes as its typieal instances of 
what we notice in the world such 
facts as 'the grass is green', or, in the more sophisticated forms of empiricism, 'that thing over there 
looks green'.  These examples at once suggest that our interest in the 
world is that of a spectator, a looker-on.  'The hammer is too heavy'
in contrast, suggests as typical a 
quite different, more practical, attitude to the world, for which the things around us are tools, 
'equipment', things which are 'ready-to-hand', as distinct from 
merely 'present-at-hand'.

Perception, being content to be a looker-on, is, for Heidegger, a rare form of 'care', not the typical mode of being-in-the-world. (Contrast Berkeley for whom the whole being of objects consists in their being perceived.) 

Nor is it, according to Heidegger, the essence of the mind to perceive  to look at things impartially.  

When we look at the world, he argues, we are always 'in a certain mood'.  Men talk of overcoming their moods, but what really happens in such cases, according to Heidegger, is that one mood overcomes another.  Even apathy is a mood, not the absence of a mood.  We encounter the world as something 'attuned' to our mood; the world for us is always something we value or despise.  

We do not first see it and then attach a value to it; what we see and how we see it depends on what we are at that moment taking to be valuable.
We encounter other people, too, not as inferences from what we perceive, but as owners of, and fellow-users of, 'equipment'.  Other people are not just there to be looked at.  Even when they are 'standing around', this - unlike the immobility of a statue is itself a way of behaving, a rejection of what surrounds them as inutilizable.  'The others,' so Heidegger sums up, 'are what they do' - we know them as agents, and in the process of observing their agency we come to know our own powers as an agent.

Indeed, in its most characteristic, 'everyday' form, Human Existence consists not in being oneself - revealing one's own Existenz - but in being 'They' (or as the German illuminatingly has it, Man).  In our everyday 'average' life we act as 'the others' act, not because we have deliberately chosen to conform to 'the tasks, the rules, the standards, the urgency' of others, but simply because 'acting as They do' is the typical mode of behaviour of Human Existence.

'Acting as They do', however, although 'everyday' is nonetheless 'inauthentic'.  Like Kierkegaard and Jaspers, Heidegger suggests that we are aroused out of this inauthenticity by encountering 'ultimate situations' and, in particular, by our realization that we must die, a realisation which has to Heidegger a crucial significance.  

Most of the situations in which we can contemplate our finding ourselves are of such a kind that we can easily think of its being someone else rather than ourselves who is involved in them; we can easily imagine that it is a friend,rather than ourselves, who takes a holiday in Rome, or writes a successful book, or, even, suffers the death of his child.  But the case of our own death, according to Heidegger, is very different; in death it is my Human Existence which comes to an end, it is my potentialities which are exhausted.  Nobody else can - in the sense which is now in question - die for me.  I can, of course, try to forget that I will die, in the 'idle chatter' of everyday existence; but only by not forgetting it, by holding tight to the fact of mortality, can I preserve my authenticity. 

In the phenomena of guilt and conscience, too, we come to recognize our own Existenz.  Conscience, Heidegger argues, cannot be reduced to 'the voice of God' or 'the voice of the people'; these are attempts to cope with conscience inauthentically, to convert it into something 'They' say to us.  There is, Heidegger admits, some excuse for such an interpretation of conscience.  

Phenomenologically, conscience calls to me as if it were both from me and from beyond me; that is why it is natural, concentrating on the second aspect of its manner of calling, to ascribe that call to somebody else.  But the call of consciencc seems alien to us only because we are ordinarily so absorbed within that impersonal life which 'one' lives, I do not recognize that in conscience I am calling myself, because the call comes not from my everyday self, but from my'uncanny'self.

What is the 'uncanny' self?  Heidegger first introduces this concept as part of his phenomenological analysis of 'anxiety'.  He distinguishes sharply between anxiety and fear, on the ground that in anxiety we are not afraid of a definite possibility, as we might be afraid of being run over when we cross the Place de la Concorde; we are afraid of nothing in particular.  Or as we might also put the matter, we are anxious about 'what the world might do to us' - we no longer feel at home in the world. (Heidegger exploits the fact that the German word for'uncanny'is'unheimlich', from the root-word'heim', meaning'home').

Now we begin to see how Heidegger introduces the conception of Nothing.  In anxiety what are we afraid of ? Nothing.  And what is the authentic self, in its permanent character?  Nothing.  What, in conscience, calls to us?  Nothing.  This at least, so Heidegger suggests, is'how we must reply to such questions so long as we are expected to reply in an everyday, 'worldly' way - for we cannot answer them by referring to that sort of definite particularized entity which is the staple of everyday 'being-in-the-world'. 

Our authentic 'self' is a potentiality for action, not an agent in the ordinary sense of the word; 'conscience' is the call of our potentialities, not the call of a person. The guilt for which conscience rebukes us, Heidegger argues, is not a 'worldly-guilt' for not having done what 'They' want us to do - not having paid a debt, for example - it is a guilt for what we have not done, for our failure to be what we migbt have been. We feel guilty, that is, about 'nothing'. 

A central phenomenological fact about Human Existence, according to Heidegger, is its temporality, its historicity. This, he suggests, is one of the points at which both phenomenology and scholasticism break down; they neither of them recognize the historicity of Being. Just for that reason they are powerless against Marxism, which to some degree does so. But to say that Human Existence is 'historical' is to say a great deal more than that, as Marxists suggest, human beings are 'a more or less important atom in world-history'. Human Existence, according to Heidegger, is through-and-through temporal. It lives in anticipation - in particular in the anticipation of its own death; it finds things 'useful' for the future or 'worn-out' from their past. 

On the traditional view, human beings live in the present and reach towards the past and the future only by way of recollection or prediction. For Heidegger this is true, and even then with reservations, only of inauthentic Human Existence - which, indeed, tries to think of the future and the past as if it were only the present all over again. 

But the fundamental mode of being of Human Existence, according to Heidegger, is in the future. This conclusion follows directly from Heidegger's phenomenological analysis of Human Existence, for which 'care' is central, and from his emphasis on our own future death as the critically important 'ultimate situation'. But the past is, on his view, of scarcely less vital import than the future. Human Existence is not merely fatalistic in its attitude to the fact that it must die; out of its recognition of its mortality, out of its sense of guilt, of not having achieved what it might have been, it develops 'resoluteness'. And this 'resoluteness', although directed towards the future, derives its confidence, Heidegger suggests, from a return to the past, from the possibility of taking a 'hero' from the past, of 'repeating' what has been done before, not in the sense of doing just that thing again, but as responding to those possibilities which were inherent in it but which were not realized. It is characteristic of the 'hero' that in his deeds or in his thoughts there is this reserve of as yet unrealized possibilities. 

We have not exhausted what, for example, Parmenides can mean to us. No doubt the 'everyday' present, Heidegger admits, already in some measure absorbs the past. But the 'resolute' self finds itself compelled to 'disavow' the present in order to return to the past, to see the past in terms of the unrealized possibilities it still presents. This, it becomes elear in the outcome, is Heidegger's 'vision' of his own 'destiny' as a philosopher. More and more he returns to the past, especially to the early Greek philosophers, but not in the spirit of a scholar: his object is to complete the task which they initiated but which men later 'forgot'. 

What has so far been said about Being and Time is in a fundamental respect highly misleading; for it would suggest that Being and Time is purely and simply a contribution to existentialism. But Heidegger has explicitly denied that be is an existentialist. 'My philosophical tendencies,' he wrote in a letter to Jean Wahl, 'cannot be classified as existentialist; the question which principally concerns me is not that of man's Existenz; it is Being in its totality and as such.' 

That fact, indeed, is made perfectly clear at the very outset of his work "Being and Time". Heidegger takes as his point of departure, not Kierkegaard's analysis of Existenz, but a passage from Plato's "The Sophist" - a passage which he translates as follows: 

'For you have long been aware of what you mean when you use theexpression "being". We, however, who used to think we understood it, have now become perplexed.' 

Everybody, Heidegger agrees with Plato, must in some sense know what he means when be says of something 'it is'. But philosophy, Plato says, has become perplexed about the meaning of being; it is that perplexity which Heidegger hopes to understand and to resolve. 

Philosophy, he argues, must return to the problem of Being; a problem which Plato himself put fatally in the wrong light in so far as he identified Being with certain particular beings - the Ideas or the Forms. 

Heidegger is well aware that the question 'What is Being ?'has been denounced as senseless. Nietzsche, who is in Heidegger's eyes the culminating figure in Western metaphysics, had explicitly maintained that Being is an empty idea - 'the last cloudy streak of evaporating reality'. 

In his Introduction to Metaphysics (1953, English translation 1959) Heidegger set out to answer Nietzsche. Man cannot do without the conception of Being, according to Heidegger; without it be would be speechless. 'There would, indeed, be no language at all' and in consequence no Human Existence, since man is essentially a language user. In order to speak at all, we have to be able to say of things that they 'are'. No doubt, they 'are' in quite different fashions - the -'is' of 'the lecture is in the Auditorium' is not identical with the 'is' of 'the book is mine' or of 'the red is the port side' or of 'God is' - but that is only to say, according to Heidegger, that Being manifests itself in various ways. 

If its real theme is 'the meaning of Being', why is so much of Heidegger's Being and Time devoted to Human Existence? 

Human Existence, Heidegger argues, is peculiarly important to ontology, just because the human being has - in the sense to which Plato drew attention -'a vague average understanding of Being'. By his nature as a language-user, as an inquirer, as the only being who is conscious that he is one day not to be, as 'solicitous' for others, solicitous for what they have it in them to be, the human being 'cares' for Being. 

So, by studying Human Existence the philosopher is led directly to Being. One reason why Being and Time has so often been read as a variety of existentialism is that it is incomplete; Heidegger never published those final sections, although he several times directs his readers to them, in which the meaning of Being was to be made clear. So the first sections of Being and Time, which were intended only as a foundation for a 'hermeneutics' in which the nature of Being would be 'read off' from the analysis of Human Existence there provided, constitute, in the outcome, its whole. 

Thus it is that Heidegger becomes, one might say, an existentialist in spite of himself. Nor does Heidegger in his later writings - essays and lectures,many of them very brief - supply the missing finale to Being and Time. The 'quest for being' traditionally takes the form of ontology and metaphysics. But although in Being and Time Heidegger is happy to describe what he hoped to achieve as 'ontology', be came to feel that this was a misleading description of it; so be was led to reject ontology. 

Metaphysics, he argued in his introduction to the 1949 edition of What is Metaphysics? has also to be I overcome'. 'Due to the manner in which it thinks of being,' he there writes, 'metaphysics almost seems to be, without knowing it, the barrier which keeps Man from the involvement of Being in human nature'. 

The difficulty, in Heidegger's eyes, is that both metaphysics and ontology substitute a particular characteristic or a particular entity for Being itself; in the typical 'worldly' fashion they confuse Being with a being, whether they identify it with God or the form of the good or the 'highest genus'. 

This does not mean that metaphysics and ontology have simply to be condemned; there is much to be learnt from them, Heidegger thinks, but in the end one must disavow them and return to their grounds. 

Even philosophy, be suggests in his "Woodman's Trails" if that, rather than Blind Alleys, is the best translation of Holzwege (1950) - is the 'enemy of thinking'. ('Thinking' now has the special meaning of 'thinking about Being'.) If we were to say of these late writings, as many of us would like to do, that in them Heidegger is 'not a philosopher at all', Heidegger would, it seems, be in perfect agreement with us. 

Then what path does Heidegger recommend to us? Being and Time tried to approach Being through Human Existence, and in his essay on Identity and Difference (1957, English translation 1960) Heidegger still argues that 'only in Man can Being be domiciled', that 'Man alone has made himself accessible to Being'. 

But Being is not to be reached, it would seem, by the path of phenomenological analysis. We shall not find it by a painstaking search but rather by letting it reveal itself to us. Heidegger turned then to poetry, and especially to the poetry of Hölderlin.

'Poetry,'so he wrote in an essay on Hölderlin,'is the establishment of Being by means of the word.' He never abandons that view; in Heidegger's later writings, the poet has the same authority as the philosopher, and Parmenides'poem about being, not the Platonic dialogue, is the exemplar of philosophy.