• Philosopher and Mathematician Martin Heidegger, 1889

Heidegger maintained that philosophy, in the process of philosophizing, had lost sight of the being it sought. Finding ourselves "always already" fallen in a world of presuppositions we lose touch with what being was before its truth became "muddled". Our way of questioning defines our nature. He advocated a return to the practical being in the world, allowing it to reveal, or "unconceal" itself as concealment.

Writing extensively on Nietzsche in his later career, and offering a "phenomenological critique of Kant" in his Being and Time (1927), Heidegger is known for his Post - Kantian philosophy. His best known book, Being and Time is considered one of the most important philosophical works of the 20th century. Heidegger's influence has been far reaching, from philosophy to theology, deconstructionism, literary theory, architecture and artificial intelligence.

Heidegger is a controversial figure, largely for his affiliation with the Nazis, for which he never apologized nor expressed regret, except in private when he called it "the biggest stupidity of his life" (die größte Dummheit seines Lebens). The so-called Heidegger controversy raises general questions about the relation between Heidegger's thought and his connection to National Socialism.

Heidegger claimed that Western philosophy since Plato has misunderstood what it means for something "to be", tending to approach this question in terms of a being, rather than asking about Being itself. In other words, Heidegger believed all investigations of being have historically focused on particular entities and their properties, or have treated Being itself as an entity, or substance, with properties. A more authentic analysis of being would, for Heidegger, investigate "that on the basis of which beings are already understood," or that which underlies all particular entities and allows them to show up as entities in the first place. But since philosophers and scientists have overlooked the more basic, pre - theoretical ways of being from which their theories derive, and since they have incorrectly applied those theories universally, they have confused our understanding of being and human existence. To avoid these deep rooted misconceptions, Heidegger believed philosophical inquiry must be conducted in a new way, through a process of retracing the steps of the history of philosophy.

Heidegger argued that this misunderstanding, beginning with Plato, has left its traces in every stage of Western thought. All that we understand, from the way we speak to our notions of "common sense", is susceptible to error, to fundamental mistakes about the nature of being. These mistakes filter into the terms through which being is articulated in the history of philosophy - such as reality, logic, God, consciousness and presence. In his later philosophy, Heidegger argues that this profoundly affects the way in which human beings relate to modern technology.

The Internet Encyclopedia of Philosophy states that his writing is 'notoriously difficult', possibly because his thinking was 'original' and clearly on obscure and innovative topics. Heidegger accepted this charge, stating 'Making itself intelligible is suicide for philosophy', and suggesting that intelligibility is what he is critically trying to examine.

Heidegger's work has strongly influenced philosophy, aesthetics of literature, and the humanities. Within philosophy it played a crucial role in the development of existentialism, hermeneutics, deconstructionism, postmodernism, and continental philosophy in general. Well known philosophers such as Karl Jaspers, Leo Strauss, Ahmad Fardid, Hans - Georg Gadamer, Jean - Paul Sartre, Emmanuel Lévinas, Hannah Arendt, Maurice Merleau - Ponty, Michel Foucault, Richard Rorty, William E. Connolly and Jacques Derrida have all analyzed Heidegger's work.

Heidegger supported National Socialism in 1933 and was a member of the Nazi Party until May 1945, even though the Nazis eventually prevented him from teaching. His defenders, notably Hannah Arendt, see this support as arguably a personal " 'error' " (a word which Arendt placed in quotation marks when referring to Heidegger's Nazi era politics). Defenders think this error was irrelevant to Heidegger's philosophy. Critics, such as Emmanuel Levinas and Karl Löwith, claim that Heidegger's support for National Socialism revealed flaws inherent in his thought.

Heidegger was born in rural Meßkirch, Germany. Raised a Roman Catholic, he was the son of the sexton of the village church, Friedrich Heidegger, and his wife Johanna, née Kempf. In their faith, his parents adhered to the First Vatican Council of 1870, which was observed mainly by the poorer class of Meßkirch. The religious controversy between the wealthy Altkatholiken and the working class led to the temporary use of a converted barn for the Roman Catholics. At the festive reunion of the congregation in 1895, the Old Catholic sexton handed the key to six year old Martin.

Heidegger's family could not afford to send him to university, so he entered a Jesuit seminary, though he was turned away within weeks because of the health requirement and what the director and doctor of the seminary described as a psychosomatic heart condition. Heidegger later left Catholicism, describing it as incompatible with his philosophy. After studying theology at the University of Freiburg from 1909 to 1911, he switched to philosophy, in part again because of his heart condition.

Heidegger completed his doctoral thesis on psychologism in 1914 influenced by Neo - Thomism and Neo - Kantianism, and in 1916 finished his venia legendi with a thesis on Duns Scotus influenced by Heinrich Rickert and Edmund Husserl. In the two years following, he worked first as an unsalaried Privatdozent, then served as a soldier during the final year of World War I, working behind a desk and never leaving Germany. After the war, he served as a salaried senior assistant to Edmund Husserl at the University of Freiburg in the Black Forest from 1919 until 1923.

In 1923, Heidegger was elected to an extraordinary Professorship in Philosophy at the University of Marburg. His colleagues there included Rudolf Bultmann, Nicolai Hartmann and Paul Natorp. Heidegger's students at Marburg included Hans - Georg Gadamer, Hannah Arendt, Karl Löwith, Gerhard Krüger, Leo Strauss, Jacob Klein, Gunther (Stern) Anders and Hans Jonas. Through a confrontation with Aristotle he began to develop in his lectures the main theme of his philosophy: the question of the sense of being. He extended the concept of subject to the dimension of history and concrete existence, which he found prefigured in such Christian thinkers as Saint Paul, Augustine of Hippo, Luther and Kierkegaard. He also read the works of Dilthey, Husserl and Max Scheler.

In 1927, Heidegger published his main work Sein und Zeit (Being and Time). When Husserl retired as Professor of Philosophy in 1928, Heidegger accepted Freiburg's election to be his successor, in spite of a counter offer by Marburg. Heidegger remained at Freiburg im Breisgau for the rest of his life, declining a number of later offers, including one from Humboldt University of Berlin. His students at Freiburg included Charles Malik, Herbert Marcuse and Ernst Nolte. Emmanuel Levinas attended his lecture courses during his stay in Freiburg in 1928.

Heidegger was elected rector of the University on April 21, 1933, and joined the National Socialist German Workers' (Nazi) Party on May 1. In his inaugural address as rector on May 27 he expressed his support to a German revolution, and in an article and a speech to the students from the same year he even supported Adolf Hitler. However, he resigned the rectorate in April 1934, but remained a member of the Nazi party until 1945, even though the Nazis eventually prevented him from teaching.

In late 1946, as France engaged in épuration légale, the French military authorities determined that Heidegger should be forbidden from teaching or participating in any university activities because of his association with the Nazi Party. The denazification procedures against Heidegger continued until March 1949, when he was finally pronounced a "Mitläufer" (literally, mit = with, Läufer = runner, i.e., "one who runs along with", but the equivalent meaning in English is closer to "bandwagon effect" or "herd instinct", standing for the notion that people often do and believe things merely because many other people do and believe the same things) of National Socialism, and no punitive measures against him were proposed. This opened the way for his readmission to teaching at Freiburg University in the winter semester of 1950 – 51. He was granted emeritus status and then taught regularly from 1951 until 1958, and by invitation until 1967.

Heidegger married Elfride Petri on March 21, 1917, in a Catholic ceremony officiated by his friend Engelbert Krebs, and a week later in a Protestant ceremony in the presence of her parents. Their first son Jörg was born in 1919. According to published correspondence between the spouses, Hermann (born 1920) is the son of Elfride and Friedel Caesar.

Martin Heidegger had extramarital affairs with Hannah Arendt and Elisabeth Blochmann, both students of his. Arendt was Jewish, and Blochmann had one Jewish parent, making them subject to severe persecution by the Nazi authorities. He helped Blochmann emigrate from Germany prior to World War II, and resumed contact with both of them after the war.

Heidegger spent much time at his vacation home at Todtnauberg, on the edge of the Black Forest. He considered the seclusion provided by the forest to be the best environment in which to engage in philosophical thought.

Heidegger died on May 26, 1976, and was buried in the Meßkirch cemetery.

Heidegger's philosophy is founded on the attempt to conjoin what he considers two fundamental insights: the first is his observation that, in the course of over 2,000 years of history, philosophy has attended to all the beings that can be found in the world (including the "world" itself), but has forgotten to ask what "being" itself is. This is Heidegger's "question of being," and it is Heidegger's fundamental concern throughout his work. One crucial source of this insight was Heidegger's reading of Franz Brentano's treatise on Aristotle's manifold uses of the word "being," a work which provoked Heidegger to ask what kind of unity underlies this multiplicity of uses. Heidegger opens his magnum opus, Being and Time, with a citation from Plato's Sophist indicating that Western philosophy has neglected "being" because it was considered obvious, rather than as worthy of question. Heidegger's intuition about the question of being is thus a historical argument, which in his later work becomes his concern with the "history of being," that is, the history of the forgetting of being, which according to Heidegger requires that philosophy retrace its footsteps through a productive "destruction" of the history of philosophy.

The second intuition animating Heidegger's philosophy derives from the influence of Edmund Husserl, a philosopher largely uninterested in questions of philosophical history. Rather, Husserl argued that all that philosophy could and should be a description of experience (hence the phenomenological slogan, "to the things themselves"). But for Heidegger, this meant understanding that experience is always already situated in a world and in ways of being. Thus Husserl's understanding that all consciousness is "intentional" (in the sense that it is always intended toward something, and is always "about" something) is transformed in Heidegger's philosophy, becoming the thought that all experience is grounded in "care."

This is the basis of Heidegger's "existential analytic", as he develops it in Being and Time. Heidegger argues that to describe experience properly entails finding the being for whom such a description might matter. Heidegger thus conducts his description of experience with reference to "Dasein," the being for whom being is a question.

In Being and Time, Heidegger criticized the abstract and metaphysical character of traditional ways of grasping human existence as rational animal, person, man, soul, spirit or subject. Dasein, then, is not intended as a way of conducting a philosophical anthropology, but is rather understood by Heidegger to be the condition of possibility for anything like a philosophical anthropology. Dasein, according to Heidegger, is care. In the course of his existential analytic, Heidegger argues that Dasein, who finds itself thrown into the world amidst things and with others, is thrown into its possibilities, including the possibility and inevitability of one's own mortality. The need for Dasein to assume these possibilities, that is, the need to be responsible for one's own existence, is the basis of Heidegger's notions of authenticity and resoluteness — that is, of those specific possibilities for Dasein which depend on escaping the "vulgar" temporality of calculation and of public life.

The marriage of these two observations depends on the fact that each of them is essentially concerned with time. That Dasein is thrown into an already existing world and thus into its mortal possibilities does not only mean that Dasein is an essentially temporal being; it also implies that the description of Dasein can only be carried out in terms inherited from the Western tradition itself. For Heidegger, unlike for Husserl, philosophical terminology could not be divorced from the history of the use of that terminology, and thus genuine philosophy could not avoid confronting questions of language and meaning. The existential analytic of Being and Time was thus always only a first step in Heidegger's philosophy, to be followed by the "dismantling" (Destruktion) of the history of philosophy, that is, a transformation of its language and meaning, that would have made of the existential analytic only a kind of "limit case" (in the sense in which special relativity is a limit case of general relativity).

That Heidegger did not write this second part of Being and Time, and that the existential analytic was left behind in the course of Heidegger's subsequent writings on the history of being, might be interpreted as a failure to conjugate his account of individual experience with his account of the vicissitudes of the collective human adventure that he understands the Western philosophical tradition to be. And this would in turn raise the question of whether this failure is due to a flaw in Heidegger's account of temporality, that is, of whether Heidegger was correct to oppose vulgar and authentic time.

Being and Time (German title: Sein und Zeit), published in 1927, is Heidegger's first academic book. He had been under pressure to publish in order to qualify for Husserl's chair at University of Freiburg and the success of this work ensured his appointment to the post.

It investigates the question of being by asking about the being for whom being is a question. Heidegger names this being Dasein, and the book pursues its investigation through themes such as mortality, care, anxiety, temporality and historicity. It was Heidegger's original intention to write a second half of the book, consisting of a "Destruktion" of the history of philosophy — that is, the transformation of philosophy by re-tracing its history — but he never completed this project.

Being and Time influenced many thinkers, including such existentialist thinkers as Jean - Paul Sartre (although Heidegger distanced himself from existentialism).

Heidegger's later works, after the Second World War, seem to many commentators (e.g., William J. Richardson) to at least reflect a shift of focus, if not indeed a major change in his philosophical outlook. One way this has been understood is as a shift from "doing" to "dwelling". However, others feel that this is to overstate the difference. For example, in 2011 Mark Wrathall argued that Heidegger pursued and refined the central notion of unconcealment throughout his life as a philosopher. Its importance and continuity in his thinking, Wrathall states, shows that he did not have a 'turn'. A reviewer of Wrathall's book stated: "An ontology of unconcealment ... means a description and analysis of the broad contexts in which entities show up as meaningful to us, as well as the conditions under which such contexts, or worlds, emerge and fade."

Heidegger focuses less on the way in which the structures of being are revealed in everyday behavior, and more on the way in which behavior itself depends on a prior "openness to being." The essence of being human is the maintenance of this openness. Heidegger contrasts this openness to the "will to power" of the modern human subject, which is one way of forgetting this originary openness.

Heidegger understands the commencement of the history of Western philosophy as a brief period of authentic openness to being, during the time of the pre - Socratics, especially Anaximander, Heraclitus and Parmenides. This was followed, according to Heidegger, by a long period increasingly dominated by the forgetting of this initial openness, a period which commences with Plato, and which occurs in different ways throughout Western history.

Two recurring themes of Heidegger's later writings are poetry and technology. Heidegger sees poetry and technology as two contrasting ways of "revealing." Poetry reveals being in the way in which, if it is genuine poetry, it commences something new. Technology, on the other hand, when it gets going, inaugurates the world of the dichotomous subject and object, which modern philosophy commencing with Descartes also reveals. But with modern technology a new stage of revealing is reached, in which the subject - object distinction is overcome even in the "material" world of technology. The essence of modern technology is the conversion of the whole universe of beings into an undifferentiated "standing reserve" (Bestand) of energy available for any use to which humans choose to put it. Heidegger described the essence of modern technology as Gestell, or "enframing." Heidegger does not unequivocally condemn technology: while he acknowledges that modern technology contains grave dangers, Heidegger nevertheless also argues that it may constitute a chance for human beings to enter a new epoch in their relation to being. Despite this, some commentators have insisted that an agrarian nostalgia permeates his later work.

In a 1950 lecture he formulated the famous saying Language speaks, later published in the 1959 essays collection Unterwegs zur Sprache, and collected in the 1971 English book Poetry, Language, Thought.

Heidegger's later works include Vom Wesen der Wahrheit ("On the Essence of Truth", 1930), Der Ursprung des Kunstwerkes ("The Origin of the Work of Art", 1935), Einführung in die Metaphysik ("Introduction to Metaphysics", 1935), Bauen Wohnen Denken ("Building Dwelling Thinking", 1951), and Die Frage nach der Technik ("The Question Concerning Technology", 1954) and Was heisst Denken? ("What Is Called Thinking?" 1954). Also Beiträge zur Philosophie (Vom Ereignis) (Contributions to Philosophy (From Enowning)), composed in the years 1936 – 38 but not published until 1989, on the centennial of Heidegger's birth.

Recent scholarship has shown that Heidegger was substantially influenced by St. Augustine of Hippo and that Martin Heidegger's Being and Time would not have been possible without the influence of Augustine's thought. Augustine's Confessions was particularly influential in shaping Heidegger's thought.

Heidegger was influenced at an early age by Aristotle, mediated through Catholic theology, medieval philosophy and Franz Brentano. Aristotle's ethical, logical and metaphysical works were crucial to the development of his thought in the crucial period of the 1920s. Although he later worked less on Aristotle, Heidegger recommended postponing reading Nietzsche, and to "first study Aristotle for ten to fifteen years." In reading Aristotle, Heidegger increasingly contested the traditional Latin translation and scholastic interpretation of his thought. Particularly important (not least for its influence upon others, both in their interpretation of Aristotle and in rehabilitating a neo - Aristotelian "practical philosophy") was his radical reinterpretation of Book Six of Aristotle's Nicomachean Ethics and several books of the Metaphysics. Both informed the argument of Being and Time.

The idea of asking about being may be traced back via Aristotle to Parmenides. Heidegger claimed to have revived the question of being, the question having been largely forgotten by the metaphysical tradition extending from Plato to Descartes, a forgetfulness extending to the Age of Enlightenment and then to modern science and technology. In pursuit of the retrieval of this question, Heidegger spent considerable time reflecting on ancient Greek thought, in particular on Plato, Parmenides, Heraclitus and Anaximander, as well as on the tragic playwright Sophocles.

Heidegger's very early project of developing a "hermeneutics of factical life" and his hermeneutical transformation of phenomenology was influenced in part by his reading of the works of Wilhelm Dilthey.

Of the influence of Dilthey, Hans - Georg Gadamer writes the following: "As far as Dilthey is concerned, we all know today what I have known for a long time: namely that it is a mistake to conclude on the basis of the citation in Being and Time that Dilthey was especially influential in the development of Heidegger's thinking in the mid 1920s. This dating of the influence is much too late." He adds that by the fall of 1923 it was plain that Heidegger felt "the clear superiority of Count Yorck over the famous scholar, Dilthey." Gadamer nevertheless makes clear that Dilthey's influence was important in helping the youthful Heidegger "in distancing himself from the systematic ideal of Neo - Kantianism, as Heidegger acknowledges in Being and Time." Based on Heidegger's earliest lecture courses, in which Heidegger already engages Dilthey's thought prior to the period Gadamer mentions as "too late", scholars as diverse as Theodore Kisiel and David Farrell Krell have argued for the importance of Diltheyan concepts and strategies in the formation of Heidegger's thought.

Even though Gadamer's interpretation of Heidegger has been questioned, there is little doubt that Heidegger seized upon Dilthey's concept of hermeneutics. Heidegger's novel ideas about ontology required a gestalt formation, not merely a series of logical arguments, in order to demonstrate his fundamentally new paradigm of thinking, and the hermeneutic circle offered a new and powerful tool for the articulation and realization of these ideas.

There is disagreement over the degree of influence that Husserl had on Heidegger's philosophical development, just as there is disagreement about the degree to which Heidegger's philosophy is grounded in phenomenology. These disagreements center around how much of Husserlian phenomenology is contested by Heidegger, and how much this phenomenology in fact informs Heidegger's own understanding.

On the relation between the two figures, Gadamer wrote: "When asked about phenomenology, Husserl was quite right to answer as he used to in the period directly after World War I: 'Phenomenology, that is me and Heidegger'." Nevertheless, Gadamer noted that Heidegger was no patient collaborator with Husserl, and that Heidegger's "rash ascent to the top, the incomparable fascination he aroused, and his stormy temperament surely must have made Husserl, the patient one, as suspicious of Heidegger as he always had been of Max Scheler's volcanic fire."

Robert J. Dostal understood the importance of Husserl to be profound:

Heidegger himself, who is supposed to have broken with Husserl, bases his hermeneutics on an account of time that not only parallels Husserl's account in many ways but seems to have been arrived at through the same phenomenological method as was used by Husserl.... The differences between Husserl and Heidegger are significant, but if we do not see how much it is the case that Husserlian phenomenology provides the framework for Heidegger's approach, we will not be able to appreciate the exact nature of Heidegger's project in Being and Time or why he let it unfinished.

Daniel O. Dahlstrom saw Heidegger's presentation of his work as a departure from Husserl as unfairly misrepresenting Husserl's own work. Dahlstrom concluded his consideration of the relation between Heidegger and Husserl as follows:

Heidegger's silence about the stark similarities between his account of temporality and Husserl's investigation of internal time - consciousness contributes to a misrepresentation of Husserl's account of intentionality. Contrary to the criticisms Heidegger advances in his lectures, intentionality (and, by implication, the meaning of 'to be') in the final analysis is not construed by Husserl as sheer presence (be it the presence of a fact or object, act or event). Yet for all its "dangerous closeness" to what Heidegger understands by temporality, Husserl's account of internal time - consciousness does differ fundamentally. In Husserl's account the structure of protentions is accorded neither the finitude nor the primacy that Heidegger claims are central to the original future of ecstatic - horizonal temporality.

Heideggerians regarded Søren Kierkegaard as, by far, the greatest philosophical contributor to Heidegger's own existentialist concepts. Heidegger's concepts of anxiety (Angst) and mortality draw on Kierkegaard and are indebted to the way in which the latter lays out the importance of our subjective relation to truth, our existence in the face of death, the temporality of existence, and the importance of passionate affirmation of one's individual being - in - the - world.

Friedrich Hölderlin and Friedrich Nietzsche were both important influences on Heidegger, and many of his lecture courses were devoted to one or the other, especially in the 1930s and 1940s. The lectures on Nietzsche focused on fragments posthumously published under the title The Will to Power, rather than on Nietzsche's published works. Heidegger read The Will to Power as the culminating expression of Western metaphysics, and the lectures are a kind of dialogue between the two thinkers.

This is also the case for the lecture courses devoted to the poetry of Friedrich Hölderlin, which became an increasingly central focus of Heidegger's work and thought. Heidegger grants to Hölderlin a singular place within the history of being and the history of Germany, as a herald whose thought is yet to be "heard" in Germany or the West. Many of Heidegger's works from the 1930s onwards include meditations on lines from Hölderlin's poetry, and several of the lecture courses are devoted to the reading of a single poem (for example, Hölderlin's Hymn "The Ister").

Some writers on Heidegger's work see possibilities within it for dialogue with traditions of thought outside of Western philosophy, particularly East Asian thinking. Despite perceived differences between Eastern and Western philosophy, some of Heidegger's later work, particularly "A Dialogue on Language between a Japanese and an Inquirer", does show an interest in initiating such a dialogue. Heidegger himself had contact with a number of leading Japanese intellectuals, including members of the Kyoto School, notably Hajime Tanabe and Kuki Shūzō. It has also been claimed that a number of elements within Heidegger's thought bear a close parallel to Eastern philosophical ideas, particularly Zen Buddhism and Taoism. Paul Hsao records Chang Chung - Yuan saying that "Heidegger is the only Western Philosopher who not only intellectually understands but has intuitively grasped Taoist thought." Some authors see great influence of Japanese scholars in Heidegger's work, although this influence is not acknowledged by the author.

Some scholars interested in the relationships between Western philosophy and the history of ideas in Islam and Arabic philosophical medieval sources may have been influenced by Heidegger's work, including recent studies by Nader El - Bizri. It is claimed the works of counter - enlightenment philosophers such as Heidegger, along with Friedrich Nietzsche and Joseph de Maistre, influenced Iran's Shia Islamists, notably Ali Shariati, in constructing the ideological foundations of the Iranian Revolution and modern political Islam.

Adolf Hitler was sworn in as Chancellor of Germany on January 30, 1933. Heidegger was elected rector of the University of Freiburg on April 21, 1933, and assumed the position the following day. On May 1 he joined the Nazi Party.

Heidegger delivered his inaugural address, the Rektoratsrede, on "Die Selbstbehauptung der Deutschen Universität" ("The Self - assertion of the German University") on May 27.

His tenure as rector was fraught with difficulties from the outset. Some National Socialist education officials viewed him as a rival, while others saw his efforts as comical. Some of Heidegger's fellow National Socialists also ridiculed his philosophical writings as gibberish. He finally offered his resignation on April 23, 1934, and it was accepted on April 27. Heidegger remained a member of both the academic faculty and of the Nazi Party until the end of the war.

Philosophical historian Hans Sluga wrote:

"Though as rector he prevented students from displaying an anti - Semitic poster at the entrance to the university and from holding a book burning, he kept in close contact with the Nazi student leaders and clearly signaled to them his sympathy with their activism."

In 1945 Heidegger wrote of his term as rector, giving the writing to his son Hermann; it was published in 1983:

"The rectorate was an attempt to see something in the movement that had come to power, beyond all its failings and crudeness, that was much more far - reaching and that could perhaps one day bring a concentration on the Germans' Western historical essence. It will in no way be denied that at the time I believed in such possibilities and for that reason renounced the actual vocation of thinking in favor of being effective in an official capacity. In no way will what was caused by my own inadequacy in office be played down. But these points of view do not capture what is essential and what moved me to accept the rectorate.""

Beginning in 1917, German - Jewish philosopher Edmund Husserl championed Heidegger's work, and helped him secure the retiring Husserl's chair in Philosophy at the University of Freiburg.

On April 6, 1933, the Reichskommissar of Baden Province, Robert Wagner, suspended all Jewish government employees, including present and retired faculty at the University of Freiburg. Heidegger's predecessor as Rector formally notified Husserl of his "enforced leave of absence" on April 14, 1933.

Heidegger became Rector of the University of Freiburg on April 22, 1933. The following week the national Reich law of April 28, 1933, replaced Reichskommissar Wagner's decree. The Reich law required the firing of Jewish professors from German universities, including those, such as Husserl, who had converted to Christianity. The termination of the retired professor Husserl's academic privileges thus did not involve any specific action on Heidegger's part.

Heidegger had by then broken off contact with Husserl, other than through intermediaries. Heidegger later claimed that his relationship with Husserl had already become strained after Husserl publicly "settled accounts" with Heidegger and Max Scheler in the early 1930s.

Heidegger did not attend his former mentor's cremation in 1938. In 1941, under pressure from publisher Max Niemeyer, Heidegger agreed to remove the dedication to Husserl from Being and Time (restored in post war editions).

Heidegger's behavior towards Husserl has evoked controversy. Hannah Arendt initially suggested that Heidegger's behavior precipitated Husserl's death. She called Heidegger a "potential murderer." However, she later recanted her accusation.

After the failure of Heidegger's rectorship, he withdrew from most political activity, without canceling his membership in the NSDAP (Nazi Party). Nevertheless, references to National Socialism continued to appear in his work.

The most controversial such reference occurred during a 1935 lecture which was published in 1953 as part of the book Introduction to Metaphysics. In the published version, Heidegger refers to the "inner truth and greatness" of the National Socialist movement (die innere Wahrheit und Größe dieser Bewegung), but he then adds a qualifying statement in parentheses: "namely, the confrontation of planetary technology and modern humanity" (nämlich die Begegnung der planetarisch bestimmten Technik und des neuzeitlichen Menschen). However, it subsequently transpired that this qualification had not been made during the original lecture, although Heidegger claimed that it had been. This has led scholars to argue that Heidegger still supported the Nazi party in 1935 but that he did not want to admit this after the war, and so he attempted to silently correct his earlier statement.

In private notes written in 1939, Heidegger took a strongly critical view of Hitler's ideology, however in public lectures he seems to have continued to make ambiguous comments which, if they expressed criticism of the regime, did so only in the context of praising its ideals. For instance, in a 1942 lecture, published posthumously, Heidegger said of recent German classics scholarship: "In the majority of 'research results,' the Greeks appear as pure National Socialists. This over - enthusiasm on the part of academics seems not even to notice that with such "results" it does National Socialism and its historical uniqueness no service at all, not that it needs this anyhow.

An important witness to Heidegger's continued allegiance to National Socialism during the post - rectorship period is his former student Karl Löwith, who met Heidegger in 1936 while Heidegger was visiting Rome. In an account set down in 1940 (though not intended for publication), Löwith recalled that Heidegger wore a swastika pin to their meeting, though Heidegger knew that Löwith was Jewish. Löwith also recalled that Heidegger "left no doubt about his faith in Hitler", and stated that his support for National Socialism was in agreement with the essence of his philosophy.

After the end of World War II, Heidegger was summoned to appear at a denazification hearing. Heidegger's former lover Hannah Arendt spoke on his behalf at this hearing, while Jaspers spoke against him. The result of the hearings was that Heidegger was forbidden to teach between 1945 and 1951. One consequence of this teaching ban was that Heidegger began to engage far more in the French philosophical scene.

In his postwar thinking, Heidegger distanced himself from Nazism, but his critical comments about Nazism seem "scandalous" to some since they tend to equate the Nazi war atrocities with other inhumane practices related to rationalization and industrialization, including the treatment of animals by factory farming. For instance in a lecture delivered at Bremen in 1949, Heidegger said: "Agriculture is now a motorized food industry, the same thing in its essence as the production of corpses in the gas chambers and the extermination camps, the same thing as blockades and the reduction of countries to famine, the same thing as the manufacture of hydrogen bombs."

In 1967 Heidegger met with the Jewish poet Paul Celan, a concentration camp survivor. Celan visited Heidegger at his country retreat and wrote an enigmatic poem about the meeting, which some interpret as Celan's wish for Heidegger to apologize for his behavior during the Nazi era.

On September 23, 1966, Heidegger was interviewed by Rudolf Augstein and Georg Wolff for Der Spiegel magazine, in which he agreed to discuss his political past provided that the interview be published posthumously (it was published on May 31, 1976). In the interview, Heidegger defended his entanglement with National Socialism in two ways: first, he argued that there was no alternative, saying that he was trying to save the university (and science in general) from being politicized and thus had to compromise with the Nazi administration. Second, he admitted that he saw an "awakening" ("Aufbruch") which might help to find a "new national and social approach," but said that he changed his mind about this in 1934, largely prompted by the violence of the Night of the Long Knives.

In his interview Heidegger defended as double - speak his 1935 lecture describing the "inner truth and greatness of this movement." He affirmed that Nazi informants who observed his lectures would understand that by "movement" he meant National Socialism. However, Heidegger asserted that his dedicated students would know this statement was no eulogy for the NSDAP. Rather, he meant it as he expressed it in the parenthetical clarification later added to Introduction to Metaphysics (1953), namely, "the confrontation of planetary technology and modern humanity."

The Löwith account from 1936 has been cited to contradict the account given in the Der Spiegel interview in two ways: that there he did not make any decisive break with National Socialism in 1934, and that Heidegger was willing to entertain more profound relations between his philosophy and political involvement. The Der Spiegel interviewers did not bring up Heidegger's 1949 quotation comparing the industrialization of agriculture to the extermination camps. In fact, the interviewers were not in possession of much of the evidence now known for Heidegger's Nazi sympathies.

Heidegger was one of the most influential philosophers of the 20th century, and his ideas have penetrated into many areas, but in France there is a very long and particular history of reading and interpreting his work.

Heidegger's influence on French philosophy began in the 1930s, when Being and Time, "What is Metaphysics?" and other Heideggerian texts were read by Jean - Paul Sartre and other existentialists, as well as by thinkers such as Emmanuel Levinas, Alexandre Kojève and Georges Bataille. Because Heidegger's discussion of ontology (the study of being) is rooted in an analysis of the mode of existence of individual human beings (Da-sein, or there - being), his work has often been associated with existentialism. The influence of Heidegger on Sartre's Being and Nothingness is marked, but Heidegger felt that Sartre had misread his work, as he argued in later texts such as the "Letter on 'Humanism'." In that text, intended for a French audience, Heidegger explained this misreading in the following terms:

Sartre's key proposition about the priority of existentia over essentia [that is, Sartre's statement that "existence precedes essence"] does, however, justify using the name "existentialism" as an appropriate title for a philosophy of this sort. But the basic tenet of "existentialism" has nothing at all in common with the statement from Being and Time [that "the 'essence' of Dasein lies in its existence"] — apart from the fact that in Being and Time no statement about the relation of essentia and existentia can yet be expressed, since there it is still a question of preparing something precursory.

"Letter on 'Humanism'" is often seen as a direct response to Sartre's 1945 lecture "Existentialism is a Humanism." Aside from merely disputing readings of his own work, however, in "Letter on 'Humanism,'" Heidegger asserts that "Every humanism is either grounded in a metaphysics or is itself made to be the ground of one." Heidegger's largest issue with Sartre's existential humanism is that, while it does make a humanistic 'move' in privileging existence over essence, "the reversal of a metaphysical statement remains a metaphysical statement." From this point onward in his thought, Heidegger attempted to think beyond metaphysics to a place where the articulation of the fundamental questions of ontology were fundamentally possible: only from this point can we restore (that is, re-give [redonner]) any possible meaning to the word "humanism".

After the war, Heidegger was banned from university teaching for a period on account of his activities as Rector of Freiburg University. He developed a number of contacts in France, where his work continued to be taught, and a number of French students visited him at Todtnauberg (see, for example, Jean - François Lyotard's brief account in Heidegger and "the Jews", which discusses a Franco - German conference held in Freiburg in 1947, one step toward bringing together French and German students). Heidegger subsequently made several visits to France, and made efforts to keep abreast of developments in French philosophy by way of correspondence with Jean Beaufret, an early French translator of Heidegger, and with Lucien Braun.

Deconstruction came to Heidegger's attention in 1967 by way of Lucien Braun's recommendation of Jacques Derrida's work (Hans - Georg Gadamer was present at an initial discussion and indicated to Heidegger that Derrida's work came to his attention by way of an assistant). Heidegger expressed interest in meeting Derrida personally after the latter sent him some of his work. There was discussion of a meeting in 1972, but this failed to take place. Heidegger's interest in Derrida is said by Braun to have been considerable (as is evident in two letters, of September 29, 1967 and May 16, 1972, from Heidegger to Braun). Braun also brought to Heidegger's attention the work of Michel Foucault. Foucault's relation to Heidegger is a matter of considerable difficulty; Foucault acknowledged Heidegger as a philosopher whom he read but never wrote about. (For more on this see Penser à Strasbourg, Jacques Derrida, et al., which includes reproductions of both letters and an account by Braun, "À mi - chemin entre Heidegger et Derrida").

Jacques Derrida made emphatic efforts to displace the understanding of Heidegger's work that had been prevalent in France from the period of the ban against Heidegger teaching in German universities, which amounted to an almost wholesale rejection of the influence of Jean - Paul Sartre and existentialist terms. In Derrida's view, deconstruction is a tradition inherited via Heidegger (the French term "déconstruction" is a term coined to translate Heidegger's use of the words "Destruktion" — literally "destruction" — and "Abbau" — more literally "de-building"). According to Derrida, Sartre's interpretation of Dasein and other key Heideggerian concerns is overly psychologistic, anthropocentric, and misses the historicality central to Dasein in Being and Time. Because of Derrida's vehement attempts to "rescue" Heidegger from his existentialist interpreters (and also from Heidegger's "orthodox" followers), Derrida has at times been represented as a "French Heidegger", to the extent that he, his colleagues, and his former students are made to go proxy for Heidegger's worst (political) mistakes, despite ample evidence that the reception of Heidegger's work by later practitioners of deconstruction is anything but doctrinaire.

Derrida, Lacoue - Labarthe, and Jean - François Lyotard, among others, all engaged in debate and disagreement about the relation between Heidegger's philosophy and his Nazi politics. These debates included the question of whether it was possible to do without Heidegger's philosophy, a position which Derrida in particular rejected. Forums where these debates took place include the proceedings of the first conference dedicated to Derrida's work, published as "Les Fins de l'homme à partir du travail de Jacques Derrida: colloque de Cerisy, 23 juillet - 2 août 1980", Derrida's "Feu la cendre / cio' che resta del fuoco", and the studies on Paul Celan by Lacoue - Labarthe and Derrida which shortly preceded the detailed studies of Heidegger's politics published in and after 1987.

When in 1987 Víctor Farías published his book Heidegger et le nazisme, this debate was taken up by many others, some of whom were inclined to disparage so-called "deconstructionists" for their association with Heidegger's philosophy. Derrida and others not only continued to defend the importance of reading Heidegger, but attacked Farías on the grounds of poor scholarship and for what they saw as the sensationalism of his approach. Not all scholars agreed with this negative assessment: Richard Rorty, for example, declared that "[Farias'] book includes more concrete information relevant to Heidegger's relations with the Nazis than anything else available, and it is an excellent antidote to the evasive apologetics that are still being published."

More recently, Heidegger's thought has considerably influenced the work of the French philosopher Bernard Stiegler. This is evident even from the title of Stiegler's multi - volume magnum opus, La technique et le temps (volume one translated into English as Technics and Time, 1: The Fault of Epimetheus). Stiegler offers an original reading of Heidegger, arguing that there can be no access to "originary temporality" other than via material, that is, technical, supports, and that Heidegger recognized this in the form of his account of world historicality, yet in the end suppressed that fact. Stiegler understands the existential analytic of Being and Time as an account of psychic individuation, and his later "history of being" as an account of collective individuation. He understands many of the problems of Heidegger's philosophy and politics as the consequence of Heidegger's inability to integrate the two.

Heidegger has been very influential on the work of Italian philosopher Giorgio Agamben. Agamben attended seminars in France led by Heidegger in the late 1960s.

Heidegger's influence upon 20th century continental philosophy is unquestioned and has produced a variety of critical responses.

The content of Being and Time, according to Husserl, claimed to deal with ontology, but from Husserl's perspective only did so in the first few pages of the book. Having nothing further to contribute to an ontology independent of human existence, Heidegger changed the topic to Dasein. Whereas Heidegger argued that the question of human existence is central to the pursuit of the question of being, Husserl criticized this as reducing phenomenology to "philosophical anthropology" and offering an abstract and incorrect portrait of the human being.

The Neo - Kantian Ernst Cassirer and Heidegger engaged in an influential debate located in Davos in 1929, concerning the significance of Kantian notions of freedom and rationality. Whereas Cassirer defended the role of rationality in Kant, Heidegger argued for the priority of the imagination. Dilthey's student Georg Misch wrote the first extended critical appropriation of Heidegger in Lebensphilosophie und Phänomenologie. Eine Auseinandersetzung der Diltheyschen Richtung mit Heidegger und Husserl, Leipzig 1930 (3. ed. Stuttgart 1964).

Hegel - influenced Marxist thinkers, especially György Lukács and the Frankfurt School, associated the style and content of Heidegger's thought with German irrationalism and criticized its political implications.

Initially members of the Frankfurt School were positively disposed to Heidegger, becoming more critical at the beginning of the 1930s. Heidegger's student Herbert Marcuse became associated with the Frankfurt School. Initially striving for a synthesis between Hegelian - Marxism and Heidegger's phenomenology, Marcuse later rejected Heidegger's thought for its "false concreteness" and "revolutionary conservativism." Theodor Adorno wrote an extended critique of the ideological character of Heidegger's early and later use of language in the Jargon of Authenticity. Contemporary social theorists associated with the Frankfurt School have remained largely critical of Heidegger's works and influence. In particular, Jürgen Habermas admonishes the influence of Heidegger on recent French philosophy in his polemic against "postmodernism" in The Philosophical Discourse of Modernity (1985). However, recent work by philosopher and critical theorist Nikolas Kompridis tries to show that Heidegger's insights into world disclosure are badly misunderstood and mishandled by Habermas, and are of vital importance for critical theory, offering an important way of renewing that tradition.

Criticism of Heidegger's philosophy has also come from analytic philosophy, beginning with logical positivism. In "The Elimination of Metaphysics Through Logical Analysis of Language" (1932), Rudolf Carnap accused Heidegger of offering an "illusory" ontology, criticizing him for committing the fallacy of reification and for wrongly dismissing the logical treatment of language which, according to Carnap, can only lead to writing "nonsensical pseudo - propositions."

A strong critic of Heidegger's philosophy was the British logical positivist A.J. Ayer. In Ayer's view, Heidegger proposed vast, overarching theories regarding existence, which are completely unverifiable through empirical demonstration and logical analysis. For Ayer, this sort of philosophy was a poisonous strain in modern thought. He considered Heidegger to be the worst example of such philosophy, which Ayer believed to be entirely useless.

Bertrand Russell commented, expressing the sentiments of many mid 20th century analytic philosophers, that:

Highly eccentric in its terminology, his philosophy is extremely obscure. One cannot help suspecting that language is here running riot. An interesting point in his speculations is the insistence that nothingness is something positive. As with much else in Existentialism, this is a psychological observation made to pass for logic.

Roger Scruton stated that: "His major work Being and Time is formidably difficult — unless it is utter nonsense, in which case it is laughably easy. I am not sure how to judge it, and have read no commentator who even begins to make sense of it".

The analytic tradition values clarity of expression. Heidegger, however, has on occasion appeared to take an opposing view, stating for example that "those in the crossing must in the end know what is mistaken by all urging for intelligibility: that every thinking of being, all philosophy, can never be confirmed by 'facts,' i.e., by beings. Making itself intelligible is suicide for philosophy. Those who idolize 'facts' never notice that their idols only shine in a borrowed light. They are also meant not to notice this; for thereupon they would have to be at a loss and therefore useless. But idolizers and idols are used wherever gods are in flight and so announce their nearness." Apart from the charge of obscurantism, other analytic philosophers considered the actual content of Heidegger's work to be either faulty and meaningless, vapid or uninteresting.

Not all analytic philosophers, however, have been as hostile. Gilbert Ryle wrote a critical yet positive review of Being and Time. Ludwig Wittgenstein made a remark recorded by Friedrich Waismann: "To be sure, I can imagine what Heidegger means by being and anxiety" which has been construed by some commentators as sympathetic to Heidegger's philosophical approach. These positive and negative analytic evaluations have been collected in Michael Murray (ed.), Heidegger and Modern Philosophy: Critical Essays (Yale University Press, 1978). Heidegger's reputation within English language philosophy has slightly improved in philosophical terms in some part through the efforts of Hubert Dreyfus, Richard Rorty, and a recent generation of analytically oriented phenomenology scholars. Pragmatist Rorty claimed that Heidegger's approach to philosophy in the first half of his career has much in common with that of the latter - day Ludwig Wittgenstein, a significant figure in analytic philosophy. Nevertheless, Rorty asserted that what Heidegger had constructed in his writings was a myth of being rather than an account of it.

Even though Heidegger is considered by many observers to be the most influential philosopher of the 20th century in continental philosophy, aspects of his work have been criticized by those who nevertheless acknowledge this influence, such as Hans - Georg Gadamer and Jacques Derrida. Some questions raised about Heidegger's philosophy include the priority of ontology, the status of animals, the nature of the religious, Heidegger's supposed neglect of ethics (Emmanuel Levinas), the body (Maurice Merleau - Ponty), or sexual difference (Luce Irigaray).

Emmanuel Levinas was deeply influenced by Heidegger yet became one of his fiercest critics, contrasting the infinity of the good beyond being with the immanence and totality of ontology. Levinas also condemned Heidegger's involvement with National Socialism, stating "One can forgive many Germans, but there are some Germans it is difficult to forgive. It is difficult to forgive Heidegger."