Virtually every area of humanistic scholarship and artistic activity in the latter part of the 20th century felt the influence of the French philosopher Jacques Derrida, who has died aged 74 from pancreatic cancer.

"Deconstruction", the word he transformed from a rare French term to a common _expression in many languages, became part of the vocabulary not only of philosophers and literary theorists but also of architects, theologians, artists, political theorists, educationists, music critics, filmmakers, lawyers and historians. Resistance to his thinking, too, was widespread and sometimes bitter, as it challenged academic norms and, sometimes, common sense.

Derrida's name has probably been mentioned more frequently in books, journals, lectures, and common-room conversations during the last 30 years than that of any other living thinker. He was the subject of films, cartoons and at least one rock song, by Scritti Politi; he generated both adulatory and vituperative journalism; and he wrote some of the most formidably difficult philosophical works of his time. If he is remembered in future centuries, it is likely to be for contributions to our understanding of language, meaning, identity, ethical decisions and aesthetic values.

Derrida's starting point was his rejection of a common model of knowledge and language, according to which understanding something requires acquaintance with its meaning, ideally a kind of acquaintance in which this meaning is directly present to consciousness. For him, this model involved "the myth of presence", the supposition that we gain our best understanding of something when it - and it alone - is present to consciousness.

He argued that understanding something requires a grasp of the ways in which it relates to other things, and a capacity to recognise it on other occasions and in different contexts - which can never be exhaustively predicted. He coined the term "differance" ( différance in French, combining the meanings of difference and deferral) to characterise these aspects of understanding, and proposed that differance is the ur-phenomenon lying at the heart of language and thought, at work in all meaningful activities in a necessarily elusive and provisional way.

The demonstration that this is so largely constituted the work of deconstruction, in which writers who laid claim to purity or transparency or universality - and this would include most of the significant figures in the philosophical tradition - could be shown, by close and careful reading, to be undoing those very claims in the act of making them by their implicit recognition of the ongoing work of differance.

For example, in an early work on the German phenomenologist Edmund Husserl, La voix et le phénomène (Speech And Phenomena, 1967), Derrida argued that the philosophical emphasis on the "living present" concealed a dependence on the idea of death: I cannot use a sign - a word or a sentence, say - without implying that it pre-exists me and will outlive me. "I am" means "I am mortal."

These readings were not done in a spirit of one-upmanship or negative criticism; Derrida claimed to love everything he deconstructed. For him, it was a mark of the greatness of Plato, Rousseau, Hegel or the Jewish philosopher Emmanuel Levinas that their texts moved beyond what they straightforwardly asserted. This affirmative attitude became particularly visible when he was discussing literary works, where he often found vivid enactments of his arguments.

Derrida moved easily among French, English and German writers, and his favourites included James Joyce, Samuel Beckett, Stéphane Mallarmé and Paul Celan. Although his name is often coupled with the term "postmodernism" (sometimes with a suggestion of moral relativism), his allegiance was much more to the strenuous aesthetic experiments of the modernist writers. For him, the fact that moral values cannot be expressed as simple rules of conduct increased, rather than decreased, the importance of our ethical responsibilities.

The warmest reception of his work occurred in university literature departments, where it was frequently studied alongside the writing of other poststructuralists, notably Michel Foucault, Jacques Lacan, Roland Barthes and Hélène Cixous.

Derrida's style was as upsetting to traditional philosophers as were his arguments. This was an important element of his famous debate in the 1970s with the American philosopher John Searle concerning the significance of JL Austin's speech-act theory, which attempted to distinguish between different kinds of utterance. While praising Austin, Derrida criticised him for giving too much priority to "serious" uses of language, and not recognising the importance of the ways in which the same speech-acts are used in humour, play-acting, teaching, citation and on other "non-serious" occasions.

Searle criticised Derrida for misrepresenting Austin (which in some respects he did), but the American, not appreciating the function of Derrida's playful style, equally misrepresented the Frenchman, who responded by writing an even more outrageous rejoinder. What might have been a valuable dialogue between Derrida and analytical philosophy of language led nowhere.

In fact, Derrida had several styles, ranging from the technical analysis of Greek terminology, through highly personal meditations to an exuberant sporting with language. He could be a highly comic writer - and an equally comic speaker, with an impeccable sense of timing - even when the issues were of the utmost gravity. This affront to convention was not born of a desire to shock; it was part of a strategy of undermining the categories - including the distinction between the serious and the non-serious - that had long dominated philosophical language. (Exceptions, such as Nietzsche, were given due credit.) Derrida's writing is strange and difficult because it has to be: to test the limits of what can be thought is to test the limits of what can be articulated.

Imitations of the Derridean style seldom succeed, and it is not surprising that a caricature version of Derrida emerged. But this flamboyantly self-regarding figure, dismissing the search for truth, declaring historical knowledge to be impossible, denying that there is anything beyond language - and doing all this in a relentless series of puns and neologisms - bore no resemblance to the person himself. He was a cautious thinker, frequently pointing out the unavoidable simplifications in what he was saying; he always insisted on philosophical and linguistic rigour (even if his understanding of what constituted rigour differed from the traditional one); and he respected truth and historical accuracy in a very traditional manner.

He was a man of remarkable modesty and generosity, quite without self-importance. Anyone who attended one of the many conferences dedicated to his work observed how conscientiously he listened to every paper (whether by a famous thinker or a graduate student), took careful notes, and asked polite but searching questions. Unknown academics sending manuscripts would receive handwritten (which sometimes meant virtually undecipherable) comments in response, always written in a positive spirit.

Jackie Derrida - he later adopted a more "correct" French version of his first name - was born in El-Biar, near Algiers, into an indigenous Jewish family. He attended local primary schools and, in 1941, entered the nearby lycée, already subject to anti-semitic Vichy laws. The following year, he was expelled as a Jew, and was not able to recommence regular schooling until 1944. Even then, he did not settle down; he dreamed of being a professional footballer and failed the baccalauréat in 1947. These were years of intense reading, however, including Rousseau, Nietzsche and Paul Valéry.

Moving through two more lycées in Algiers, Derrida was introduced to the two great precursors in 20th-century French philosophy, with whom, oddly perhaps, he never engaged at any length in print, Bergson and Sartre; he was more taken by his discovery of Kierkegaard and Heidegger. He passed the bac in 1948 and set his sights, thanks to a chance radio programme, on the École Normale Supérieure, the leading French institute for literature and philosophy.

The route lay via two years of preparatory classes at the Lycée Louis-le-grand in Paris, although it took Derrida longer than this as he suffered physically and psychologically in the new environment (it was the first time he had been out of Algeria). At his third attempt, in 1952, he was admitted to the École Normale, where, after faltering again, he finally passed the agrégation in 1956. He also made some important friends, including Louis Althusser, Foucault and the psychoanalyst Marguerite Aucouturier, whom he married in 1957.

After a year's visit to Harvard University and a spell of military service, Derrida took his first teaching job, at a lycée in Le Mans. He then taught at the Sorbonne for four years, before moving to the position he was to occupy until 1984: mitre-assistant at the École Normale. There, his seminars - written every year on a fresh topic - became Parisian institutions. His first publication (1962) was a very long introduction to his translation of a short essay by Husserl on The Origin Of Geometry. It is striking that, despite the mathematical subject-matter of this work, Derrida confidently set out in it many of the themes that were to recur later, including his conception of differance.

The event that projected him into the international limelight was a conference at Johns Hopkins University in Baltimore in 1966, where the relatively unknown (but incontrovertibly glamorous) young philosopher upstaged the likes of Lacan and Jean Hyppolite. This was to be the start of a long relationship with English departments in the US, where he was made more welcome than anywhere else in the world. (The French academic establishment never took him to its heart, and academic philosophers everywhere were generally uncomprehending.)

Derrida's annus mirabilis was 1967, which saw the publication of three extraordinary books. For philosophers, it is in La voix et le phénomène that Derrida makes, or fails to make, his case, arguing through a careful critical reading of another text by Husserl, for the fundamental role of differance in language and thought.

In L'Ecriture et la différence (Writing And Difference), he brought together essays in which he began to develop his position in the context of debates about psychoanalysis, the human sciences and ethics. But it was De la grammatologie (Of Grammatology) that created the greatest stir. After an introductory discussion in which he argued that "grammatology", the theory of written signs, can point the way to an understanding of language freed from the myth of presence and open to the work of differance, he entered upon a brilliant deconstruction of the accounts of language given by Saussure, Lévi-Strauss, Rousseau and others.

Derrida gives most attention to Rousseau, and connects the priority Rousseau gives to speech over writing with the priority he gives to nature over culture, to melody over harmony, and to coitus over masturbation. Derrida noted that, in each case, Rousseau uses the word "supplement" to designate the relationship between the second term and the first. The word suggests that the second term is inessential, merely adding to the first term, which is primary, full, self-sufficient.

Yet a secondary meaning of the word "supplement" seemed to Derrida to be playing around all Rousseau's uses of it: as the supplement to a dictionary supplies its missing terms, so writing, culture, harmony and masturbation all make up for deficiencies in what was supposed to be the perfect and complete entity to which they are in an ancillary relation.

The second entity, not quite under the author's control, comes to set the terms which make possible the first entity. "Supplementarity", thus understood, is a manifestation of differance; and other manifestations are explored in Derrida's discussions of the Greek terms pharmakon (both medicine and poison) and hymen (both separation and marriage) in his next major work La Dissémination (Dissemination, 1972).

Although Derrida was active in the protests of 1968, he had reservations about the allegiance to the Communist party of many of his associates. In 1974, he founded the Groupe De Recherche Sur L'enseignement Philoso- phique, dedicated to improving the teaching of philosophy in schools. By now, he was receiving invitations from many institutions, and important friendships were established on these travels. The American connection blossomed in the 1970s, when he began an annual visit to Johns Hopkins and then to Yale, where he worked closely with J Hillis Miller and Paul de Man (the kernel of what came to be known as the Yale school of deconstruction).

In 1980, Derrida defended a doctoral thesis at the Sorbonne, based on his publications, and, that same year, he was the focus of a 10-day Cerisy-la-Salle conference organised by two friends whose work was to remain in close touch with his, Jean-Luc Nancy and Philippe Lacoue-Labarthe. The following year, there took place an event that was to haunt him for the rest of his life: returning from a clandestine seminar in Prague, he was arrested on false drugs charges and imprisoned. His release was secured after a protest by the French government.

In order to encourage developments in philosophy outside the traditional canons, Derrida contributed to the establishment of the Collège International de Philosophie, of which he became the first director in 1983. That same year, he also participated in the creation of an anti-apartheid foundation and a writers' committee for Nelson Mandela. In 1984, he was elected to the École des Hautes Études en Sciences Sociales as director of studies. As at the École Normale, he gave an annual seminar, keeping it up after retirement in 1998, although with fewer sessions.

His friend Hillis Miller moved from Yale to the University of Irvine, California, in 1986, and Derrida switched allegiance at the same time, beginning an annual spring visitthat continued until 2003. He also began a regular short autumn visit to New York, as the guest of New York University, the New School and the Cardozo School of Law.

The discovery, in 1987, of his friend de Man's collaborationist wartime journalism was a personal blow to Derrida. At the Alabama University conference at which the articles were made public, he gave an extraordinarily moving speech expressing the complex emotions provoked by the disclosure. Around the same time, more evidence about Heidegger's involvement with the Nazi party emerged, and Derrida was obliged to make it clear that, although he owed more to Heidegger than to any other philosopher, his adherence was far from uncritical.

Derrida's honorary Cambridge degree, awarded in 1992, provoked a fierce debate and an outbreak of caricaturing, as well as spirited defences. In the early part of his career, he did not allow photographs of himself to be published, but such a simplistic opposition between the public and the private could not survive his philosophical scrutiny, and soon his image became familiar. The 2002 film Jacques Derrida, by Amy Ziering Kofman, entertainingly explored this questionable opposition, and gave a wider glimpse of its subject's wicked sense of humour.

D errida published some 70 books and countless articles. The most important volumes include Glas (1974), which staged a confrontation between Hegel and Genet by means of an ingenious page-layout; La vérité en peinture (The Truth In Painting, 1978), on visual art and attempts to theorise about it; La carte postale (The Post Card, 1987), an exploration of psychoanalytic themes through a fictional series of postcards to an unidentified addressee; and two large-scale collections of essays, Psyché: inventions de l'autre (1987), on a wide range of topics, and Du droit à la philosophie (1990), in which the institutional situation of philosophy is addressed.

In 1993 Derrida's longstanding admiration for Marx was given full elaboration in a controversial study, Spectres de Marx (Spectres Of Marx). Always a man of the left, he felt able to write this book only when Soviet communism had collapsed, as his espousal of Marx was then, he said, less likely to be misunderstood.

Derrida's later writings were increasingly concerned with ethical and political issues, including religion (both Judaism and Christianity), the question of capital punishment (to which he was vigorously opposed), and the place of animals in the tradition of western philosophy.

He and Marguerite continued to live happily in an unpretentious house in an unremarkable Parisian suburb. But he was a man with many anxieties, and death was a constant preoccupation, both philosophically and personally. Over the years, he delivered a series of moving eulogies, a collection of which was published in 2001 as The Work Of Mourning, but whose French title is even more apt: Chaque fois unique, la fin du monde (Each time unique, the end of the world).

He is survived by his wife and their sons Pierre and Jean, and a son, Daniel, by the philosopher Sylviane Agacinski.

Jacques (Jackie) Derrida, philosopher, born July 15 1930; died October 8 2004