Gilles Deleuze (January 18, 1925–November 4, 1995) was one of the most influential and prolific French philosophers of the second half of the twentieth century. Deleuze conceived of philosophy as the production of concepts, and he characterized himself as a “pure metaphysician.” In his magnum opus Difference and Repetition, he tries to develop a metaphysics adequate to contemporary mathematics and science—a metaphysics in which the concept of multiplicity replaces that of substance, event replaces essence and virtuality replaces possibility. Deleuze also produced studies in the history of philosophy (on Hume, Nietzsche, Kant, Bergson, Spinoza, Foucault, and Leibniz), and on the arts (a two- volume study of the cinema, books on Proust and Sacher-Masoch, a work on the painter Francis Bacon, and a collection of essays on literature.) Deleuze considered these latter works as pure philosophy, and not criticism, since he sought to create the concepts that correspond to the artistic practices of painters, filmmakers, and writers. In 1968, he met Félix Guattari, a political activist and radical psychoanalyst, with whom he wrote several works, among them the two-volume Capitalism and Schizophrenia, comprised of Anti-Oedipus (1972) and A Thousand Plateaus (1980). Their final collaboration was What is Philosophy? (1991).

Deleuze is noteworthy for his rejection of the Heideggerian notion of the “end of metaphysics.” In an interview, he once offered this self-assessment: “I feel myself to be a pure metaphysician.... Bergson says that modern science hasn't found its metaphysics, the metaphysics it would need. It is this metaphysics that interests me.” [Villani 1999: 130.]) We should also point to the extent of his non-philosophical references (inter alia, differential calculus, thermodynamics, geology, molecular biology, population genetics, ethology, embryology, anthropology, psychoanalysis, economics, linguistics, and even esoteric thought); his colleague Jean-François Lyotard spoke of him as a “library of Babel.” Although it remains to be seen whether the 20th century will be “Deleuzean,” as his friend Michel Foucault once quipped, Deleuze's influence reaches beyond philosophy; his work is approvingly cited by, and his concepts put to use by, researchers in architecture, urban studies, geography, film studies, musicology, anthropology, gender studies, literary studies and other fields.

One of the barriers to Deleuze's being better read among mainstream philosophers is the difficulty of his writing style in his original works (as opposed to his historical works, which are often models of clarity and concision). Deleuze's prose can be highly allusive, as well as peppered with neologisms; to make matters even more complex, these terminological innovations shift from one work to the other. While claims of intentional obscurantism are not warranted, Deleuze did mean for his style to keep readers on their toes, or even to “force” them to rethink their philosophical assumptions.

His work has typically been divided into three periods:

• 1950s-1960s: Deleuze began his career by writing traditional monographs on various classic figures in the history of philosophy, including Hume (1953), Nietzsche (1962), Kant (1963), Bergson (1966), and Spinoza (1968). After this philosophical apprenticeship in the history of philosophy, Deleuze published his magnum opus, Difference and Repetition (1968) a work in metaphysics and ontology, followed by a treatise on logic entitled Logic of Sense (1969)

• 1970s: His second period was marked by his collaboration with Félix Guattari, with whom he wrote a two volume work of political philosophy entitled Capitalism and Schizophrenia (1972; 1980), the first volume of which was written in the wake of the events of May 1968, and is often read as a philosophical reaction to it.

• 1980s-1990s: Deleuze’s last works initially focused on questions of aesthetics, and included books on painting (Francis Bacon: The Logic of Sensation, 1981), the cinema (The Movement-Image, 1983; The Time Image, 1985), the Baroque (Leibniz and the Baroque, 1988), and literature (Essays Critical and Clinical, 1993). He ended his career with a culminating reflection on the nature of philosophy entitled, simply, What is Philosophy? (1991).

Many of these works have since become classics in their respective fields. Nietzsche and Philosophy (1962) has long been recognized as one of the landmark interpretations of Nietzsche, and Difference and Repetition (1968) is one of the seminal works of twentieth-century European metaphysics. Given the diverse directions of his thought, Deleuze has had a wide-ranging impact, not only on philosophy, but also on numerous fields in the humanities, including not art history, film studies, and literary theory, among others. He remains one of the most cited authors in the humanities, and the secondary literature on his writings is already immense, and growing rapidly. Even during his lifetime, Deleuze’s significance was recognized by his peers. “I consider him to be the greatest living French philosopher,” Michel Foucault declared in 1978, even going so far as to predict, in an oft-cited remark, that “perhaps, one day, this century will be called ‘the Deleuzian century.’”

Within the French philosophical field, Deleuze nonetheless occupies a somewhat singular position, since the terms most frequently used to describe the various strains of European thought (phenomenology, hermeneutics, structuralism, postmodernism, etc.) are largely inapplicable to his work. Unlike his compatriot Jacques Derrida, Deleuze never engaged in the “deconstruction” of texts or word play. Indeed, Deleuze conceived of philosophy as the creation of concepts, and his writings take the form of precise deductions of concepts. For this reason, Deleuze’s work often transcended the divide, in the discipline of philosophy, between the so-called “continental” (European) and “analytic” (Anglo- American) traditions. His monographs in the history of philosophy, in particular, are recognized in analytic philosophy for the clarity and rigor (and originality) of their analyses. In France, many of them have become required reading for the agrégation exam in philosophy, which allows one to teach within the French university system—a sign that his writings have achieved a certain canonical status within the discipline.