Deleuze's works fall into two groups: on one hand, monographs interpreting the work of other philosophers (Spinoza, Leibniz, Hume, Kant, Nietzsche, Bergson, Foucault) and artists (Proust, Kafka, Francis Bacon); on the other, eclectic philosophical tomes organized by concept (e.g., difference, sense, events, schizophrenia, cinema, philosophy). Regardless of topic, however, Deleuze consistently develops variations on similar ideas.
Metaphysics
Deleuze's main philosophical project in his early works (i.e., those prior to his collaborations with Guattari) can be baldly summarized as a systematic inversion of the traditional metaphysical relationship between identity and difference. Traditionally, difference is seen as derivative from identity: e.g., to say that "X is different from Y" assumes some X and Y with at least relatively stable identities. To the contrary, Deleuze claims that all identities are effects of difference. Identities are neither logically nor metaphysically prior to difference, Deleuze argues, "given that there exist differences of nature between things of the same genus." That is, not only are no two things ever the same, the categories we use to identify individuals in the first place derive from differences. Apparent identities such as "X" are composed of endless series of differences, where "X" = "the difference between x and x'", and "x" = "the difference between...", and so forth. Difference goes all the way down. To confront reality honestly, Deleuze claims, we must grasp beings exactly as they are, and concepts of identity (forms, categories, resemblances, unities of apperception, predicates, etc.) fail to attain difference in itself. "If philosophy has a positive and direct relation to things, it is only insofar as philosophy claims to grasp the thing itself, according to what it is, in its difference from everything it is not, in other words, in its internal difference."
Like Kant and Bergson, Deleuze considers traditional notions of space and time as unifying forms imposed by the subject. Therefore he concludes that pure difference is non-spatio-temporal; it is an idea, what Deleuze calls "the virtual". (The coinage refers not to the "virtual reality" of the computer age, but to Proust's definition of what is constant in both the past and the present: "real without being actual, ideal without being abstract.") While Deleuze's virtual ideas superficially resemble Plato's forms and Kant's ideas of pure reason, they are not originals or models, nor do they transcend possible experience; instead they are the conditions of actual experience, the internal difference in itself. "The concept they [the conditions] form is identical to its object." A Deleuzean idea or concept of difference is not a wraith-like abstraction of an experienced thing, it is a real system of differential relations that creates actual spaces, times, and sensations.
Thus Deleuze, alluding to Kant and Schelling, at times refers to his philosophy as a transcendental empiricism. In Kant's transcendental idealism, experience only makes sense when organized by forms of sensibility (namely, space and time) and intellectual categories (such as causality). Assuming the content of these forms and categories to be qualities of the world as it exists independently of our perceptual access, according to Kant, spawns seductive but senseless metaphysical beliefs. (For example, extending the concept of causality beyond possible experience results in unverifiable speculation about a first cause.) Deleuze inverts the Kantian arrangement: experience exceeds our concepts by presenting novelty, and this raw experience of difference actualizes an idea, unfettered by our prior categories, forcing us to invent new ways of thinking (see below, Epistemology).
Simultaneously, Deleuze claims that being is univocal, i.e., that all of its senses are affirmed in one voice. Deleuze borrows the doctrine of ontological univocity from the medieval philosopher John Duns Scotus. In medieval disputes over the nature of God, many eminent theologians and philosophers (such as Thomas Aquinas) held that when one says that "God is good", God's goodness is only analogous to human goodness. Scotus argued to the contrary that when one says that "God is good", the goodness in question is the exact same sort of goodness that is meant when one says "Jane is good". That is, God only differs from us in degree, and properties such as goodness, power, reason, and so forth are univocally applied, regardless of whether one is talking about God, a man, or a flea.
Deleuze adapts the doctrine of univocity to claim that being is, univocally, difference. "With univocity, however, it is not the differences which are and must be: it is being which is Difference, in the sense that it is said of difference. Moreover, it is not we who are univocal in a Being which is not; it is we and our individuality which remains equivocal in and for a univocal Being." Here Deleuze at once echoes and inverts Spinoza, who maintained that everything that exists is a modification of the one substance, God or Nature. For Deleuze, there is no one substance, only an always-differentiating process, an origami cosmos, always folding, unfolding, refolding. Deleuze summarizes this ontology in the paradoxical formula "pluralism = monism".
Difference and Repetition is Deleuze's most sustained and systematic attempt to work out the details of such a metaphysics, but his other works develop similar ideas. In Nietzsche and Philosophy (1962), for example, reality is a play of forces; in Anti-Oedipus (1972), a "body without organs"; in What Is Philosophy? (1991), a "plane of immanence" or "chaosmos".
Epistemology
Deleuze's unusual metaphysics entails an equally atypical epistemology, or what he calls a transformation of "the image of thought". According to Deleuze, the traditional image of thought, found in philosophers such as Aristotle, Descartes, and Husserl, misconceives of thinking as a mostly unproblematic business. Truth may be hard to discover...it may require a life of pure theorizing, or rigorous computation, or systematic doubt...but thinking is able, at least in principle, to correctly grasp facts, forms, ideas, etc. It may be practically impossible to attain a God's-eye, neutral point of view, but that is the ideal to approximate: a disinterested pursuit that results in a determinate, fixed truth; an orderly extension of common sense. Deleuze rejects this view as papering over the metaphysical flux, instead claiming that genuine thinking is a violent confrontation with reality, an involuntary rupture of established categories. Truth changes what we think; it alters what we think is possible. By setting aside the assumption that thinking has a natural ability to recognize the truth, Deleuze says, we attain a "thought without image", a thought always determined by problems rather than solving them. "All this, however, presupposes codes or axioms which do not result by chance, but which do not have an intrinsic rationality either. It's just like theology: everything about it is quite rational if you accept sin, the immaculate conception, and the incarnation. Reason is always a region carved out of the irrational...not sheltered from the irrational at all, but traversed by it and only defined by a particular kind of relationship among irrational factors. Underneath all reason lies delirium, and drift."
Deleuze's peculiar readings of the history of philosophy stem from this unusual epistemological perspective. To read a philosopher is no longer to aim at finding a single, correct interpretation, but is instead to present a philosopher's attempt to grapple with the problematic nature of reality. "Philosophers introduce new concepts, they explain them, but they don't tell us, not completely anyway, the problems to which those concepts are a response. [...] The history of philosophy, rather than repeating what a philosopher says, has to say what he must have taken for granted, what he didn't say but is nonetheless present in what he did say." (See below, Deleuze's interpretations.)
Likewise, rather than seeing philosophy as a timeless pursuit of truth, reason, or universals, Deleuze defines philosophy as the creation of concepts. For Deleuze, concepts are not identity conditions or propositions, but metaphysical constructions that define a range of thinking, such as Plato's ideas, Descartes's cogito, or Kant's doctrine of the faculties. A philosophical concept "posits itself and its object at the same time as it is created." In Deleuze's view, then, philosophy more closely resembles practical or artistic production than it does an adjunct to a definitive scientific description of a pre-existing world (as in the tradition of Locke or Quine).
In his later work (from roughly 1981 onward), Deleuze sharply distinguishes art, philosophy, and science as three distinct disciplines, each analyzing reality in different ways. While philosophy creates concepts, the arts create novel qualitative combinations of sensation and feeling (what Deleuze calls "percepts" and "affects"), and the sciences create quantitative theories based on fixed points of reference such as the speed of light or absolute zero (which Deleuze calls "functives"). According to Deleuze, none of these disciplines enjoy primacy over the others: they are different ways of organizing the metaphysical flux, "separate melodic lines in constant interplay with one another." For example, Deleuze does not treat cinema as an art representing an external reality, but as an ontological practice that creates different ways of organizing movement and time. Philosophy, science, and art are equally, and essentially, creative and practical. Hence, instead of asking traditional questions of identity such as "is it true?" or "what is it?", Deleuze proposes that inquiries should be functional or practical: "what does it do?" or "how does it work?"
Values
In ethics and politics, Deleuze again echoes Spinoza, albeit in a sharply Nietzschean key. In a classical liberal model of society, morality begins from individuals, who bear abstract natural rights or duties set by themselves or a God. Following his rejection of any metaphysics based on identity, Deleuze criticizes the notion of an individual as an arresting or halting of differentiation (as the etymology of the word "individual" suggests). Guided by the naturalistic ethics of Spinoza and Nietzsche, Deleuze instead seeks to understand individuals and their moralities as products of the organization of pre-individual desires and powers. In the two volumes of Capitalism and Schizophrenia, Deleuze and Guattari describe history as a congealing and regimentation of "desiring-production" (a concept combining features of Freudian drives and Marxist labor) into the modern individual (typically neurotic and repressed), the nation-state (a society of continuous control), and capitalism (an anarchy domesticated into infantilizing commodification). Deleuze, following Marx, welcomes capitalism's destruction of traditional social hierarchies as liberating, but inveighs against its homogenization of all values to the aims of the market.
But how does Deleuze square his pessimistic diagnoses with his ethical naturalism? Deleuze claims that standards of value are internal or immanent: to live well is to fully express one's power, to go to the limits of one's potential, rather than to judge what exists by non-empirical, transcendent standards. Modern society still suppresses difference and alienates persons from what they can do. To affirm reality, which is a flux of change and difference, we must overturn established identities and so become all that we can become...though we cannot know what that is in advance. The pinnacle of Deleuzean practice, then, is creativity. "Herein, perhaps, lies the secret: to bring into existence and not to judge. If it is so disgusting to judge, it is not because everything is of equal value, but on the contrary because what has value can be made or distinguished only by defying judgment. What expert judgment, in art, could ever bear on the work to come?"
Deleuze's interpretations
Deleuze's studies of individual philosophers and artists are purposely heterodox. In Nietzsche and Philosophy, for example, Deleuze claims that Nietzsche's On the Genealogy of Morality is an attempt to rewrite Kant's Critique of Pure Reason, even though Nietzsche nowhere mentions the First Critique in the Genealogy, and the Genealogy's moral topics are far removed from the epistemological focus of Kant's book. Likewise, Deleuze claims that univocity is the organizing principle of Spinoza's philosophy, despite the total absence of the term from any of Spinoza's works. Deleuze once famously described his method of interpreting philosophers as "buggery (enculage)", as sneaking behind an author and producing an offspring which is recognizably his, yet also monstrous and different.
The various monographs thus are not attempts to present what Nietzsche or Spinoza strictly intended, but re-stagings of their ideas in different and unexpected ways. Rather than misinterpretation, Deleuze's peculiar readings aim to enact the creativity he believes is the acme of philosophical practice. A parallel in painting Deleuze points to is Francis Bacon's Study after Velázquez...it is quite beside the point to say that Bacon "gets Velasquez wrong". Similar considerations apply, in Deleuze's view, to his own uses of mathematical and scientific terms, pace critics such as Alan Sokal: "I'm not saying that Resnais and Prigogine, or Godard and Thom, are doing the same thing. I'm pointing out, rather, that there are remarkable similarities between scientific creators of functions and cinematic creators of images. And the same goes for philosophical concepts, since there are distinct concepts of these spaces."
Deleuze's ideas have not spawned a school, as Lacan's did. But his major collaborations with Guattari (Anti-Oedipus, A Thousand Plateaus, and What Is Philosophy?) were best-sellers in France, and his work is frequently cited in English-speaking academia (in 2007, e.g., he was the 11th most frequently cited author in English-speaking publications in the humanities, between Freud and Kant).
In the 1960s, Deleuze's portrayal of Nietzsche as a metaphysician of difference rather than a reactionary mystic contributed greatly to the plausibility of "left-wing Nietzscheanism" as an intellectual stance. His books Difference and Repetition (1968) and The Logic of Sense (1969) led Michel Foucault to declare that "one day, perhaps, this century will be called Deleuzian." (Deleuze, for his part, said Foucault's comment was "a joke meant to make people who like us laugh, and make everyone else livid.") In the 1970s, the Anti-Oedipus, written in a style by turns vulgar and esoteric, offering a sweeping analysis of the family, language, capitalism, and history via eclectic borrowings from Freud, Marx, Nietzsche, and dozens of other writers, was received as a theoretical embodiment of the anarchic spirit of May 1968. In 1994 and 1995, L'Abécédaire de Gilles Deleuze, an eight-hour series of interviews between Deleuze and Claire Parnet, aired on France's Arte Channel (a still from the program appears in the infobox above).
In the 1980s and 1990s, almost all of Deleuze's books were translated into English. Like his contemporaries Foucault, Derrida, and Lyotard, Deleuze's influence has been most strongly felt in North American humanities departments, particularly in literary theory, where Anti-Oedipus and A Thousand Plateaus are oft regarded as major statements of post-structuralism and postmodernism, though neither Deleuze nor Guattari described their work in those terms. Likewise in the English-speaking academy, Deleuze's work is typically classified as "continental philosophy".
Deleuze has attracted critics as well. The following list is not exhaustive, and gives only the briefest of summaries.
In Modern French Philosophy (1979), Vincent Descombes argues that Deleuze's account of a difference that is not derived from identity (in Nietzsche and Philosophy) is incoherent, and that his analysis of history in Anti-Oedipus is 'utter idealism', criticizing reality for falling short of a non-existent ideal of schizophrenic becoming.
In What Is Neostructuralism? (1984), Manfred Frank claims that Deleuze's theory of individuation as a process of bottomless differentiation fails to explain the unity of consciousness.
In "The Decline and Fall of French Nietzscheo-Structuralism" (1994), Pascal Engel presents a wholesale condemnation of Deleuze's thought. According to Engel, Deleuze's metaphilosophical approach makes it impossible to reasonably disagree with a philosophical system, and so destroys meaning, truth, and philosophy itself. Engel summarizes Deleuze's metaphilosophy thus: "When faced with a beautiful philosophical concept you should just sit back and admire it. You should not question it."
In The Mask of Enlightenment (1995) Stanley Rosen objects to Deleuze's interpretation of Nietzsche's eternal return.
In Deleuze: The Clamor of Being (1997), Alain Badiou claims that Deleuze's metaphysics only apparently embraces plurality and diversity, remaining at bottom relentlessly monist. Badiou further argues that, in practical matters, Deleuze's monism entails an ascetic, aristocratic fatalism akin to ancient Stoicism.
In Reconsidering Difference (1997), Todd May argues that Deleuze's claim that difference is ontologically primary ultimately contradicts his embrace of immanence, i.e., his monism. However, May believes that Deleuze can discard the primacy-of-difference thesis, and accept a Wittgensteinian holism without significantly altering his practical philosophy.
In Fashionable Nonsense (1997), Alan Sokal and Jean Bricmont accuse Deleuze of abusing mathematical and scientific terms, particularly by sliding between accepted technical meanings and his own idiosyncratic use of those terms in his philosophical system. (But see above, Deleuze's interpretations.) Deleuze's writings on subjects such as calculus and quantum mechanics are, according to Sokal and Bricmont, vague, meaningless, or unjustified. However, by Sokal and Bricmont's own admission, they suspend judgment about Deleuze's philosophical theories and terminology.
In Organs without Bodies (2003), Slavoj ?i?ek claims that Deleuze's ontology oscillates between materialism and idealism, and that the Deleuze of Anti-Oedipus ("arguably Deleuze's worst book"), the "political" Deleuze under the "'bad' influence" of Guattari, ends up, despite protestations to the contrary, as "the ideologist of late capitalism". ?i?ek also calls Deleuze to task for allegedly reducing the subject to "just another" substance and thereby failing to grasp the nothingness that, according to Lacan and ?i?ek, defines subjectivity. What remains worthwhile in Deleuze's oeuvre, ?i?ek finds, are precisely those concepts closest to ?i?ek's own ideas.
In Out of this World: Deleuze and the Philosophy of Creation (2006), Peter Hallward argues that Deleuze's insistence that being is necessarily creative and always-differentiating entails that his philosophy can offer no insight into, and is supremely indifferent to, the material, actual conditions of existence. Thus Hallward claims that Deleuze's thought is literally other-worldly, aiming only at a passive contemplation of the dissolution of all identity into the theophanic self-creation of nature.
