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Isaiah Berlin Latvian-British political philosopher and historian of ideas, one of the greatest liberal thinkers of the 20th century. Famous for the distinction between negative and positive liberty, and for his defense of value pluralism against all forms of political utopianism. Key Concepts Negative liberty: the absence of external interference — I am free when no one prevents me from acting. It is freedom from (from obstacles, coercion, interference). Berlin associates it with classical liberalism Positive liberty: the capacity for self-governance, to be one’s own master and realize one’s potential. It is freedom to (for autonomy, for self-realization). Berlin warns that it can be distorted to justify paternalism or authoritarianism Value pluralism: fundamental human values (liberty, equality, justice, fraternity) are objectively real but incommensurable — they cannot be reduced to a single hierarchy without destroying something genuine. Against all moral monism Critique of utopianism: any doctrine claiming to have found the final solution to human problems (Marxism, extreme Enlightenment rationalism) tends toward totalitarianism — the pursuit of perfection is the enemy of liberty Counter-Enlightenment: a tradition of thinkers (Vico, Hamann, Herder) who criticized the universalist reason of the Enlightenment and valued particularity, history, and culture Two concepts of liberty: seminal essay (1958) that structured the liberal-communitarian debate for decades Influenced by Locke, Hume, Mill — British liberal tradition Kant — autonomy and dignity Herder and Vico — cultural pluralism and historicity Machiavelli — incompatibility of political values Influenced John Rawls — debate on liberty and justice Communitarianism (Taylor, Walzer, MacIntyre — against Berlin) Contemporary liberalism and normative political theory Hannah Arendt — political thought Works Four Essays on Liberty (1969); Vico and Herder (1976); The Crooked Timber of Humanity (1990); The Sense of Reality (1996). ...

Jacques Derrida Algerian-French philosopher; founder of deconstruction. He subverted the Western metaphysical tradition by showing that it is structured by hierarchical binary oppositions and by the metaphysics of presence. Key Concepts Deconstruction: not destruction, but careful reading that reveals the internal tensions of a text — how the concepts that it excludes or suppresses return to destabilize it Metaphysics of presence: Western philosophy privileges presence, speech, origin, identity — Derrida shows that all presence is mediated by difference and absence Différance (neologism): play of differ (spatial distinction) and deference (temporal deferment); meaning is never fully present — it is always postponed Supplement: the element considered “external” or “secondary” (writing in relation to speech, in Rousseau) proves to be constitutive of the “original” Text: “There is nothing outside the text” — does not mean that only books exist, but that all experience is mediated by structures of signification Pharmakon (analysis of Plato): writing is at once remedy and poison — an irreducible ambivalence that philosophy attempts, unsuccessfully, to resolve Influenced by Husserl — phenomenology (first book: Speech and Phenomena) Heidegger — destruction of metaphysics (radicalizes the Destruktion) Nietzsche — critique of metaphysics and interpretive play Ferdinand de Saussure — structural linguistics (critique) Sigmund Freud — trace, unconscious, difference Influenced Literary theory (deconstruction in the USA: Paul de Man) Postcolonial studies (Spivak, translator of Of Grammatology) Queer theory Philosophy of law (Force of Law) Works Of Grammatology (1967); Writing and Difference (1967); Speech and Phenomena (1967); Margins of Philosophy (1972); Force of Law (1994); Specters of Marx (1993). ...

Jean-Jacques Rousseau Born in Geneva in 1712 and motherless from birth, Jean-Jacques Rousseau was largely self-taught and led a wandering life before rising to prominence in Paris, where he kept company with the Encyclopedists — from whom he would later break dramatically. Recognition came in 1750, when he won the Dijon Academy’s competition with a discourse that already announced his most provocative thesis: that the arts and sciences, far from improving humanity, corrupt morals. Persecuted after the publication of Emile, condemned and forced into exile, he ended his life tormented, in 1778, leaving behind the Confessions. He is the great critic of the Enlightenment from within the Enlightenment itself. ...

Jean-Paul Sartre Philosopher, novelist, and playwright, Jean-Paul Sartre was born in Paris in 1905 and trained at the École Normale Supérieure, where he met Simone de Beauvoir, his lifelong intellectual and romantic companion. A stay in Berlin in the 1930s brought him into direct contact with the phenomenology of Husserl and Heidegger, which would become the foundation of his thought. A prisoner of war in 1940–41 and later a central figure of postwar Parisian intellectual life, he made philosophy a public and engaged activity: he founded the review Les Temps Modernes, drew close to Marxism, and, faithful to his refusal of institutional honors, declined the Nobel Prize in Literature in 1964. His death, in 1980, brought tens of thousands into the streets of Paris. ...

Jeremy Bentham Founder of Utilitarianism. English jurist and philosopher; radical social reformer. His skeleton (Auto-Icon) is displayed at University College London, in accordance with his will. Key Concepts Principle of Utility: every action should be judged by its result — the greatest happiness for the greatest number Psychological hedonism: nature has placed mankind under two sovereign masters — pleasure and pain Felicific Calculus (felicific calculus): measuring pleasures and pains by intensity, duration, certainty, propinquity, fecundity, purity, extent Panopticon: circular prison where a guard can observe all without being seen — model of social control through surveillance Reform of legislation: laws must be calculated to maximize public utility Influenced by Hume — sentiments of pleasure/pain as criterion Helvétius — social happiness as the end of legislation Locke — empiricism Influenced John Stuart Mill — disciple who qualified utilitarianism Foucault — analysis of the Panopticon in Discipline and Punish Contemporary law and politics Works Introduction to the Principles of Morals and Legislation (1789); writings on the Panopticon. ...

Johann Gottlieb Fichte First post-Kantian to overcome the thing-in-itself. Founder of German Idealism; first rector of the University of Berlin (1810). The Addresses to the German Nation (1808) made him a symbol of German cultural nationalism. Key Concepts Pure Ego as absolute principle: the Ego is not a thing, it is act — free self-positing. Esse sequitur operari: being is the product of acting First thesis: the Ego posits itself (freedom, thesis) Second thesis: the Ego opposes to itself a Not-Ego (the world as necessary obstacle to freedom) Third thesis: Ego and Not-Ego mutually limit each other (synthesis → determined reality) Doctrine of Science: system of knowledge grounded in the Ego as unconditioned condition Late phase: the Ego is manifestation of God — mysticism of the Absolute Influenced by Kant — transcendental subject; overcomes the thing-in-itself Rousseau — freedom as foundation Influenced Schelling — departs from Fichte’s subjective idealism Hegel — overcomes Fichte with the Absolute as process Marx — praxis as human self-creation Works Foundations of the Doctrine of Science (1794); The Vocation of the Scholar (1794); Addresses to the German Nation (1808). ...

Johannes Kepler Born in Weil der Stadt, Germany, in 1571, Johannes Kepler was a fascinating spirit of transition: a devout Protestant, he studied theology at Tübingen but devoted his life to astronomy, convinced that to decipher the order of the heavens was to read the mind of God. He worked as assistant to the great observer Tycho Brahe in Prague and, on inheriting his data of the highest precision — especially on Mars — had at his disposal the material that would make his discoveries possible. ...

John Dewey American philosopher, the greatest exponent of pragmatism in the 20th century. He reformulated pragmatism as instrumentalism: knowledge is an instrument for solving practical problems. A philosopher of democracy and education, he exerted monumental influence on modern pedagogy. Key Concepts Instrumentalism: ideas, theories, and concepts are instruments or tools for solving concrete problems — not mirrors of reality, but means of effective action Experience as transaction: experience is not passive reception of data, but an active transaction between organism and environment — subject and object mutually transform each other Learning by doing: education must begin with concrete experience and real problems, not with passive transmission of content Democracy as a way of life: democracy is not merely a system of government, but a cooperative way of life based on communication and participation — “a democracy is more than a form of government; it is primarily a mode of associated living” Inquiry: the scientific method generalized as a logic of problem-solving — from the problematic situation to hypothesis, experimentation, and re-establishment of equilibrium Naturalism: mind, morality, and culture are natural phenomena — rejection of all Cartesian dualisms between mind/body, subject/object, theory/practice Reconstruction in philosophy: philosophy must abandon pseudo-problems (mind vs. matter, being vs. becoming) and devote itself to real human problems — social, educational, political Influenced by Hegel — dialectical integration, but without absolute idealism William James — pragmatism, stream of consciousness Peirce — logic of inquiry Darwin — evolutionary naturalism Influenced Progressive pedagogy worldwide (New School movement) Habermas — deliberative democracy and communication Richard Rorty — neopragmatism American analytic philosophy (Quine, Davidson) Works Democracy and Education (1916); Reconstruction in Philosophy (1920); Experience and Nature (1925); The Quest for Certainty (1929); Logic: The Theory of Inquiry (1938); Experience and Education (1938). ...

John Locke John Locke was born in Wrington, England, in 1632, was educated at Oxford, and practiced medicine before becoming secretary and physician to the Earl of Shaftesbury, which brought him into the orbit of high English politics. Caught up in the struggles between Parliament and the absolutist Stuart crown, he went into exile in Holland during the reign of James II and returned only in 1689, with the Glorious Revolution, which enshrined the parliamentary order he would help to justify philosophically. He is regarded as the father of classical liberalism and one of the greatest influences on empiricism and modern political thought. ...

John Rawls American political philosopher; A Theory of Justice (1971) relaunched normative political philosophy after decades of dominance by positivism and utilitarianism. The most influential work of 20th-century political philosophy. Key Concepts Veil of ignorance (veil of ignorance): to determine principles of justice, imagine an “original position” where the parties do not know their place in society (class, race, gender, talents) — the veil ensures impartiality Original position: hypothetical contractualist thought experiment — what principles would rational agents choose behind the veil? An update of Kant and Rousseau against utilitarianism Two principles of justice: Principle of liberty: each person has an equal right to basic liberties compatible with the same liberties for all Difference principle: socioeconomic inequalities are just only if: a) connected to offices open to all and b) benefit the least advantaged members of society Lexical priority: the principle of liberty takes precedence over the difference principle — liberty is not sacrificed for economic gain Justice as fairness (Justice as Fairness): society as a system of fair cooperation among free and equal persons Political liberalism (Political Liberalism, 1993): revision — the principles of justice need not rest on a comprehensive philosophical foundation, but on “overlapping consensus” among different reasonable doctrines in a pluralistic democracy Influenced by Kant — practical reason, autonomy, categorical imperative Rousseau — social contract and general will Locke — natural rights and limited government John Stuart Mill — liberalism (but criticizes utilitarianism) Influenced The whole of contemporary political philosophy (mandatory point of reference) Robert Nozick — Anarchy, State, and Utopia (libertarian critique of Rawls) Habermas — Rawls-Habermas debate on public reason Theory of international law and global justice Works A Theory of Justice (1971); Political Liberalism (1993); The Law of Peoples (1999); Justice as Fairness: A Restatement (2001). ...

John Rogers Searle, born in Denver (Colorado) in 1932, is Professor Emeritus at the University of California, Berkeley. His contributions span philosophy of language (speech act theory), philosophy of mind (the Chinese Room argument, biological naturalism), and social ontology (the construction of institutional reality). He is one of the most widely read and debated analytic philosophers of the 20th and early 21st centuries. Key Concepts Speech Act Theory (Speech Acts, 1969): Developing J.L. Austin, Searle systematises the theory. Every speech act involves: ...

John Stuart Mill Born in London in 1806, John Stuart Mill was subjected by his father, James Mill, to an extraordinarily precocious and rigorous education — designed by Bentham’s circle to form a utilitarian thinker: he learned Greek at the age of three and devoured the classics and economics in childhood. At twenty he suffered a profound existential crisis, from which he recovered partly through Romantic poetry — an experience that led him to correct the arid utilitarianism in which he had been raised. He was also an economist, a Member of Parliament, and the intellectual companion of Harriet Taylor. He became the most influential liberal of the nineteenth century. ...

Born in Moquegua, Peru, in 1894, José Carlos Mariátegui overcame a poor childhood and fragile health — which would cost him a leg and later confine him to bed — to become, as a self-taught thinker, the most original Marxist of Latin America. A combative journalist, he spent some years in Italy, where he absorbed Marxism and the ideas of Croce and Sorel; back in Peru, he founded the influential journal Amauta and the Socialist Party. He died in 1930, at only 35, leaving a brief and dazzling body of work. ...

Joseph Maréchal was a Belgian Jesuit philosopher and psychologist, founder of Transcendental Thomism — a movement that undertook a synthesis between Thomistic metaphysics and Kant’s critical philosophy. His work marks a decisive moment in the renewal of Scholasticism in the 20th century and exerted profound influence on figures such as Karl Rahner and Bernard Lonergan. Key Concepts The Starting Point of Metaphysics (Le Point de départ de la Métaphysique, 5 notebooks, 1922–1947): His principal work. Maréchal traces the history of epistemology — from Greek philosophy through Kantianism — to ground Thomistic metaphysics in the face of Kantian critique. Notebook V (“Thomism Confronting Critical Philosophy”) is the most discussed. ...

Judith Butler American philosopher; central figure in queer theory and gender studies. Gender Trouble (1990) transformed the humanities by proposing that gender is not a fixed identity, but a performance. Key Concepts Performativity of gender: gender is not what we are (substance), but what we do — a set of repeated acts, citations of norms, gestures and discourses that produce the effect of a natural essence. There is no gender identity behind gender acts Citationality: performativity is not conscious theatrical performance — it is compulsory citation of norms that preexist the subject; the subject does not freely choose its gender (against vulgar readings) Heterosexual matrix: system of norms that prescribes sex-gender-desire as coherent and aligned; the queer and the trans are the bodies that the norm excludes to constitute itself — the “abjected” Precariousness (Frames of War, 2009): lives are not equally grievable — politics determines which lives count as lives; precarious lives (racialized, queer, migrants) are those whose mourning is denied Critique of essentialist feminism: there is no “woman” as a stable political subject prior to politics — the identity “woman” is produced by feminist politics itself; this does not invalidate feminism, but complexifies it Influenced by Simone de Beauvoir — “one is not born a woman, but becomes one” (starting point) Foucault — power, discourse, production of the subject Derrida — performativity and citationality J.L. Austin — theory of speech acts Hegel — recognition and intersubjective desire Influenced Queer theory (Eve Sedgwick, Lee Edelman) Trans studies and non-binary identities Political philosophy of precariousness Contemporary feminisms (intersectional, queer, decolonial) Works Gender Trouble (1990); Bodies That Matter (1993); The Psychic Life of Power (1997); Excitable Speech (1997); Frames of War (2009); Notes Toward a Performative Theory of Assembly (2015). ...

Jürgen Habermas Born in 1929 in Germany, and marked in his youth by the experience of Nazism and the postwar period, Jürgen Habermas became the leading name of the second generation of the Frankfurt School and one of the most influential living philosophers. An assistant to Adorno, he inherited the tradition of Critical Theory but rejected its pessimism: where Horkheimer and Adorno saw modern reason degenerate into sheer domination, Habermas sought to recover an emancipatory potential within reason itself. ...

Karl Jaspers German psychiatrist and philosopher, one of the central figures of the philosophy of existence alongside Heidegger and Kierkegaard. He moved from psychiatry (General Psychopathology, 1913) to philosophy, developing a reflection on human existence centered on boundary situations, existential communication, and transcendence. He was Hannah Arendt’s mentor at Heidelberg. After World War II, he became an influential voice on the question of German guilt and the ethical foundations of politics. ...

Karl Marx Born in Trier, in the Prussian Rhineland, in 1818, Karl Marx studied law and philosophy in Bonn and Berlin, where he drew close to the Young Hegelians. Barred from an academic career by his radical positions, he turned to journalism and, hounded by censorship, went into exile in Paris, Brussels, and finally London, where he lived through decades of poverty, sustained by his friend and collaborator Friedrich Engels and poring over the economists in the Reading Room of the British Museum. More than to interpret the world, he wanted to transform it: “the philosophers have only interpreted the world in various ways; the point, however, is to change it” (Thesis 11 on Feuerbach). ...

Karl Popper Austrian-British philosopher. Proposed falsificationism as a criterion for scientific demarcation and defended the open society against totalitarianism. Sharp critic of Marxism and historicism. Key Concepts Falsifiability (The Logic of Scientific Discovery, 1934): a scientific theory is not one that can be verified (induction — the problem of Hume), but one that can be falsified — that admits the possibility of being refuted by experiments. Psychoanalysis and Marxism are not sciences: they are immune to refutation Problem of induction (asymmetrical solution): no number of observations confirms a universal law; a single counterexample falsifies it. Science progresses through the survival of the most audacious theories under severe scrutiny Critical rationalism: reason advances through bold conjectures and rigorous refutations — not through secure inductive accumulation Evolutionary epistemology: the growth of knowledge is analogous to biological evolution — variations (conjectures) eliminated by selection (refutation) Open Society (The Open Society and Its Enemies, 1945): societies that permit criticism, reform, and peaceful change of institutions; critique of Plato, Hegel, and Marx as “enemies” — historicisms that believe in inevitable laws of history and justify authoritarianism Historicism: the belief that there are historical laws that allow us to predict the future — Popper argues it is a dangerous fallacy; the future is open Influenced by Kant — limits of knowledge and the active role of the subject Hume — problem of induction (point of departure) Einstein — science as bold, refutable conjecture Influenced Contemporary philosophy of science (Lakatos, Feyerabend — disciples and critics) Thomas Kuhn (debate on scientific progress) Contemporary political liberalism George Soros — applied the “open society” as a political and philanthropic project Works The Logic of Scientific Discovery (1934); The Poverty of Historicism (1944); The Open Society and Its Enemies (1945); Conjectures and Refutations (1963); Objective Knowledge (1972). ...

Kurt Godel Kurt Gödel is widely regarded as the greatest logician since Aristotle. Born in Brünn (now Brno, Czech Republic) on 28 April 1906, and died in Princeton on 14 January 1978, his work fundamentally transformed mathematical logic, the foundations of mathematics, and the philosophy of mind. His two Incompleteness Theorems (1931) partially dismantled David Hilbert’s formalist programme and established intrinsic limits to any sufficiently powerful axiomatic system. Key Concepts First Incompleteness Theorem (Über formal unentscheidbare Sätze der Principia Mathematica und verwandter Systeme I, 1931): Gödel proved that any consistent formal system capable of expressing elementary arithmetic necessarily contains propositions that can neither be proved nor refuted within the system itself. The proof strategy is remarkably ingenious: Gödel encoded formal syntax by means of numbers (the so-called Gödel numbering), thereby constructing a sentence that, in its own arithmetic numbering, asserts “I am not provable in this system.” If the system could prove this sentence, it would be inconsistent; since it cannot, the sentence is true yet undecidable. The theorem showed that completeness — the capacity of a formal system to decide every well-formed proposition — is incompatible with consistency, for sufficiently expressive systems. ...