What exists,
and how do we know?

Philosophical thought begins in the Upanishads, the final part of the ritual-centered Vedic scriptures. The identity of Brahman, the ultimate reality of the universe, with Atman, the true self of the individual; karma and the cycle of rebirth driven by one's actions; and liberation through realizing this truth became the basic framework of Indian philosophy.

• Upanishads ↗
• Axial Age ↗

In the trading cities of Ionia, where many cultures mixed, it was hard to treat any one mythology as absolute. Thales is considered the first to look for the origin of all things (arche) in nature rather than in the gods. The way he asked the question mattered more than his answer. It was the moment philosophy and science began together.

Thales's student Anaximander said the origin of things is not a particular substance like water but the "boundless" (apeiron), something with no definite qualities at all. It was the first appeal to an abstract principle.

Leading a community that was both philosophical and religious, Pythagoras taught that the origin of all things is number and believed in the transmigration of souls. His school, where mathematics, philosophy and mysticism intertwined, deeply influenced Plato.

Heraclitus held that the world is in constant change, and that within that change is a rational order (logos) that balances the tension of opposites.

In the Spring and Autumn period, as the order of the Zhou dynasty crumbled, Confucius said he did not create anything new but merely transmitted the ways of the ancients. He taught humaneness (ren), the social norms through which it is expressed (li), and the ideal person (junzi), someone made by self-cultivation rather than birth. Of spirits and the afterlife he said, "If you do not yet understand life, how can you understand death?" and focused on ethics in this world. His disciples compiled his sayings in the Analects.

• Confucius ↗

In direct opposition to Heraclitus, Parmenides said that change is an illusion. Since what is cannot come from what is not, coming into being and change are impossible. The senses deceive us and only reason reaches truth: it was the starting point of rationalism. The opposition between change and permanence runs through all of Western philosophy.

• Parmenides ↗

To defend his teacher Parmenides, Zeno devised paradoxes showing that motion leads to contradiction. For more than 2,000 years they shook mathematics' understanding of infinity and continuity.

Born a prince, Siddhartha Gautama left home after encountering old age, sickness and death, and attained awakening (scholars disagree widely about his dates). He taught the Four Noble Truths of suffering, its cause, its end and the path; the Middle Way between the extremes of pleasure and asceticism; and dependent origination, the idea that everything arises in dependence on other things. His teaching of no-self, which denied the eternal self of the Upanishads, reached nearly the same conclusion Hume would 2,000 years later. In the same era, Mahavira founded Jainism, which pursued non-harm to every living being to the utmost.

• The Buddha ↗
• Anatta ↗

In democratic Athens, where skill in speaking before the assembly and the courts was the key to success, the Sophists appeared, teaching rhetoric for a fee. Protagoras championed a relativism that doubted absolute truth, and the Sophists raised the important distinction between convention (nomos) and nature (physis). Their bad reputation as mere tricksters with words was given to them by Plato.

Empedocles and Democritus tried to reconcile Parmenides's permanence with Heraclitus's change: the basic elements themselves never change, but their combinations do. The four-element theory and atomism came from this.

Mozi criticized the Confucian graded love that puts family first and argued for impartial care, loving all people equally. He opposed luxury and wars of aggression, and judged actions by their beneficial consequences, which makes him a kind of utilitarian. His school once rivaled Confucianism, but it later vanished.

In the streets, Socrates asked questions such as "What is justice?" and used dialogue to expose the contradictions in people's answers. He taught that virtue is knowledge and that one should care for the soul before chasing wealth. Sentenced to death for impiety and corrupting the young, he refused a chance to escape and drank the hemlock. He never wrote a line; we know him only through Plato's dialogues.

• Socrates ↗
• Socratic method ↗

Having witnessed his teacher's unjust death, Plato founded a school in Athens. He held that the world we see with our senses is a world of changing shadows, and that beyond it lie the Forms, eternal and unchanging true reality. The allegory of the cave, the theory that learning is recollection of the Forms, the tripartite soul in which reason must govern spirit and appetite, and the philosopher-king of the Republic are his best-known ideas. Whitehead remarked that all of Western philosophy is a series of footnotes to Plato.

• Plato ↗
• Theory of forms ↗

The Tao Te Ching, attributed to Laozi, is thought to have taken shape around this time (whether Laozi existed is uncertain). It says the Tao, the source of all things, cannot be put into words, and that the best way is wu wei, acting without forcing and following the flow of nature. Like water, the soft and lowly overcome the strong in the end, and Confucian morality, being artificial, is criticized as a source of disorder.

• Tao Te Ching ↗

Plato's student and tutor to Alexander the Great, Aristotle founded his own school and systematized nearly every field of knowledge. He did not place the Forms in a separate world but held that form exists within individual things, together with matter. He left the four causes, potentiality and actuality, the syllogism, and an ethics in which happiness is a life of excellent reasoning and virtue is the mean between excess and deficiency. As in The School of Athens, where Plato points up and Aristotle points to the earth, the opposition between ideal and real recurs all the way to modern rationalism and empiricism.

• Aristotle ↗
• Nicomachean Ethics ↗

Pyrrho, who traveled as far as India with Alexander's campaign, said that for any claim the opposite claim is equally plausible, so we should suspend judgment. Peace of mind, he held, would follow.

Mencius argued that human nature contains the sprouts of goodness, pointing out that anyone who sees a child about to fall into a well feels alarm and compassion, and he went so far as to say that a ruler who fails the people may be replaced. At the same time Zhuangzi, waking from a dream of being a butterfly, asked whether he had dreamed he was a butterfly or a butterfly was dreaming it was him, and held that distinctions like big and small, right and wrong, depend only on perspective.

• Mencius ↗
• Zhuangzi (book) ↗

After Alexander, as city-states were absorbed into empires, philosophy turned to how an individual could find peace of mind in a turbulent world. Epicurus said happiness is pleasure, but by pleasure he meant not indulgence but the absence of pain in the body and anxiety in the mind. Since at death our atoms simply scatter, there is no reason to fear it.

The name comes from the painted porch (stoa) in Athens where Zeno of Citium taught. The universe is ordered by reason (logos), and humans share in that reason, so virtue is living in accordance with nature. The idea that we are troubled not by events but by our judgments about them directly influenced modern cognitive behavioral therapy, and the Stoics argued for cosmopolitanism, the view that all humans are citizens of the world.

• Stoicism ↗

Xunzi argued that human nature follows selfish desires and, left alone, leads to strife, so it must be corrected through ritual and education. Mencius versus Xunzi resembles the Western contrast of Rousseau versus Hobbes.

• Xunzi (philosopher) ↗

Xunzi's student Han Feizi pushed the idea that human nature is bad to its extreme, arguing that the state must be ruled by strict laws, rewards and punishments, and the ruler's cunning. The Qin state adopted Legalism and unified China in 221 BC. He is often compared to Machiavelli.

• Legalism (Chinese philosophy) ↗

Emperor Wu of Han established official scholars to teach the Confucian classics and made Confucianism the state ideology. For the next 2,000 years Confucianism shaped politics, education and family ethics in East Asia.

Seneca, Nero's tutor and a statesman, taught the Stoic life in the form of letters, and Epictetus, born a slave, left the teaching that we must distinguish what depends on us from what does not.

Nagarjuna founded the philosophy of emptiness, the view that all things are empty of fixed essence, and the Madhyamaka school, which rejects both extremes of existence and nonexistence. His method of using rigorous logic to expose the self-contradiction in every concept is deeply philosophical.

• Nagarjuna ↗

During wars against Germanic tribes, the Roman emperor Marcus Aurelius wrote notes in his tent to steady himself. That a slave and an emperor practiced the same philosophy shows the universality of Stoicism.

• Meditations ↗

Six schools that accepted the authority of the Vedas took systematic form: Nyaya, which developed sophisticated logic and epistemology; Samkhya, a dualism of spirit and matter; Yoga, which systematized practice; Vedanta, which interpreted the Upanishads; and others.

Plotinus taught that everything emanates like light from the ultimate source, the One, and that the soul longs to return to it. His mystical Neoplatonism had a decisive influence on Christian theology.

Asanga and Vasubandhu systematized Yogacara, the view that the world we experience is entirely a product of consciousness. It is often compared with Western idealism.

Augustine used the philosophy of Plato and Plotinus to systematize Christian theology. In the Confessions, the first autobiography of deep inner reflection, he offered an original theory of time as an extension of the mind, and answered that evil is not a substance but a lack of good. When Rome was sacked in 410, he distinguished the earthly city from the City of God in The City of God.

• Augustine of Hippo ↗

Awaiting execution for treason, Boethius wrote a book in which Philosophy appears as a woman and teaches him how to bear the whims of fortune. Strongly Stoic in character, it was one of the most widely read books of the Middle Ages.

Buddhism, which had arrived around the 1st century, became Chinese as it mixed with Daoism, and the Chan school emerged, valuing awakening that sees directly into the mind over words and scriptures. Huineng's teaching became the mainstream of East Asian Zen.

• Chan Buddhism ↗

Shankara systematized Advaita Vedanta, the nondualism holding that Brahman is the only reality and the diverse world is illusion (maya). It became the mainstream of Hindu philosophy.

Ibn Sina distinguished what a thing is (essence) from whether it actually exists (existence), and left a thought experiment: a man floating in the air with all his senses cut off would still know that he exists. It calls to mind Descartes's cogito 600 years later.

• Floating man ↗

Declaring "I believe in order to understand," Anselm argued that if God is defined as that than which nothing greater can be conceived, such a being must actually exist. Kant refuted it, and it is still debated.

• Ontological argument ↗

Al-Ghazali argued that however often we see fire burn cotton, we only see the two happen together; we never see a necessary connection by which fire burns. It is strikingly similar to Hume's critique of causation 700 years later.

Over whether universal concepts like "human" or "red" really exist, realists, who said they do, and nominalists, who said they are mere names and only individuals exist, argued for centuries. Abelard tried to find a path between them.

• Problem of universals ↗

Ibn Rushd (Averroes) defended philosophy against al-Ghazali and wrote such extensive commentaries on Aristotle that in Europe he was known simply as "the Commentator." The Jewish philosopher Maimonides harmonized Jewish faith and Aristotle in The Guide for the Perplexed.

• Averroes ↗

In response to Buddhist and Daoist metaphysics, Zhu Xi of the Song dynasty rebuilt Confucianism as a philosophy. All things consist of li, principle, and qi, material energy; human nature is li itself; and one reaches knowledge by investigating the principles of things one by one. Neo-Confucianism went on to become the state ideology of several East Asian countries.

• Zhu Xi ↗

Thomas Aquinas carried out a grand synthesis of Aristotelian philosophy and Christian theology. He divided what can be known by reason from what can be known only by revelation, and set out the "Five Ways" of proving God's existence starting from experience, along with natural law theory, the moral law knowable by reason. Natural law became a foundation of Western legal thought and the idea of human rights.

• Thomas Aquinas ↗
• Summa Theologica ↗

This principle of the thoroughgoing nominalist William of Ockham is still used today as a rule for choosing models in science and statistics. By separating faith from reason, he dismantled the medieval synthesis and opened the way to modern empiricism.

• Occam's razor ↗

Against Zhu Xi, Wang Yangming of the Ming dynasty argued that principle is in the mind and that knowing and acting are one (the School of Mind).

Through the voice of the goddess Folly, the humanist Erasmus satirized the hypocrisy of clergy and scholars. Humanism, which returned to classical texts in the original, prepared the ground for the Reformation.

Machiavelli asked not what a ruler ought to do but what is actually needed to gain and keep power. It was the starting point of modern political science, which separated politics from morality.

• The Prince ↗

Thomas More described an imaginary island without private property to criticize English society of his day. "Utopia," meaning "no place," became the word for an ideal society.

Montaigne expressed a skepticism that doubted certainty in the form of personal reflection, and created the essay as a genre.

Francis Bacon championed induction, drawing general laws from observation and experiment, and analyzed the prejudices that distort knowledge as four idols: of the tribe, the cave, the marketplace and the theater.

Seeking a foundation as certain as mathematics, Descartes doubted his senses, whether he was dreaming, even that 2 + 3 = 5. But he could not doubt the existence of the self that was doubting. The starting point of knowledge became the thinking subject rather than God or the world. His mind–body dualism, which separated mind from matter, left the problem of how mind and body interact, a problem that runs all the way to today's debates about AI and consciousness.

• René Descartes ↗
• Cogito, ergo sum ↗

Having lived through the English Civil War, Hobbes saw life in a state of nature without government as "solitary, poor, nasty, brutish, and short." So, he argued, people make a contract for security and hand their rights to a powerful sovereign: the social contract.

• Leviathan (Hobbes book) ↗

Excommunicated from the Jewish community and living by grinding lenses, Spinoza held that there is only one substance, which is both God and nature, and that mind and matter are just two aspects of it. He wrote the Ethics like Euclid's Elements, in definitions, axioms, propositions and proofs, and saw freedom as understanding necessity through reason. It was published after his death.

• Baruch Spinoza ↗

Locke rejected Descartes's innate ideas, holding that the mind is a blank slate and all ideas come from experience. The same year, in his Two Treatises of Government, he argued that people have natural rights to life, liberty and property, and may resist a government that violates them. It directly influenced the American Declaration of Independence.

• John Locke ↗

Berkeley argued that since all we directly know are sensations, we have no grounds to say that matter exists beyond them. A tree no one is looking at exists because God perceives it. He is the same Bishop Berkeley who attacked Newton's calculus as "the ghosts of departed quantities."

Leibniz held that the world consists of countless spiritual units, monads, which do not affect one another but appear to interact through a harmony pre-established by God, and he took as a principle the principle of sufficient reason: everything has a reason. His dream of a universal symbolic language that would turn all thought into calculation led toward modern logic and the computer.

Hume pushed empiricism to its limit. However many times we see billiard balls collide, we never experience the necessary connection itself, so causation is a habit formed by repetition, and nothing guarantees the sun will rise tomorrow: the problem of induction. Looking inward, he found only a stream of perceptions, so the self is a bundle of perceptions (almost the same conclusion as the Buddha's no-self), and he pointed out that you cannot derive an "ought" from an "is."

• David Hume ↗
• Problem of induction ↗

Montesquieu proposed the separation of powers, dividing power into legislative, executive and judicial branches that check one another. It became a basic principle of modern constitutions.

Diderot and d'Alembert began publishing the Encyclopédie, which set out to organize all knowledge of science, technology and the arts. Despite censorship and bans, it continued for more than 20 years and spread Enlightenment ideas. In 1759 Voltaire's Candide savagely satirized Leibniz's "best of all possible worlds."

Rousseau, the Enlightenment's maverick, held that civilization had corrupted humanity and that people in the state of nature were good (the opposite of Hobbes). He argued for a state guided by the general will, aiming at the common good rather than the sum of private interests, and deeply influenced the French Revolution.

• The Social Contract ↗

Kant, who said reading Hume woke him from his "dogmatic slumber," turned the perspective around. Time and space are the forms through which we receive objects, and concepts like causation are frameworks our understanding uses to organize experience. So causation is not a habit; it necessarily applies to all experience. In exchange, we can know only appearances as they come through these frameworks, never the thing-in-itself beyond them. The Euclidean geometry he considered necessary was shaken by 19th-century non-Euclidean geometry.

• Immanuel Kant ↗
• Critique of Pure Reason ↗

Kant defined enlightenment as emergence from self-incurred immaturity: the courage to use one's own understanding without another's guidance.

Kant held that morality comes from duty, not consequences. Act only on principles you could will to be universal laws, and never treat a person merely as a means: the categorical imperative became the philosophical foundation of modern ideas of human dignity and human rights.

• Categorical imperative ↗

Bentham held that the right action is the one that produces the greatest happiness for the greatest number, and tried to apply a calculus of pleasure and pain to reforming laws and institutions. Judging morality by consequences, it is the opposite of Kant's deontology.

• Utilitarianism ↗

Mary Wollstonecraft argued that women seem inferior not by nature but because they are denied education, and that as rational beings equal to men they should be educated and enjoy rights.

Hegel saw reality as a process that unfolds itself, with Absolute Spirit as its subject. His dialectic, in which a position generates its opposite through internal contradiction and the two are reconciled at a higher level (Hegel himself almost never used "thesis–antithesis–synthesis"), and the master–slave dialectic, in which the laboring slave is the one who gains self-consciousness, are famous. Almost all later philosophy was built by carrying Hegel forward or reacting against him.

• Georg Wilhelm Friedrich Hegel ↗

Schopenhauer, who called Hegel a charlatan, held that Kant's thing-in-itself is in fact will, blind and endlessly striving. He taught a pessimism in which desire unfulfilled is pain and desire fulfilled is boredom, and sought salvation in art, asceticism and compassion. The first major Western philosopher deeply influenced by the Upanishads and Buddhism, he marks the first serious meeting of Eastern and Western philosophy.

Kierkegaard criticized Hegel's system for saying nothing about how a living individual should live. He emphasized not objective truth but subjective truth, the truth an individual holds with passion, and was the first to analyze anxiety philosophically, as the dizziness we feel before freedom.

• Søren Kierkegaard ↗

Marx and Engels turned Hegel's dialectic onto material production and economic relations and declared that what drives history is not spirit but class struggle. "Philosophers have only interpreted the world; the point is to change it." In Capital (1867) Marx analyzed the alienation workers suffer under capitalism and the system's contradictions. No philosophy did more to change the history of the 20th century.

• Karl Marx ↗
• The Communist Manifesto ↗

John Stuart Mill revised utilitarianism by arguing that pleasures differ in quality ("better to be a human being dissatisfied than a pig satisfied") and set out the harm principle: individual liberty cannot be restricted unless it harms others. He was also an early advocate of women's suffrage.

• On Liberty ↗

Peirce said the meaning of a concept lies in its practical consequences; William James said whether a belief is true is judged by how well it works in life; and Dewey extended the idea into theories of education and democracy.

Frege rebuilt logic from the ground up for the first time since Aristotle, laying the foundations of modern symbolic logic. His distinction between reference and sense, "the morning star" and "the evening star" refer to the same Venus but differ in meaning, became the starting point of the philosophy of language.

• Gottlob Frege ↗

Nietzsche diagnosed that, with modern science and the Enlightenment, Christian faith could no longer be the foundation of European culture, and that nihilism was coming as all the values built on it collapsed. He offered genealogy, which digs up the origins of morality; the will to power; the Übermensch, who creates values for himself; and eternal recurrence, the question of whether you could affirm this life if it repeated forever. After his death his sister distorted his work and the Nazis exploited it, though he himself despised antisemitism and German nationalism.

• Friedrich Nietzsche ↗
• God is dead ↗

Husserl founded phenomenology, which brackets our assumptions about the world and describes phenomena precisely as they appear to consciousness. Its key concept is intentionality: consciousness is always consciousness of something.

• Phenomenology (philosophy) ↗

Russell showed how the grammatical form of ordinary language hides its logical form, and from 1910, with Whitehead, tried in Principia Mathematica to derive all of mathematics from logic. He was jailed for his antiwar activism and won the Nobel Prize in Literature.

• Bertrand Russell ↗

Combining Zen Buddhism with Western philosophy, Nishida Kitarō built a philosophy of "pure experience" and "absolute nothingness" and founded the Kyoto School. It is regarded as the first systematic attempt by Eastern philosophy to express itself in the language of Western philosophy.

Saussure's posthumously published Course in General Linguistics saw language as a structure in which meaning arises from differences between signs, the starting point of structuralism. The same year Dewey published Democracy and Education, which emphasized learning through experience.

Wittgenstein saw language as a picture of the world, with meaningful sentences picturing facts. Ethics, God and the meaning of life then become what cannot be said. Believing he had solved all of philosophy's problems, he became a schoolteacher in a rural village.

• Ludwig Wittgenstein ↗
• Tractatus Logico-Philosophicus ↗

Heidegger said Western philosophy since Plato had dealt only with beings and forgotten the meaning of being itself. Humans are not subjects observing the world from outside but beings already thrown into the world and living in it (being-in-the-world), and only by facing their own death do they live authentically. His joining the Nazi Party in 1933 and serving as university rector still cast a heavy shadow over his philosophy.

• Martin Heidegger ↗
• Being and Time ↗

Carnap, Schlick and the Vienna Circle dismissed traditional metaphysics as meaningless with the verification principle: a meaningful sentence must be either logically true or verifiable by experience. Gödel attended their meetings too. But they ran into the problem that the verification principle itself cannot be verified.

• Logical positivism ↗

Popper said what separates science from non-science is not verifiability but falsifiability. No number of white swans proves "all swans are white," but a single black swan refutes it. It was one answer to Hume's problem of induction. Later, in The Open Society and Its Enemies, he criticized Plato, Hegel and Marx as roots of totalitarianism.

• Falsifiability ↗

Camus called the gap between humans who crave meaning and a silent world "the absurd," and found meaning in living like Sisyphus, endlessly rolling his boulder uphill, facing the absurd yet rebelling against it.

A knife's purpose is set before it is made, Sartre said, but a human being exists first and then makes what they will become. Since human nature is not fixed in advance, we are condemned to be free and bear full responsibility for our choices. He refused the Nobel Prize in Literature.

• Existentialism ↗

In exile, Adorno and Horkheimer of the Frankfurt School argued that Enlightenment reason had degenerated into instrumental reason that dominates nature and people, leading to barbarism such as Nazism.

Beauvoir analyzed how women had been defined in society as men's "Other." It is the starting point of modern feminist philosophy.

• The Second Sex ↗

Turing turned this question into a test: can a machine be indistinguishable from a person in conversation? Descartes's mind–body problem flared up anew in the computer age.

• Computing Machinery and Intelligence ↗

Quine attacked the very idea that sentences true by logic can be cleanly separated from sentences true by experience. Our beliefs face experience not one at a time but together, as a single web.

In this posthumous book, Wittgenstein criticized his own earlier philosophy. Language is used in countless activities, commands, jokes, prayers, greetings, and a word's meaning lies in its use within a language game. Many philosophical problems, he held, are confusions that arise when language leaves its everyday use.

• Philosophical Investigations ↗

Lévi-Strauss applied Saussure's linguistics to kinship systems and myths, exploring the structures that create meaning beneath individual consciousness.

Gadamer said understanding is a fusion of horizons, in which the interpreter's preconceptions and the horizon of the text meet in dialogue.

Kuhn argued that science does not progress by piling up knowledge step by step. Scientists solve problems within a shared framework, a paradigm, until unexplained anomalies accumulate and the paradigm itself is overthrown in a revolution. From geocentrism to heliocentrism, from phlogiston to Lavoisier, from Newton to Einstein: the book changed how the whole history of science is read.

• The Structure of Scientific Revolutions ↗

Watching the trial of an official responsible for carrying out the Holocaust, Hannah Arendt concluded that enormous evil came not from a monster but from an ordinary bureaucrat who followed orders without thinking. She also wrote The Origins of Totalitarianism.

• Eichmann in Jerusalem ↗

Derrida proposed deconstruction: binary oppositions that texts rely on, speech/writing, reason/emotion, hide a hierarchy that ranks one side above the other, and deconstruction reveals where that hierarchy undoes itself within the text.

Rawls argued that if we chose society's rules behind a veil of ignorance, not knowing whether we would be rich or poor or what talents we would have, we would choose principles that give the greatest benefit to the least advantaged. The book revived political philosophy, and in 1974 Nozick answered it with a libertarianism centered on individual property rights.

• A Theory of Justice ↗

Nagel argued that even if we knew everything physical about a bat's brain, we still could not know what it is like, subjectively, to be a bat.

In Discipline and Punish, Foucault carried on Nietzsche's genealogy, arguing that power works less by repressing from above than by watching and disciplining people in institutions such as schools, hospitals and prisons, producing "normal" subjects. The same year Peter Singer's Animal Liberation brought every being capable of suffering into ethics and opened the age of applied ethics.

• Michel Foucault ↗
• Animal Liberation (book) ↗

Searle argued that just as someone who knows no Chinese could manipulate symbols according to a rulebook and appear from outside to understand Chinese, a computer merely manipulates symbols and does not understand. It became the classic argument in the debate over whether AI truly understands.

• Chinese room ↗

Habermas, of the second generation of the Frankfurt School, argued that rather than abandoning reason, we should rebuild it as communicative rationality: people reaching agreement through rational discussion free of coercion.

Chalmers distinguished the "easy problems," explaining how the brain processes information, from the "hard problem": why that processing is accompanied by subjective experience at all. It sits at the center of today's debates about AI.

• Hard problem of consciousness ↗

Bostrom argued that if advanced civilizations run many simulations of their ancestors, it is likely that we are living in one. Descartes's demon returned in the language of computers.

• Simulation hypothesis ↗

Knobe, Nichols and others launched experimental philosophy, using surveys and experiments to test directly how much the intuitions philosophers take for granted vary across cultures and people.

Bostrom systematically examined the risks of artificial intelligence that surpasses humans and the problem of aligning its goals with human values. It helped make AI ethics and safety a major field of philosophy.

• Ethics of artificial intelligence ↗

With an engineer's claim that a conversational AI had become sentient and the rise of large language models, Turing's question, Searle's Chinese room and Chalmers's hard problem left the philosophy classroom and became questions for society as a whole. The mind–body problem Descartes left behind became the most practical of questions.

• Artificial consciousness ↗