A survey of the principal questions of philosophy across the world's major traditions, from the sixth century BCE to the present, with an assessment of which problems remain open and why.
This report surveys the history of philosophy in the inclusive sense: the recorded attempts, in every major civilization, to answer fundamental questions by argument rather than by appeal to authority alone. It proceeds chronologically from the earliest named thinkers to the present, and it closes with an extended assessment of the current state of the discipline -- which of its problems plausibly admit of solution, which are badly posed and require reformulation, and which concern the discipline's own methods.
For most of recorded history, the fundamental questions received answers that were transmitted rather than defended. The civilizations of Egypt, Mesopotamia, early China, and Vedic India possessed elaborate cosmologies, legal and moral codes, and substantial wisdom literatures: the Egyptian Instructions, the Babylonian dialogues on undeserved suffering, the early Upanishads. What these literatures generally lack is the practice that distinguishes philosophy from wisdom as such: the treatment of an answer as a claim to be defended against objections, such that the better argument, rather than the better pedigree, decides the matter.
That practice emerges, in several civilizations, within a remarkably narrow window.
Karl Jaspers coined the term "Axial Age" for the period in which Greece, India, China, Israel, and Persia each produced thinkers of the first rank, within a few centuries of one another and with little or no mutual contact. Whether this constitutes a single historical phenomenon or a coincidence magnified by hindsight remains disputed. What is not disputed is that the documentary record of systematic thought begins here.
Thales of Miletus, active around 585 BCE, held that everything is ultimately water. The interest of the claim lies not in its content, which is false, but in its form: it is a general thesis about the constitution of nature, offered without appeal to the gods and open to refutation. His successors developed the first sustained debates in metaphysics. Anaximander posited an indefinite first principle; Heraclitus made flux fundamental; Parmenides argued that change is impossible; Democritus resolved the world into atoms and void. Pythagoras contributed the conjecture that reality is at bottom mathematical -- a conjecture physics has never abandoned.
The later Upanishads advance a striking identity claim: the innermost self (atman) and the ground of all reality (brahman) are one. Around 500 BCE the Buddha argued for the contrary position -- that careful attention to experience discloses no persisting self at all, only a causally connected stream of psychological events, and that suffering arises from mistaking this stream for a substance. The subsequent Indian tradition developed the most technically demanding debate culture of the ancient world: Nyaya logicians formalized the theory of inference, while Buddhist and Hindu schools contested theories of perception, causation, and consciousness in continuous argument for over a thousand years.
Chinese philosophy took its founding problem from a political collapse, the disintegration of the Zhou order, and its question was accordingly practical: on what basis can a livable society be restored? Confucius answered in terms of cultivated character, ritual propriety, and the obligations of relationship. The Daoists, Laozi and Zhuangzi, located the disorder in striving itself and counseled alignment with the natural course of things. Mozi defended impartial concern for all persons -- a consequentialism anticipating Bentham by two millennia. The Legalists dismissed the appeal to virtue and argued for institutional design backed by incentive and punishment. These four positions -- character, spontaneity, impartial welfare, and institutional design -- continue to structure political philosophy's space of options.
The Hebrew prophets and Zoroaster contributed a conception rather than a method: history as a moral drama with a beginning, a contest between good and evil, and an end. In secularized form this narrative structure underwrites the later ideas of progress, revolution, and utopia. A great deal of Western thought, including much that regards itself as irreligious, runs on this inherited plot.
Socrates (470–399 BCE) wrote nothing, yet his method proved decisive for everything that followed: invite an interlocutor to define courage or justice, and then examine the definition until its inadequacy is plain. The method made rigorous self-examination the discipline's central activity. Athens condemned him to death for impiety and corruption of the young, and the trial fixed philosophy's enduring self-conception as an activity a city needs and resents in equal measure.
His student Plato constructed the first comprehensive philosophical system: the theory of Forms, on which the changing particulars of experience are imperfect instances of changeless intelligible patterns; the immortality of the soul; the ideally just city governed by philosophical knowledge; and, institutionally, the Academy. Whitehead's remark that the European tradition consists of footnotes to Plato overstates the case, but it identifies correctly where the agenda was set.
Plato's student Aristotle accomplished something of arguably greater consequence: the division of knowledge into disciplines. Logic, physics, biology, psychology, ethics, politics, rhetoric, and poetics were each given a domain, a method, and a body of results. His formal logic remained essentially without rival for over two thousand years. His ethics, which analyzes virtue as cultivated excellence and the human good as flourishing (eudaimonia), has returned to the center of the field within the last seventy years.
After Alexander, in a Greek world grown large and politically uncertain, philosophy turned to the therapeutic. The Hellenistic schools offered rival disciplines of tranquility. The Stoics taught the distinction between what is and is not within one's control; the Epicureans, the sufficiency of modest pleasures and the irrationality of the fear of death; the Skeptics, suspension of judgment as itself the path to peace. Stoicism became the dominant moral outlook of the Roman governing class, professed alike by the slave Epictetus and the emperor Marcus Aurelius; its recurrent modern revivals are the third or fourth in its history.
In India, the classical schools reached systematic form in the same centuries, and around 200 CE Nagarjuna produced one of the most radical arguments in the history of metaphysics: that nothing whatever possesses independent, intrinsic existence -- that all things are "empty" in the precise sense of being constituted entirely by their relations. Contemporary readers have noted, with due caution, the affinity between this doctrine and structuralist interpretations of modern physics.
For roughly a millennium, the central project of philosophy in three civilizations was the same: to reconcile an inherited Greek rationalism with a revealed religion, and to determine which of the two, at points of conflict, must yield.
Augustine (354–430) joined Platonism to Christianity and, in the course of doing so, made the inner life itself an object of philosophical analysis. The Confessions is the first sustained philosophical autobiography, and its treatments of time, memory, and the divided will remain part of the working literature. His admission concerning time -- that he knows what it is until asked to explain it -- is still a defensible summary of the state of the question.
The center of activity then passed to the Islamic world, which from roughly 800 to 1200 was the most sophisticated philosophical culture in existence. The Baghdad translation movement preserved and transmitted Aristotle. Al-Farabi systematized him. Avicenna (Ibn Sina) constructed an original metaphysics whose distinction between essence and existence shaped all subsequent medieval thought, and whose "floating man" argument -- that a person created in a sensory void would nonetheless be aware of himself -- anticipates the Cartesian cogito by six centuries. Al-Ghazali turned skeptical arguments against the philosophers' confidence in necessary causal connection, anticipating Hume; Averroes (Ibn Rushd) replied in defense of demonstrative reason, and his commentaries on Aristotle became the proximate cause of the philosophical revival in Latin Europe. Maimonides undertook the parallel reconciliation for Judaism.
Europe absorbed these results through the new universities of Bologna, Paris, and Oxford, which made philosophy for the first time a professional discipline with curricula and examinations. Aquinas (1225–1274) produced the great synthesis of the age, an integration of Aristotle with Christian doctrine spanning God, nature, law, and ethics that remains the official framework of Catholic thought. The late Scholastics then loosened the structure from within: Duns Scotus and William of Ockham -- of the razor -- argued that only particulars exist and that the divine will cannot be constrained by human reason, positions which had the unintended effect of separating natural inquiry from theology.
The synthesis was not a Western monopoly. In India, Adi Shankara (c. 800) carried Upanishadic non-dualism to its systematic completion. In China, Zhu Xi (1130–1200) constructed Neo-Confucianism, a metaphysics of pattern (li) and vital force (qi) supporting Confucian ethics, which became the examination curriculum of the imperial bureaucracy for seven centuries. No philosopher in history has exercised comparable institutional authority.
Renaissance humanism recovered the full ancient corpus. Machiavelli refounded political theory on the observation of how power is in fact acquired and held, rather than on how it ought to be; Montaigne invented the essay and with it a new philosophical persona, the skeptic examining himself without the protection of a system.
The decisive event, however, came from outside philosophy. Copernicus, Galileo, Kepler, and finally Newton demonstrated that celestial and terrestrial motion obey the same mathematical laws. This destroyed the Aristotelian world-picture on which all three scholastic civilizations had built, and it reoriented philosophy's agenda from the question of what exists to the question of how knowledge is possible at all. Epistemology held the center of the discipline for the next three hundred years.
Descartes (1596–1650) gave the reorientation its canonical form: doubt everything that can be doubted, and determine what survives. What survives is the thinker's certainty of his own existence -- and with it the modern conception of mind as an inner realm known immediately, set over against an external world known only by inference. His division of reality into thinking substance and extended substance created the mind-body problem in the form it still takes. Spinoza answered that there is exactly one substance, God or Nature, the two names denoting the same thing -- a doctrine for which his community expelled him. Leibniz answered with an infinity of mind-like simple substances, while independently inventing the calculus.
The empiricists argued the contrary program: that all knowledge derives from experience. Locke analyzed the mind as initially unfurnished and, in political philosophy, government as a revocable trust for the protection of natural rights; the American founding documents are in large part applied Locke. Hume then pursued empiricist principles to their unwelcome conclusions: that we never observe causal connection, only constant conjunction; that inductive inference from past to future admits of no non-circular justification; and that the self, sought in experience, resolves into a bundle of perceptions -- a conclusion the Buddhist tradition had reached by a different route two millennia earlier. Hume's problems have not been solved; they have been managed. Modern statistics and machine learning are, in effect, sustained negotiations with them.
Kant (1724–1804), roused by Hume from what he called his dogmatic slumber, proposed the most consequential single hypothesis in modern philosophy: that the mind does not passively receive the world but actively structures it. Space, time, and causality, on this view, are not features of things as they are in themselves but forms the understanding imposes on experience; we can have necessary knowledge of the world as experienced precisely because we contribute its structure. His ethics was of comparable influence: morality as rational self-legislation, whose supreme principle commands acting only on maxims one could will as universal law and treating persons always as ends, never merely as means. The contemporary language of human rights is substantially Kantian in its architecture.
The nineteenth century developed in several directions at once, most of them departures from Kant.
Hegel historicized everything: reality as a rational process unfolding through contradiction and resolution, with freedom as its direction. Marx retained the historical engine and replaced its fuel -- the driver of history is not the development of ideas but the organization of material production and the struggle between classes -- and declared that the point of philosophy is not to interpret the world but to change it. Whatever one's verdict on the doctrine, roughly a third of humanity spent the twentieth century under states claiming its authority; no philosophy has been subjected to a larger experiment.
Bentham and Mill developed utilitarianism -- the thesis that right action maximizes aggregate happiness -- into the working logic of legislation, economics, and public administration. Mill's On Liberty, with its principle that the only legitimate ground for coercion is the prevention of harm to others, remains the standard framework for debates about free expression.
Kierkegaard and Nietzsche, from opposed premises, attacked the ambition of system itself. For Kierkegaard, the truth that matters is subjective -- lived, chosen, incapable of capture in a system. Nietzsche's announcement that God is dead was a diagnosis, not a boast: European civilization, he argued, no longer believes its own foundations, and the question is whether it can create values to replace those it inherited or will subside into nihilism. As prophecy concerning the twentieth century, this has worn well.
Darwin, though no philosopher, may have altered philosophy more than any philosopher of the century: design without a designer, mind as an evolved organ, humanity continuous with the animals. Every branch of the discipline is still assimilating the result.
In the United States, Peirce, James, and Dewey founded pragmatism, the one philosophical tradition of American origin: the meaning of a conception lies in its practical consequences, and truth is what inquiry, pursued indefinitely, would converge upon. Long dismissed as insufficiently rigorous, pragmatism has quietly reentered the field's mainstream.
Around 1900, Western philosophy divided into two traditions that conducted largely separate conversations for most of the century.
Frege reconstructed logic on new foundations -- the first fundamental advance since Aristotle -- and argued that the analysis of thought must proceed through the analysis of language. Russell and Moore converted this into a method: resolve philosophical problems into precise components and examine the logical form of the sentences in which they are stated. Wittgenstein holds the unusual distinction of having produced two opposed philosophies of the first importance: the early doctrine that language pictures the world and that what cannot be so pictured cannot be said; and the later doctrine that meaning is use, that language comprises a plurality of social practices, and that many philosophical problems are grammatical confusions to be dissolved rather than solved. The logical positivists of Vienna attempted to eliminate metaphysics and normative ethics as strictly meaningless, on the ground that only verifiable statements have cognitive content; the program collapsed when it became clear that the verification principle fails its own test. Quine then argued that no principled line separates philosophy from empirical science, and Kripke, in the 1970s, restored metaphysics to respectability within the analytic idiom. That idiom -- clarity, explicit argument, tractable subproblems -- now governs most English-language academic philosophy.
Husserl founded phenomenology as the disciplined description of conscious experience prior to theory. Heidegger redirected it toward the question of Being and an analysis of human existence as thrown, temporal, and constituted by its relation to death -- work of enormous influence, permanently compromised by its author's Nazism. Sartre, Beauvoir, and Camus gave existentialism its public form: existence precedes essence, the human being is what it makes of itself, and anguish is the price of that freedom. Beauvoir's The Second Sex, with its thesis that one is not born but becomes a woman, effectively founded modern feminist philosophy. The Frankfurt School -- Adorno, Horkheimer, later Habermas -- asked how the Enlightenment could have issued in Auschwitz, and built critical theory as the answer. Structuralism and post-structuralism, above all Foucault on the entanglement of power and knowledge and Derrida on the instability of meaning, subsequently transformed the humanities at large, supplying the vocabulary of discourse and social construction that now pervades public argument.
Philosophy of science conducted its own central drama. Popper proposed falsifiability as the criterion demarcating science from non-science; Kuhn argued from the historical record that science advances not by smooth accumulation but through paradigm shifts -- a term whose subsequent career in ordinary usage he came to regret. In political philosophy, Rawls ended decades of quietism in 1971 with a single construction: principles of justice are those that would be chosen behind a veil of ignorance, in ignorance of one's own position in society. Nozick replied within three years on behalf of libertarian entitlement, and the resulting opposition -- fairness against liberty, redistribution against holdings justly acquired -- remains the deep structure of most Western political debate. Applied ethics expanded rapidly in the same period, in medicine, in the treatment of animals following Singer, in business and the environment, returning philosophers to hospitals and legislatures for the first time in centuries.
Philosophy today is larger, more professionalized, more empirically engaged, and more global than at any previous point in its history -- and, at the same time, less certain of its own methods. Six developments characterize the period.
David Chalmers's 1995 formulation of the hard problem -- why is information processing accompanied by subjective experience at all? -- reorganized the philosophy of mind. Neuroscience continues to map correlations between neural states and experiences, but the explanatory gap has not narrowed: no account yet explains why a given pattern of neural activity should constitute, rather than merely accompany, the taste of coffee. The positions now seriously defended range from orthodox physicalism through illusionism, on which consciousness is not what it introspectively seems, to panpsychism, on which experience is a fundamental feature of matter -- a view that has moved, within two decades, from the margins to the refereed journals. A prominent adversarial collaboration in 2023 tested two leading neuroscientific theories of consciousness against each other; the fair summary of the result is that both were damaged and neither confirmed.
The most consequential development of the current decade is that questions philosophy incubated for centuries -- What is understanding? In virtue of what do words mean anything? What confers moral status? Can "good" be specified precisely enough to be implemented? -- have become engineering requirements. The alignment problem, that of ensuring that powerful optimizing systems reliably pursue what their designers actually value, is recognizably the is-ought gap and the central problems of meta-ethics restated as specifications. Large language models have unsettled the older landmarks: Searle's Chinese Room and the Turing test both read differently in the presence of systems that produce fluent philosophical prose while the question of whether anything is understood remains open. The moral status of artificial systems, until recently a topic for fiction, now has a small but serious research literature.
Experimental philosophy subjects the discipline's traditional evidence -- intuitions about cases -- to empirical study, and finds that such intuitions vary with culture, framing, and order of presentation, with uncomfortable implications for the authority of the armchair. Formal epistemology imports probability theory; philosophy of physics engages the interpretation of quantum mechanics, where the dispute among many-worlds, collapse, and hidden-variable theories remains genuinely unresolved after a century; moral psychology reads the neuroimaging literature. The boundary between philosophy and science, once policed with confidence, is now an open frontier in both directions.
The discipline has begun to treat Indian, Chinese, Islamic, Africana, Latin American, and Indigenous philosophy as philosophy, rather than consigning them to religious studies. The motive is partly justice and partly self-interest: these traditions contain sophisticated, independently developed positions on precisely the problems -- the self, consciousness, the metaphysics of relations, the ethics of role and relationship -- on which the Western literature is most visibly stalled. Comparative work that would have been professionally hazardous in 1980 is now published in the leading journals.
The Rawlsian framework presupposed reasonably stable liberal democracies deliberating in good faith. Polarization, populism, and algorithmically mediated speech have undermined the presupposition, and the most vital current work has migrated to social epistemology: the analysis of echo chambers and epistemic bubbles, of testimonial injustice -- Miranda Fricker's term for the wrong of being disbelieved on account of who one is -- and of what truth-conducive public discourse requires when the information environment is curated by optimization. The twentieth century's problem was propaganda from above; the present century's is epistemic degradation from everywhere at once.
Nietzsche's forecast has come due. Institutional religion has receded across the developed world more rapidly than anything has replaced it, and the question of meaning -- as distinct from happiness -- has returned from its exile in the self-help literature to serious philosophical work on secular meaning, on the revival of Stoic practice, and on what some now call the meaning crisis. The scale of public appetite for philosophical material, from trade books to lecture audiences, indicates that demand for the discipline's oldest product remains strong; what changed was the channel of distribution.
The question of what philosophy must do to advance admits of a useful three-fold division. Some problems plausibly have answers not yet found, and require solution. Some are badly posed, and progress consists in reformulating them. And some concern not the problems but the discipline's own machinery, and require repair. I take these in turn, ordered roughly by what depends on each.
Consciousness. The hard problem is the discipline's summit, and its practical stakes have risen sharply: absent a theory of what generates experience, we cannot determine whether an artificial system, a brain organoid, or a cephalopod feels anything -- and we are building and using all three. This may be the first period in which a theory of consciousness is a practical necessity rather than a speculative luxury. The plausible routes forward are adversarial collaboration among neuroscientific theories, which has begun; a more rigorous bridge between first-person phenomenological description and third-person science; or the sober conclusion that the question itself requires reformulation, as the illusionists maintain.
The specification of value. The alignment problem has forced meta-ethics to deliver or admit that it cannot. If consequential decisions are to be delegated to optimizing systems, "good" must be specified precisely -- and every precise specification so far proposed, whether the satisfaction of preferences, conformity to rules, or the imitation of human judgment, fails in known ways under optimization pressure. Two adjacent problems remain equally open. The first is aggregation: how the large loss of one person weighs against the small gains of many. Every formal answer, utilitarian summation included, generates monstrous results at the limits, of which Parfit's repugnant conclusion is the best known. The second is moral uncertainty: how one ought to act when uncertain which moral theory is true -- a question scarcely formulated twenty-five years ago that now sustains a serious literature. These problems have the shape of solvable ones: they are formal, constrained, and equipped with clear criteria of failure.
Induction and scientific realism. Hume's problem was never solved; it was engineered around. Machine learning has renewed it in contemporary dress: distribution shift, generalization beyond the training data, and the conditions under which a model's predictive success warrants belief in its picture of the world are the problem of induction and the realism debate conducted on new hardware. Philosophy of science and learning theory are visibly converging here, and genuine progress -- formal results specifying when generalization is justified -- appears possible.
The interpretation of quantum mechanics. A century old, still open, and not a merely verbal dispute: the many-worlds, collapse, and hidden-variable interpretations describe different realities and may yet differ empirically. However the question resolves, the metaphysics of the textbooks will require rewriting.
Free will. The majority position among professionals, at roughly six in ten, is compatibilism: the freedom worth wanting -- action from one's own reasons, responsive to evidence, free of coercion -- is compatible with determinism, and the libertarian alternative, on which one could have done otherwise in an identical universe, was never coherent. The needed work is downstream of the analysis. Our institutions of blame, punishment, and desert still presuppose the folk conception, and the reconstruction of responsibility practices -- above all in criminal justice -- to fit what is actually defensible is among philosophy's largest undischarged obligations.
Personal identity. The question whether a person at one time is the same person as a person at another was a seminar exercise so long as the cases were imaginary. The cases are no longer imaginary: radical life extension, brain-machine interfaces, digital reconstructions trained on a person's records, personality change under dementia and deep-brain stimulation. Parfit argued in 1984 that identity is not what matters; psychological continuity matters, and it admits of degrees. The required reformulation is to abandon the binary question and rebuild the legal and ethical concepts that presuppose it -- consent, contract, punishment, survival -- on gradational foundations. Very little of that reconstruction has been attempted.
The self. Buddhist analysis, Hume, and contemporary cognitive science converge on the conclusion that the unified persisting self is a construction. Western ethics, law, and economics treat the construction as load-bearing. Reconciling the two -- preserving agency and responsibility while discarding the substantialist picture -- is a genuine research program spanning traditions, and one of the places where the opening of the canon pays immediate dividends.
Meaning. The question of life's meaning requires its own reformulation, from the cosmic to the constructive: granted that no purpose is built in, what distinguishes meaningful lives from merely pleasant ones, and can a secular culture transmit whatever the answer is at scale, as the traditions once did? The problem is half philosophy and half institutional design, and the evidence of demand reviewed above suggests it is not going away.
The problem of intuitions. Philosophy's principal evidence consists of considered judgments about cases. Experimental philosophy has shown these judgments to vary with culture, wording, and order of presentation. The alternatives are unattractive in different degrees: defend the method rigorously, specifying whose intuitions carry weight and why; supplement it systematically with formal and empirical methods; or concede that substantial parts of the literature rest on sand. This is the discipline's replication crisis, proceeding in slow motion.
The problem of disagreement. Chart 04 states the difficulty plainly: able people, trained alike and reading the same evidence, divide evenly on central questions for centuries. The epistemology of peer disagreement implies that this should reduce everyone's confidence; the field mostly proceeds as though it did not. Metaphilosophy -- the study of what philosophical progress is and what settling a question would even consist in -- has become an active area precisely because the difficulty became impossible to ignore. One serious view holds that philosophy's characteristic product is not consensus but the disciplined mapping of option-spaces and the sharpening of questions: the discipline functions as the research laboratory from which the sciences successively spin off -- physics, psychology, linguistics, economics, and computer science each began as philosophy -- while retaining the questions that resist spin-off. On that view the enterprise is in reasonable health, though its progress is systematically invisible to those who measure progress by consensus.
The problem of integration. Analytic and continental methods, and now several world traditions, still proceed largely in parallel. The problems just enumerated -- the self, consciousness, meaning -- lie exactly at their intersection. The infrastructure of genuine synthesis, scholars trained in more than one tradition and journals prepared to referee such work, is only now being built.
Collective epistemology. The classical theory of knowledge was constructed for a single inquirer forming beliefs. Our actual epistemic condition is networked: nearly everything anyone believes rests on testimony filtered through institutions and, increasingly, through optimizing systems. A rigorous account of when a collective -- a science, a platform, a polity -- is truth-conducive, and of how such collectives may be designed, is arguably the most practically urgent open problem in the discipline. It is also young enough to move quickly.
Forecasting intellectual history is a reliable method of embarrassing oneself before posterity; what follows are extrapolations of visible trends, not predictions.
The philosophy of mind and the study of artificial intelligence will merge. Within a generation it will seem strange that the nature of understanding was studied in one building and systems that arguably possess or lack it were built in another. The likely consolidation resembles that by which natural philosophy became physics. The question of moral status -- of artificial systems, organoids, and animals -- will in all probability be the defining applied-ethics dispute of the period, occupying the position that the boundaries of moral concern have occupied in every previous century.
Ethics will become quantitative without becoming utilitarian. Moral uncertainty, aggregation, risk, and long-run effects are receiving formal treatments that do not presuppose the summation of utility. A workable decision theory for action under moral uncertainty would be the most significant practical result in ethics in a century, and its components are visibly under construction.
The global synthesis will actually occur. The likeliest source of fundamentally new ideas is not an individual of genius but the collision of traditions that developed in isolation for two millennia and are now, for the first time, fully in contact with one another and with cognitive science. The self and consciousness are where that collision is presently hottest.
Social epistemology will become a design discipline. Truth-conducive institutions -- adversarial collaboration, prediction markets, the epistemic architecture of platforms and of AI-mediated information -- are moving from analysis to construction. The next figure of Rawls's stature may be whoever produces the definitive account of a healthy collective epistemic system; every democracy currently requires one, and none possesses one.
The perennial core will remain perennial. Every era has believed itself on the point of completing philosophy -- the positivists allowed the task a decade -- and every era has instead added a wing to the building. The safest claim in this report is that in 2126 the questions of what exists, what can be known, and how one ought to live will still be under dispute, and not necessarily only among humans. The questions persist not because our knowledge is defective but because they are constitutive of the kind of being that asks them.
Chart 01 is a qualitative reconstruction: theme shares were estimated from the standard historical record -- which figures and schools dominated each period, and what they worked on -- normalized to 100 percent per period, with the Western, Indian, Chinese, and Islamic traditions weighted together. It should be read as an argument in graphical form rather than a measurement. Chart 02 follows conventional periodizations; the peak bands are judgment calls, and reasonable historians would shade them differently. Chart 03 synthesizes the relative volume of current journal output and PhilPapers category activity, and should be treated as indicating orders of magnitude. Chart 04 reports approximate figures from the 2020 PhilPapers Survey (Bourget and Chalmers), the largest survey of professional philosophers yet conducted; exact percentages vary with the treatment of "lean toward" responses. Dates for ancient figures are approximate throughout; scholarly ranges exist for nearly every date before 1000 CE.