In December 1784 the Berlin journal Berlinische Monatsschrift published a short essay that would become the most quoted definition of an entire century: “Answering the Question: What Is Enlightenment?” (Beantwortung der Frage: Was ist Aufklärung?) by Immanuel Kant. The question had been raised in the journal itself by Johann Friedrich Zöllner, a clergyman and Prussian official, who had remarked in a footnote in December 1783 that no one had yet answered satisfactorily what “Aufklärung” is, a word then in wide circulation without a precise definition. That the age of the Enlightenment had to ask itself publicly what it was says a good deal about the movement. From the start it was a reflection on itself, on the limits and rights of reason, and on who may exercise them.

This article presents the Enlightenment as a set of diverse intellectual projects, not always coherent with one another, that developed in Europe and the Americas during the eighteenth century. It begins with Kant’s definition, surveys the leading French, English, Scottish, and German authors, examines the internal tensions (with Rousseau as the best-known critic from within), and closes with the major later objections, from the so-called Counter-Enlightenment to the Dialectic of Enlightenment, and with the debate over legacy.

One Movement, Many Names

The variety of words already signals the variety of the phenomenon: les Lumières in French, the Enlightenment in English, Aufklärung in German, Illuminismo in Italian, la Ilustración in Spanish. All rely on the metaphor of light, set against the darkness attributed to superstition, unexamined tradition, and imposed authority.

Chronological boundaries are conventions. The high point is usually placed between the end of the seventeenth century (the “crisis of the European conscience,” in the historian Paul Hazard’s phrase) and the French Revolution, but the markers vary by author. Historians also disagree about whether one may speak of a single Enlightenment. Peter Gay, in The Enlightenment: An Interpretation (1966–1969), argued for a basic unity, a family of thinkers who shared the idea of submitting everything to critical examination, while others, such as Jonathan Israel, distinguished a “radical” Enlightenment of Spinozist lineage from a “moderate” one. Readers should keep in mind that “the Enlightenment” is partly a category constructed retrospectively.

Philosophically, several recurrent traits can be identified, with the caveat that none is shared by every author of the period:

  • Confidence in reason as the instance for examining beliefs, institutions, and customs, tied to the scientific revolution of the seventeenth century (Newton, Galileo) and to the methods of Francis Bacon and Descartes;
  • The primacy of experience and empirical method, especially in the tradition of Locke and Hume (see the glossary entry on empiricism), alongside the persistence of the rationalism of Leibniz and Wolff in Germany;
  • Criticism of traditional religious and political authority, in widely varying degrees: from deism and toleration to the open atheism of some materialists;
  • Interest in human nature and society as objects of study, with the first sketches of the social sciences;
  • The idea of progress in knowledge and, for many, in morals and institutions;
  • Cosmopolitanism and the language of rights, which would feed the declarations of 1776 and 1789.

Kant: Leaving Immaturity

The 1784 essay opens with a sentence that became emblematic. Enlightenment, Kant writes, is the human being’s emergence from his self-incurred immaturity (selbstverschuldete Unmündigkeit). Immaturity is the inability to use one’s own understanding without the guidance of another. It is “self-incurred” when its cause lies not in a lack of understanding but in a lack of resolution and courage to use it without direction from someone else. Hence the motto Kant proposes: Sapere aude! “Have the courage to use your own understanding!”

The Latin phrase comes from Horace’s Epistles (I, 2, 40); Kant restates it in German and turns it into the banner of the whole age. Two points in the text deserve particular attention.

First, the diagnosis of laziness and cowardice. Kant observes that it is convenient to be a minor: if I have a book that thinks for me, a pastor who has a conscience for me, a physician who decides my diet, I need not exert myself. The guardians, for their part, see to it that the great majority regards the step to maturity as dangerous. Enlightenment is therefore both an intellectual program and a problem of character and social conditions.

Second, the distinction between the public and the private use of reason. Kant calls public the use one makes of reason “as a scholar before the reading public,” and private the use one makes of it in a civil post or office (an officer, a tax collector, a clergyman in the pulpit). The public use must be free; the private use may be restricted. The officer must obey an order, yet may, as a scholar, publicly criticize the military service. Kant attributes to Frederick II of Prussia a maxim to this effect: argue as much as you like and about whatever you like, but obey. The formulation has been read in opposite ways, as a prudent defense of gradual reform or as an excessive concession to enlightened despotism, and the debate among commentators continues.

Kant does not claim to live in an enlightened age. In his assessment he lived in an age of enlightenment, a process under way and unfinished. The nuance is decisive: Enlightenment is a task, not an achieved state.

The essay should be read alongside the critical philosophy. In the Critique of Pure Reason (1781), Kant makes reason itself the tribunal that examines its own claims and fixes its limits. His ethics of autonomy carries the motif into the practical domain: the free will is the one that gives itself the law, in contrast to the heteronomy of obedience to an external authority (see also Kant: Ethics, Categorical Imperative, Duty, and Autonomy and the entry on autonomy). The profile of Kant presents his work as a whole.

One fact is often recalled: Kant was not the first to answer Zöllner’s question. Moses Mendelssohn had published in the same journal, a few months earlier, a text titled “On the Question: What Does It Mean to Enlighten?” According to Kant’s own note at the end of the essay, he had not yet read Mendelssohn’s text when he wrote his own. The two answers, gathered in collections such as the one edited by James Schmidt (What Is Enlightenment?, 1996), show how contested the concept was even among friends.

France: Toleration, Laws, Encyclopedia

Voltaire and the Cause of Toleration

François-Marie Arouet, known as Voltaire (1694–1778), is the most recognizable face of the French Enlightenment, less for systematic originality than for his gifts as popularizer and polemicist. After exile in England he published the Philosophical Letters (Lettres philosophiques, 1734), praising English religious toleration, Locke’s empiricism, Newtonian physics, and English institutions, in implicit contrast to France. In Candide, or Optimism (1759) he satirized the thesis that “all is for the best,” which he ascribed (questionably) to Leibniz; for Leibniz’s actual doctrine see the article on the Monadology and theodicy.

The Treatise on Tolerance (Traité sur la tolérance, 1763) grew out of the Calas affair. Jean Calas, a Protestant merchant of Toulouse, was executed in 1762 on the charge of having killed his son to prevent his conversion to Catholicism. Voltaire took part in the campaign to rehabilitate the condemned man, which succeeded in 1765. The treatise combines the legal argument of the case with a general defense of toleration and a critique of fanaticism. Voltaire’s position must be read in context: his toleration is that of a deist who fought the power of the Church, and his thought has limits and contradictions that later scholarship discusses, including with regard to Jews and non-European peoples.

Montesquieu: Politics as a Science of Laws

Charles-Louis de Secondat, Baron de Montesquieu (1689–1755), mocked French customs in the Persian Letters (1721) and in 1748 published The Spirit of the Laws (De l’esprit des lois), a work that seeks to understand the variety of laws and governments in relation to climate, geography, religion, customs, and each people’s “general spirit.” He distinguishes three forms of government, republic, monarchy, and despotism, each with its own “principle” (virtue, honor, fear). In Book XI, analyzing the constitution of England, he formulates the separation of powers (legislative, executive, judicial) as a condition of political liberty: to prevent the abuse of power, power must check power. The influence of this idea on modern constitutions, beginning with the American one, is widely acknowledged, while historians debate how faithful Montesquieu’s account of the English regime was.

Diderot, d’Alembert, and the Encyclopédie

The most characteristic collective achievement of the age was the Encyclopédie, ou Dictionnaire raisonné des sciences, des arts et des métiers, edited by Denis Diderot (1713–1784) and Jean le Rond d’Alembert (1717–1783). Published between 1751 and 1772, it comprised seventeen volumes of text and eleven of plates (the text volumes were completed in 1765 and the plates in 1772), to which later supplements and indexes were added. D’Alembert wrote the celebrated Preliminary Discourse (1751), which sets out a genealogy of human knowledge, Baconian and Lockean in inspiration, and the spirit of the enterprise; he left the editorship in 1758 after the controversy over his article “Geneva.” Diderot remained as editor and wrote a great many entries.

The Encyclopédie gathered hundreds of contributors, gave the “mechanical arts” a dignity equal to letters and sciences, and faced censorship and suspensions throughout its publication. Its philosophical significance lies in treating knowledge as a collective, open undertaking, organized alphabetically and by cross-references, rather than as a closed system resting on authority. Not all contributors shared the same convictions: the enterprise housed deists, skeptics, and, in Diderot and others, materialist leanings.

Rousseau: The Internal Critic

Jean-Jacques Rousseau (1712–1778) contributed to the Encyclopédie (chiefly articles on music and the entry “Political Economy”) but became the principal critic of Enlightenment optimism from within, and eventually broke with Diderot and Voltaire. In the Discourse on the Sciences and Arts (1750) he argued that the progress of the sciences and arts did not correspond to moral progress; in the Discourse on the Origin and Foundations of Inequality among Men (1755) he traced a conjectural history of inequality and the corruption of social life. In The Social Contract and Emile (both 1762) he proposed, on one side, a theory of popular sovereignty and the general will and, on the other, a pedagogy of natural formation and conscience.

It is debatable whether Rousseau should simply be classified as “against” the Enlightenment. His critique of civilization shares with the movement the critical examination of institutions, the appeal to liberty and equality, and the refusal to ground legitimacy on tradition alone. His importance for Kant was explicit: Kant himself acknowledged that reading Rousseau taught him to respect the ordinary human being. On political theory see the article The Social Contract: Hobbes, Locke, Rousseau, and on pedagogy Philosophy of Education.

Hume and the Scottish Enlightenment

In Scotland the Enlightenment had its own character: less anti-religious and more oriented toward the “science of man” and the history of civil society. David Hume (1711–1776), author of the Treatise of Human Nature (1739–1740) and the Enquiry concerning Human Understanding (1748), applied the experimental method to philosophy, analyzed causation and induction, and subjected religion and miracles to skeptical scrutiny (see Hume: Empiricism, Causation, Induction, and the Is–Ought Problem). Kant said in the Prolegomena (1783) that Hume’s warning had awakened him from his “dogmatic slumber.”

Around Hume grew a remarkable generation: Francis Hutcheson, who formulated an ethics of the moral sense; Adam Smith, author of the Theory of Moral Sentiments (1759) and The Wealth of Nations (1776); Adam Ferguson, with his Essay on the History of Civil Society (1767); and Thomas Reid, critic of Hume and founder of the philosophy of common sense. These authors developed an inquiry into the genesis of institutions, commerce, and customs that anticipates sociology and political economy.

The German Aufklärung

In Germany the Enlightenment unfolded across a mosaic of principalities, often under the patronage of reforming sovereigns (“enlightened despotism”), and had a strong religious and pedagogical component. The rationalist heritage of Leibniz and Christian Wolff supplied the vocabulary, and public discussion took place in periodicals such as the Berlinische Monatsschrift.

Gotthold Ephraim Lessing (1729–1781) is the central literary figure. In Nathan the Wise (Nathan der Weise, 1779) he defended toleration among Judaism, Christianity, and Islam through the famous parable of the three rings; in The Education of the Human Race (Die Erziehung des Menschengeschlechts, 1780) he interpreted the history of religions as a gradual pedagogy of humanity. Moses Mendelssohn (1729–1786), Lessing’s friend and an inspiring figure of the Haskalah (the Jewish Enlightenment), defended in Jerusalem (1783) the separation of the powers of state and religion and freedom of conscience, without renouncing his Jewish faith.

Kant, as seen, is the critical culmination of this tradition. At the same time, his transcendental philosophy fixes limits to theoretical reason that challenge the dogmatic optimism of part of the century’s rationalism: pure reason, when it speculates beyond possible experience, falls into antinomies.

Condorcet and the Idea of Progress

The Marquis de Condorcet (1743–1794), mathematician, philosopher, and politician, wrote while in hiding during the Terror, having been proscribed, the Sketch for a Historical Picture of the Progress of the Human Mind (Esquisse d’un tableau historique des progrès de l’esprit humain), published posthumously in 1795. The book divides human history into ten epochs, the last devoted to the future, and maintains the indefinite perfectibility of the human mind: the progress of the sciences, the spread of education, the reduction of inequalities between nations and between individuals. Condorcet died in prison in 1794.

The Sketch is usually read as the fullest expression of the Enlightenment philosophy of history. Its optimism was taken up, differently, by Auguste Comte, who saw in Condorcet a precursor of the law of three stages (see the article on positivism). For the broader debate see Philosophy of History: Meaning and Progress. One caveat: the idea of progress was not unanimous even within the century. Rousseau, as seen, questioned it, and Kant regarded it as a regulative postulate of practical reason rather than an empirical law.

The Critics: From the Counter-Enlightenment to the Dialectic of Enlightenment

Hamann and Herder

Objections arose within German culture already in the eighteenth century. Johann Georg Hamann (1730–1788), the “Magus of the North,” opposed to abstract reason the primacy of faith, language, and concrete experience; in 1784 he wrote a critique of Kant, the Metacritique on the Purism of Reason, which was published only posthumously. Johann Gottfried Herder (1744–1803), a student of Kant and later his critic, published in 1774 Another Philosophy of History for the Education of Humanity, which rejects the idea of a single scale of progress by which all cultures would be measured, and holds that each age and each people has its own center of gravity and intrinsic worth. Herder’s emphasis on language, cultural diversity, and historical belonging is often cited as one of the sources of historicism and Romanticism.

The Counter-Enlightenment Thesis (Berlin)

The historian of ideas Isaiah Berlin (1909–1997) popularized the expression “Counter-Enlightenment” in his essay of that name, published in 1973 in the Dictionary of the History of Ideas and later collected in Against the Current. In it Berlin describes a current of thinkers, notably Vico, Hamann, and Herder, along with Joseph de Maistre, who opposed the rationalism, universalism, and empiricism attributed to the Enlightenment. In other writings (above all The Roots of Romanticism), Berlin ascribes to the rationalist tradition that culminates in the Enlightenment three assumptions: that all genuine questions have a true answer, that these answers are knowable, and that they are compatible with one another. Herder’s and the Romantics’ critique of the idea of a single solution fed the value pluralism Berlin would defend in his own philosophy.

The category is contested. Recent scholars object that it concentrates too much on Germany and that the Enlightenment was more plural and less “naively rationalist” than the caricature implicit in the thesis; some reject the term itself. In any case it is a historiographical instrument, not a school.

Burke and the Conservative Critique

After 1789 the French Revolution became the terrain of dispute. Edmund Burke (1729–1797), in the Reflections on the Revolution in France (1790), criticized the pretension to rebuild society from abstract principles of reason and universal rights, defending the value of tradition, of prejudices accumulated through experience, and of gradual reform. One should not oversimplify: Burke was not an enemy of the Enlightenment in general, and he sympathized with the cause of the American colonists; his critique is directed at a certain political rationalism. For their part, defenders of the Revolution such as Thomas Paine replied in defense of natural rights.

Horkheimer and Adorno: The Dialectic of Enlightenment

In the twentieth century the most influential critique came from Max Horkheimer and Theodor Adorno, exiled from Nazi Germany, in Dialectic of Enlightenment (Dialektik der Aufklärung). The book circulated in 1944 in a mimeographed edition under the title Philosophische Fragmente and was published in 1947 by Querido in Amsterdam. The central thesis is that Enlightenment, understood broadly as the advance of thought that seeks to free human beings from fear and install them as masters, reverts to myth: in seeking to dominate nature through a reason that reduces everything to calculation and control, it becomes instrumental reason, and the domination of external nature turns into the domination of human beings over themselves and over others. The authors seek the marks of this dialectic in episodes of the Odyssey and in authors such as Kant and Sade, and apply the idea to the analysis of the “culture industry.”

The work, written under the impact of Nazism and Fascism, is not a simple repudiation of the Enlightenment: the authors state that freedom in society is inseparable from enlightened thought, and that the goal is an enlightenment that reflects on itself. This reading is discussed in detail in the article on the Frankfurt School. Jürgen Habermas, heir of Critical Theory, revisited the debate in The Philosophical Discourse of Modernity (1985) and in his 1980 lecture “Modernity: An Unfinished Project,” arguing that the Enlightenment project should be continued and corrected rather than abandoned, relying on a communicative rationality broader than the instrumental. Michel Foucault, in “What Is Enlightenment?” (1984), reinterpreted Kant’s text as the expression of a critical “attitude” of modernity rather than a doctrine.

Other Objections

Further criticisms are of more recent origin and are debated in the literature: that the universality proclaimed by the Enlightenment coexisted, in many of its authors, with racial theories, with the justification or toleration of slavery and colonialism, and with the exclusion of women from full citizenship. Thinkers such as Hume and Kant, for example, wrote passages on racial differences now recognized as prejudiced, while Condorcet and others condemned slavery. Contemporary scholarship discusses whether such positions reveal a contradiction internal to the project, one that could then be corrected by its own principles, or a structural limit. Answers diverge, and this article limits itself to recording the debate.

Legacy

The Enlightenment left lasting marks, though their assessment is controversial:

  • Politics and law: the language of the rights of man, the separation of powers, freedom of conscience and of the press, the critique of torture and the death penalty (Beccaria, On Crimes and Punishments, 1764), present in documents such as the United States Declaration of Independence (1776) and the Declaration of the Rights of Man and of the Citizen (1789);
  • Epistemology: the idea that knowledge is a public and fallible construction subject to criticism, and the distinction between the limits and the pretensions of reason, which runs from Kant to the philosophy of science;
  • Ethics: the development of utilitarianism (from Bentham; see Utilitarianism) and of Kantian deontology;
  • The human sciences: the project of studying society with empirical methods, from Montesquieu and the Scots to Comte;
  • Secularization: the distinction between the public sphere and religious confession.

Critically, the legacy includes the very tensions this article has presented: between universalism and plurality, between critical reason and instrumental reason, between progress and the critique of progress. That is why the question of 1784 is still being asked. Each generation answers it anew, and the way of answering is itself an exercise of what Kant called the public use of reason.

Essential Readings

  • KANT, Immanuel. “Beantwortung der Frage: Was ist Aufklärung?” Berlinische Monatsschrift, December 1784. Available in English in Kant’s collected political and historical writings.
  • SCHMIDT, James (ed.). What Is Enlightenment? Eighteenth-Century Answers and Twentieth-Century Questions. Berkeley: University of California Press, 1996.
  • CASSIRER, Ernst. The Philosophy of the Enlightenment (Die Philosophie der Aufklärung, 1932).
  • GAY, Peter. The Enlightenment: An Interpretation. 2 vols. New York: Knopf, 1966–1969.
  • ISRAEL, Jonathan. Radical Enlightenment: Philosophy and the Making of Modernity, 1650–1750. Oxford: Oxford University Press, 2001.
  • OUTRAM, Dorinda. The Enlightenment. Cambridge: Cambridge University Press (several editions).
  • BERLIN, Isaiah. “The Counter-Enlightenment.” In: Dictionary of the History of Ideas, vol. 2. New York: Scribner’s, 1973; reprinted in Against the Current.
  • HORKHEIMER, Max; ADORNO, Theodor W. Dialectic of Enlightenment: Philosophical Fragments (Dialektik der Aufklärung, 1947).
  • HABERMAS, Jürgen. The Philosophical Discourse of Modernity (Der philosophische Diskurs der Moderne, 1985).
  • FOUCAULT, Michel. “What Is Enlightenment?” (1984), in Paul Rabinow (ed.), The Foucault Reader.

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