French political philosopher whose major work, The Spirit of Laws, was a major contribution to political theory.

His father, Jacques de Secondat, belonged to an old military family of modest wealth that had been ennobled in the 16th century for services to the crown, while his mother, Marie-Françoise de Pesnel, was a pious lady of partial English extraction. She brought to her husband a great increase in wealth in the valuable wine-producing property of La Brède. When she died in 1696, the barony of La Brède passed to Charles-Louis, who was her eldest child, then aged seven. Educated first at home and then in the village, he was sent away to school in 1700. The school was the Collège de Juilly, close to Paris and in the diocese of Meaux. It was much patronized by the prominent families of Bordeaux, and the priests of the Oratory, to whom it belonged, provided a sound education on enlightened and modern lines.

Charles-Louis left Juilly in 1705, continued his studies at the faculty of law at the University of Bordeaux, was graduated, and became an advocate in 1708; soon after he appears to have moved to Paris in order to obtain practical experience in law. He was called back to Bordeaux by the death of his father in 1713. Two years later he married Jeanne de Lartigue, a wealthy Protestant, who brought him a respectable dowry of 100,000 livres and in due course presented him with two daughters and a son, Jean-Baptiste. Charles-Louis admired and exploited his wife's business skill and readily left her in charge of the property on his visits to Paris. But he does not appear to have been either faithful or greatly devoted to her. In 1716 his uncle, Jean-Baptiste, baron de Montesquieu, died and left to his nephew his estates, with the barony of Montesquieu, near Agen, and the office of deputy president in the Parlement of Bordeaux. His position was one of some dignity. It carried a stipend but was no sinecure.

The young Montesquieu, at 27, was now socially and financially secure. He settled down to exercise his judicial function (engaging to this end in the minute study of Roman law), to administer his property, and to advance his knowledge of the sciences—especially of geology, biology, and physics—which he studied in the newly formed academy of Bordeaux.

In 1721 he surprised all but a few close friends by publishing his Lettres persanes (Persian Letters, 1722), in which he gave a brilliant satirical portrait of French and particularly Parisian civilization, supposedly seen through the eyes of two Persian travellers. This exceedingly successful work mocks the reign of Louis XIV, which had only recently ended; pokes fun at all social classes; discusses, in its allegorical story of the Troglodytes, the theories of Thomas Hobbes relating to the state of nature. It also makes an original, if naive, contribution to the new science of demography; continually compares Islām and Christianity; reflects the controversy about the papal bull Unigenitus, which was directed against the dissident Catholic group known as the Jansenists; satirizes Roman Catholic doctrine; and is infused throughout with a new spirit of vigorous, disrespectful, and iconoclastic criticism. The work's anonymity was soon penetrated, and Montesquieu became famous. The new ideas fermenting in Paris had received their most scintillating expression.

Montesquieu now sought to reinforce his literary achievement with social success. Going to Paris in 1722, he was assisted in entering court circles by the Duke of Berwick (Berwick-upon-Tweed, James Fitzjames, duke of, earl of Tinmouth, baron of Bosworth, duc de Fitz-James), the exiled Stuart prince whom he had known when Berwick was military governor at Bordeaux. The tone of life at court was set by the rakish regent, the Duc d'Orléans, and Montesquieu did not disdain its dissipations. It was during this period that he made the acquaintance of the English politician Viscount Bolingbroke (Bolingbroke, Henry Saint John, 1st Viscount, Baron Saint John Of Lydiard Tregoze), whose political views were later to be reflected in Montesquieu's analysis of the English constitution.

In Paris his interest in the routine activities of the Parlement in Bordeaux, however, had dwindled. He resented seeing that his intellectual inferiors were more successful than he in court. His office was marketable, and in 1726 he sold it, a move that served both to reestablish his fortunes, depleted by life in the capital, and to assist him, by lending colour to his claim to be resident in Paris, in his attempt to enter the Académie Française. A vacancy there arose in October 1727. Montesquieu had powerful supporters, with Madame de Lambert's salon firmly pressing his claims, and he was elected, taking his seat on Jan. 24, 1728.

This official recognition of his talent might have caused him to remain in Paris to enjoy it. On the contrary, though older than most noblemen starting on the grand tour, he resolved to complete his education by foreign travel. Leaving his wife at La Brède with full powers over the estate, he set off for Vienna in April 1728, with Lord Waldegrave, nephew of Berwick and lately British ambassador in Paris, as travelling companion. He wrote an account of his travels as interesting as any other of the 18th century. In Vienna he met the soldier and statesman Prince Eugene of Savoy and discussed French politics with him. He made a surprising detour into Hungary to examine the mines. He entered Italy, and, after tasting the pleasures of Venice, proceeded to visit most of the other cities. Conscientiously examining the galleries of Florence, notebook in hand, he developed his aesthetic sense. In Rome he heard the French minister Cardinal Polignac and read his unpublished Latin poem Anti-Lucretius. In Naples he skeptically witnessed the liquefaction of the blood of the city's patron saint. From Italy he moved through Germany to Holland and thence (at the end of October 1729), in the company of the statesman and wit Lord Chesterfield, to England, where he remained until the spring of 1731.

Montesquieu had a wide circle of acquaintances in England. He was presented at court, and he was received by the Prince of Wales, at whose request he later made an anthology of French songs. He became a close friend of the dukes of Richmond and Montagu. He was elected a Fellow of the Royal Society. He attended parliamentary debates and read the political journals of the day. He became a Freemason. He bought extensively for his library. His stay in England was one of the most formative periods of his life.

During his travels Montesquieu did not avoid the social pleasures that he had sought in Paris, but his serious ambitions were strengthened. He thought for a time of a diplomatic career but on his return to France decided to devote himself to literature. He hastened to La Brède and remained there, working for two years. Apart from a tiny but controversial treatise on La Monarchie universelle, printed in 1734 but at once withdrawn (so that only his own copy is extant), he was occupied with an essay on the English constitution (not published until 1748, when it became part of his major work) and with his Considérations sur les causes de la grandeur des Romains et de leur décadence (1734; Reflections on the Causes of the Grandeur and Declension of the Romans, 1734). He had thought of publishing the two together, thus following an English tradition, for, as Voltaire said, the English delighted in comparing themselves with the Romans.

Montesquieu's literary ambitions were far from exhausted. He had for some time been meditating the project of a major work on law and politics. After the publication of the Considérations, he rested for a short time and then, undismayed by failing eyesight, applied himself to this new and immense task. He undertook an extensive program of reading in law, history, economics, geography, and political theory, filling with his notes a large number of volumes, of which only one survives, Geographica, tome II. He employed a succession of secretaries, sometimes as many as six simultaneously, using them as readers and as amanuenses, but not as précis writers. An effort of this magnitude was entirely foreign to what was publicly known of his character, for he was generally looked on as brilliant, rapid, and superficial. He did not seek to disabuse the world at large. Only a small number of friends knew what he was engaged in. He worked much at La Brède, devoting himself also to the administration of his estates and to the maintenance of his privileges as a landed proprietor. But he continued to visit Paris and to enjoy its social life. He kept there a second library and also made use of the Bibliothèque du Roi. He attended the Académie, visited the salons, and enjoyed meeting Italian and English visitors. At the same time he persistently, unostentatiously pressed on with the preparation of the book that he knew would be a masterpiece. By 1740 its main lines were established and a great part of it was written. By 1743 the text was virtually complete, and he began the first of two thorough and detailed revisions, which occupied him until December 1746. The actual preparation for the press was at hand. A Geneva publisher, J. Barrillot, was selected, further corrections were made, several new chapters were written and in November 1748 the work appeared under the title De l'esprit des loix, ou du rapport que les loix doivent avoir avec la constitution de chaque gouvernement, les moeurs, le climat, la religion, le commerce, etc. (The Spirit of Laws, 1750). It consisted of two quarto volumes, comprising 31 books in 1,086 pages.

L'Esprit des lois is one of the great works in the history of political theory and in the history of jurisprudence. Its author had acquainted himself with all previous schools of thought but identified himself with none. Of the multiplicity of subjects treated by Montesquieu, none remained unadorned. His treatment of three was particularly memorable.

The first of these is his classification of governments, a subject that was de rigueur for a political theorist (political science). Abandoning the classical divisions of his predecessors into monarchy, aristocracy, and democracy, Montesquieu produced his own analysis and assigned to each form of government an animating principle: the republic, based on virtue; the monarchy, based on honour; and despotism, based on fear. His definitions show that this classification rests not on the location of political power but on the government's manner of conducting policy; it involves a historical and not a narrow descriptive approach.

The second of his most noted arguments, the theory of the separation of powers (powers, separation of), is treated differently. Dividing political authority (constitutional law) into the legislative, executive, and judicial powers, he asserted that, in the state that most effectively promotes liberty, these three powers must be confided to different individuals or bodies, acting independently. His model of such a state was England, which he saw from the point of view of the Tory opposition to the Whig leader, Robert Walpole, as expressed in Bolingbroke's polemical writings. The chapter in which he expressed this doctrine—book xi, chapter 6, the most famous of the entire book—had lain in his drawers, save for revision or correction, since it was penned in 1734. It at once became perhaps the most important piece of political writing of the 18th century. Though its accuracy has in more recent times been disputed, in its own century it was admired and held authoritative, even in England; it inspired the Declaration of the Rights of Man (Declaration of the Rights of Man and of the Citizen) and the Constitution of the United States. (Constitution of the United States of America)

The third of Montesquieu's most celebrated doctrines is that of the political influence of climate. Basing himself on doctrines met in his reading, on the experience of his travels, and on experiments—admittedly somewhat naive—conducted at Bordeaux, he stressed the effect of climate, primarily thinking of heat and cold, on the physical frame of the individual, and, as a consequence, on the intellectual outlook of society. This influence, he claims, is not, save in primitive societies, insuperable. It is the legislator's duty to counteract it. Montesquieu took care (as his critics have not always realized) to insist that climate is but one of many factors in an assembly of secondary causes that he called the “general spirit.” The other factors (laws, religion, and maxims of government being the most important) are of a nonphysical nature, and their influence, compared with that of climate, grows as civilization advances.

Society for Montesquieu must be considered as a whole. Religion itself is a social phenomenon, whether considered as a cause or as an effect, and the utility or harmfulness of any faith can be discussed in complete independence of the truth of its doctrines. Here and elsewhere, undogmatic observation was Montesquieu's preferred method. Sometimes the reader is beguiled by this into the belief that Montesquieu maintains that whatever exists, though it may indeed stand in need of improvement, cannot be wholly bad. Although with a bold parenthesis or a rapid summing-up the reader is reminded that for Montesquieu certain things are intrinsically evil: despotism, slavery, intolerance. Though he never attempted an enumeration of the rights of man and would probably have disapproved of such an attempt, he maintained a firm belief in human dignity.

In the final books of L'Esprit des lois, added at the last moment and imperfectly assimilated to the rest, he addressed himself to the history of law (law, philosophy of), seeking to explain the division of France into the two zones of written and customary law, and made his contribution to the much discussed controversy about the origins of the French aristocracy. Here he displays not only prudence and common sense, but also a real scholarly capacity, which he had not shown before, for the philological handling of textual evidence.

After the book was published, praise came to Montesquieu from the most varied headquarters. The Scottish philosopher David Hume (Hume, David) wrote from London that the work would win the admiration of all the ages; an Italian friend spoke of reading it in an ecstasy of admiration; the Swiss scientist Charles Bonnet (Bonnet, Charles) said that Montesquieu had discovered the laws of the intellectual world as Newton had those of the physical world. The philosophers (philosophe) of the Enlightenment accepted him as one of their own, as indeed he was. The work was controversial, however, and a variety of denunciatory articles amd pamphlets appeared. Attacks made in the Sorbonne and in the general assembly of the French clergy were deflected, but in Rome, in spite of the intervention of the French ambassador and of several liberal-minded high ecclesiastics and notwithstanding the favourable disposition of the Pope himself, Montesquieu's enemies were successful, and the work was placed on the Index Librorum Prohibitorum in 1751. This, though it dismayed Montesquieu, was but a momentary setback. He had already published his Défense de L'Esprit des lois (1750). Subtle and good-humoured, but forceful and incisive, this was the most brilliantly written of all his works. His fame was now worldwide.

Renown lay lightly on his shoulders. His affability and modesty are commented on by all who met him. He was a faithful friend, kind and helpful to young and unestablished men of letters, witty, though absent-minded, in society. It was to be expected that the editors of the Encyclopédie should wish to have his collaboration, and d'Alembert asked him to write on democracy and despotism. Montesquieu declined, saying that he had already had his say on those themes but would like to write on taste. The resultant Essai sur le goût (Essay on Taste), first drafted about 25 years earlier, was his last work.