• Historian and Sociologist Ibn Khaldun, 1332
• Political Philosopher Charles - Louis de Secondat, baron de La Brède et de Montesquieu, 1689

He is best known for his Muqaddimah (known as Prolegomenon in English), which was discovered, evaluated and fully appreciated first by 19th century European scholarship, although it has also had considerable influence on 17th century Ottoman historians like Ḥajjī Khalīfa and Mustafa Naima who relied on his theories to analyze the growth and decline of the Ottoman empire. Later in the 19th century, Western scholars recognized him as one of the greatest philosophers to come out of the Muslim world.

Ibn Khaldun's life is relatively well documented, as he wrote an autobiography (التعريف بابن خلدون ورحلته غربا وشرقا; Al-Taʻrīf bi Ibn-Khaldūn wa Riħlatuhu Gharbān wa Sharqān) in which numerous documents regarding his life are quoted word - for - word. However, the autobiography has little to say about his private life, so little is known about his family background. Generally known as "Ibn Khaldūn" after a remote ancestor, he was born in Tunis in AD 1332 (732 A.H.) into an upper class Andalusian family, the Banū Khaldūn. His family, which held many high offices in Andalusia, had emigrated to Tunisia after the fall of Sevilla to Reconquista forces around the middle of the 13th century. Under the Tunisian Hafsid dynasty some of his family held political office; Ibn Khaldūn's father and grandfather however withdrew from political life and joined a mystical order. His brother, Yahya Ibn Khaldun, was also a historian who wrote a book on the Abdalwadid dynasty, and who was assassinated by a rival for being the official historiographer of the court.

In his autobiography, Ibn Khaldun traces his descent back to the time of Muhammad through an Arab tribe from Yemen, specifically Hadhramaut, which came to Spain in the eighth century at the beginning of the Islamic conquest. In his own words: "And our ancestry is from Hadhramaut, from the Arabs of Yemen, via Wa'il ibn Hajar, from the best of the Arabs, well known and respected." However, the biographer Mohammad Enan questions his claim, suggesting that his family may have been Muladis who pretended to be of Arab origin in order to gain social status. Enan also mentions a well documented past tradition, concerning certain Berber groups, whereby they delusively "aggrandize" themselves with some Arab ancestry. The motive of such an invention was always the desire for political and societal ascendancy. Some speculate this of the Khaldun family; they elaborate that Ibn Khaldun himself was the product of the same Berber ancestry as the native majority of his birthplace. A point congenial to this posits that Ibn Khaldun's unusual written focus on, and admiration for Berbers reveals a deference towards them that is born of a vested interest in preserving them in the realm of conscious history; such is that which the true Arabs of his day would find no enthusiasm for and indeed a vested interest in suppressing. Moreover the special position that he affords Berbers in his work is fully vindicated upon comparing it with his vitriolic attitudes towards the Arab, and his relative disinterest in the state of affairs outside the Maghreb. In contrast, Muhammad Hozien chooses to believe: "The false [Berber] identity would be valid however at the time that Ibn Khaldun’s ancestors left Andalusia and moved to Tunisia they did not change their claim to Arab ancestry. Even in the times when Berbers were ruling in Al-Andalus, the reigns of Almoravids and Almohads, the Ibn Khalduns did not reclaim their Berber heritage." This point ignores the aforementioned phenomenon of adopting an Arab ancestry to garner prestige.

His family's high rank enabled Ibn Khaldun to study with the best teachers in Maghreb. He received a classical Islamic education, studying the Qur'an which he memorized by heart, Arabic linguistics, the basis for an understanding of the Qur'an, hadith, sharia (law) and fiqh (jurisprudence). He received certification (ijazah) for all these subjects. The mystic, mathematician and philosopher, Al-Abili of Tlemcen, introduced him to mathematics, logic and philosophy, where he above all studied the works of Averroes, Avicenna, Razi and Tusi. At the age of 17, Ibn Khaldūn lost both his parents to the Black Death, an intercontinental epidemic of the plague that hit Tunis in 1348 – 1349.

Following family tradition, Ibn Khaldūn strove for a political career. In the face of a tumultuous political situation in North Africa, this required a high degree of skill developing and dropping alliances prudently, to avoid falling with the short lived regimes of the time. Ibn Khaldūn's autobiography is the story of an adventure, in which he spends time in prison, reaches the highest offices and falls again into exile.

At the age of 20, he began his political career at the Chancellery of the Tunisian ruler Ibn Tafrakin with the position of Kātib al-'Alāmah, which consisted of writing in fine calligraphy the typical introductory notes of official documents. In 1352, Abū Ziad, the Sultan of Constantine, marched on Tunis and defeated it. Ibn Khaldūn, in any case unhappy with his respected but politically meaningless position, followed his teacher Abili to Fez. Here the Marinid sultan Abū Inan Fares I appointed him as a writer of royal proclamations, which did not prevent Ibn Khaldūn from scheming against his employer. In 1357 this brought the 25 year old a 22 month prison sentence. Upon the death of Abū Inan in 1358, the vizier al-Hasān ibn-Umar granted him freedom and reinstated him in his rank and offices. Ibn Khaldūn then schemed against Abū Inan's successor, Abū Salem Ibrahim III, with Abū Salem's exiled uncle, Abū Salem. When Abū Salem came to power, he gave Ibn Khaldūn a ministerial position, the first position which corresponded with Ibn Khaldūn's ambitions.

The treatment Ibn Khaldun received after the fall of Abū Salem through Ibn-Amar ʻAbdullah, a friend of Ibn Khaldūn's, was not to his liking, he received no significant official position. At the same time, Amar successfully prevented Ibn Khaldūn – whose political skills he was well aware of – from allying with the Abd al-Wadids in Tlemcen. Ibn Khaldūn therefore decided to move to Granada. He could be sure of a positive welcome there, since at Fez he had helped the Sultan of Granada, the Nasrid Muhammad V, regain power from his temporary exile. In 1364 Muhammad entrusted him with a diplomatic mission to the King of Castilla, Pedro the Cruel, to endorse a peace treaty. Ibn Khaldūn successfully carried out this mission, and politely declined Pedro's offer to remain at his court and have his family's Spanish possessions returned to him.

In Granada, Ibn Khaldūn quickly came into competition with Muhammad's vizier, Ibn al-Khatib, who saw the close relationship between Muhammad and Ibn Khaldūn with increasing mistrust. Ibn Khaldūn tried to shape the young Muhammad into his ideal of a wise ruler, an enterprise which Ibn al-Khatib thought foolish and a danger to peace in the country – and history proved him right. At al-Khatib's instigation, Ibn Khaldūn was eventually sent back to North Africa. Al-Khatib himself was later accused by Muhammad of having unorthodox philosophical views, and murdered, despite an attempt by Ibn Khaldūn to intercede on behalf of his old rival.

In his autobiography, Ibn Khaldūn tells us little about his conflict with Ibn al-Khatib and the reasons for his departure. The orientalist Muhsin Mahdi interprets this as showing that Ibn Khaldūn later realized that he had completely misjudged Muhammad V.

Back in Africa, the Hafsid sultan of Bougie, Abū ʻAbdallāh, (who had been his companion in prison) received him with great enthusiasm, and made Ibn Khaldūn his prime minister. During this period, Ibn Khaldūn carried out a daring mission to collect taxes among the local Berber tribes. After the death of Abū ʻAbdallāh in 1366, Ibn Khaldūn changed sides once again and allied himself with the ruler of Tlemcen, Abū l-Abbas. A few years later he was taken prisoner by ʻAbdu l-Azīz, who had defeated the sultan of Tlemcen and seized the throne. He then entered a monastic establishment, and occupied himself with scholastic duties, until in 1370 he was sent for to Tlemcen by the new sultan. After the death of ʻAbdu l-Azīz, he resided at Fez, enjoying the patronage and confidence of the regent.

Ibn Khaldūn's political skills, above all his good relationship with the wild Berber tribes, were in high demand among the North African rulers, whereas he himself began to tire of politics and constant switching of allegiances. In 1375, sent by Abū Hammu, the ʻAbdu l Wadid Sultan of Tlemcen, on a mission to the Dawadida Arabs tribes of Biskra. Thereafter Ibn Khaldūn returns to the West sought refuge with one of the Berber tribes, in the west of Algeria, in the town of Qalat Ibn Salama. He lived there for over three years under their protection, taking advantage of his seclusion to write the Muqaddimah "Prolegomena", the introduction to his planned history of the world. In Ibn Salama, however, he lacked the necessary texts to complete the work. As a result, in 1378, he returned to his native Tunis, which in the mean time had been conquered by Abū l-Abbas, who took Ibn Khaldūn back into his service. There he devoted himself almost exclusively to his studies and completed his history of the world. His relationship with Abū l-Abbas remained strained, as the latter questioned his loyalty. This was brought into sharp contrast after Ibn Khaldūn presented him with a copy of the completed history omitting the usual panegyric to the ruler. Under pretense of going on the Hajj to Mecca – something a Muslim ruler could not simply refuse permission for – Ibn Khaldūn was able to leave Tunis and sail to Alexandria.

Ibn Khaldun said of Egypt, "He who has not seen it does not know the power of Islam." While other Islamic regions had to cope with border wars and inner strife, under the Mamluks Egypt experienced a period of economic prosperity and high culture. However, even in Egypt, where Ibn Khaldūn lived out his days, he could not stay out of politics completely. In 1384 the Egyptian Sultan, al-Malik udh-Dhahir Barquq, made him Professor of the Qamhiyyah Madrasah, and grand Qadi of the Maliki school of fiqh (one of four schools, the Maliki school was widespread primarily in West Africa). His efforts at reform encountered resistance, however, and within a year he had to resign his judgeship. A contributory factor to his decision to resign may have been the heavy personal blow that struck him in 1384, when a ship carrying his wife and children sank off the coast of Alexandria. Ibn Khaldun now decided to complete the pilgrimage to Mecca after all.

After his return in May 1388, Ibn Khaldūn concentrated more strongly on a purely educational function at various Cairo madrasas. At court he fell out of favor for a time, as during revolts against Barquq he had – apparently under duress – together with other Cairo jurists issued a Fatwa against Barquq. Later relations with Barquq returned to normal, and he was once again named the Maliki qadi. Altogether he was called six times to this high office, which for various reasons he never held long.

In 1401, under Barquq's successor, his son Faraj, Ibn Khaldūn took part in a military campaign against the Mongol conqueror Timur, who besieged Damascus. Ibn Khaldūn cast doubt upon the viability of the venture and didn't really want to leave Egypt. His doubts were vindicated, as the young and inexperienced Faraj, concerned about a revolt in Egypt, left his army to its own devices in Syria and hurried home. Ibn Khaldūn remained at the besieged city for seven weeks, being lowered over the city wall by ropes in order to negotiate with Timur, in a historic series of meetings which he reports extensively in his autobiography. Timur questioned him in detail about conditions in the lands of the Maghreb; at his request, Ibn Khaldūn even wrote a long report about it. As he recognized the intentions behind this, he did not hesitate, on his return to Egypt, to compose an equally extensive report on the history of the Tartars, together with a character study of Timur, sending these to the Merinid rulers in Fez (Maghreb).

Ibn Khaldūn spent the following five years in Cairo completing his autobiography and his history of the world and acting as teacher and judge. During this time he is alleged to have joined an underground party named Rijal Hawa Rijal. Their reform oriented ideals attracted the attention of local political authorities and the elderly Ibn Khaldun was placed under arrest. He died on 19 March 1406, one month after his sixth selection for the office of the Maliki qadi (Judge).

Ibn Khaldūn has left behind few works other than his history of the world, al-Kitābu l-ʻibār. Significantly, such writings are not alluded to in his autobiography, suggesting perhaps that Ibn Khaldūn saw himself first and foremost as a historian and wanted to be known above all as the author of al-Kitābu l-ʻibār. From other sources we know of several other works, primarily composed during the time he spent in North Africa and Al-Andalus. His first book, Lubābu l-Muhassal, a commentary on the Islamic theology of Fakhr al-Din al-Razi, was written at the age of 19 under the supervision of his teacher al-Ābilī in Tunis. A work on Sufism, Sifā'u l-Sā'il, was composed around 1373 in Fes, Morocco. Whilst at the court of Muhammed V, Sultan of Granada, Ibn Khaldūn composed a work on logic, ʻallaqa li-l-Sultān.

The Kitābu l-ʻibār (full title: Kitābu l-ʻibār wa Diwānu l-Mubtada' wa l-Ħabar fī tarikhi l-ʻarab wa l-Barbar wa man ʻĀsarahum min Đawī Ash-Sha'n l-Akbār "Book of lessons, Record of Beginnings and Events in the history of the Arabs and Berbers and their Powerful Contemporaries"), Ibn Khaldūn's main work, was originally conceived as a history of the Berbers. Later, the focus was widened so that in its final form (including its own methodology and anthropology), to represent a so-called "universal history". It is divided into seven books, the first of which, the Muqaddimah, can be considered a separate work. Books two to five cover the history of mankind up to the time of Ibn Khaldūn. Books six and seven cover the history of the Berber peoples and the Maghreb, which remain invaluable to present day historians, as they are based on Ibn Khaldūn's personal knowledge of the Berbers.

Concerning the discipline of sociology, he conceived a theory of social conflict. He developed the dichotomy of sedentary life versus nomadic life as well as the concept of a "generation," and the inevitable loss of power that occurs when desert warriors conquer a city. Following a contemporary Arab scholar, Sati' al-Husri, the Muqaddimah may be read as a sociological work: six books of general sociology. Topics dealt with in this work include politics, urban life, economics and knowledge. The work is based around Ibn Khaldun's central concept of 'asabiyyah, which has been translated as "social cohesion", "group solidarity", or "tribalism". This social cohesion arises spontaneously in tribes and other small kinship groups; it can be intensified and enlarged by a religious ideology. Ibn Khaldun's analysis looks at how this cohesion carries groups to power but contains within itself the seeds – psychological, sociological, economic, political – of the group's downfall, to be replaced by a new group, dynasty or empire bound by a stronger (or at least younger and more vigorous) cohesion. Ibn Khaldun has been cited as a racist, but his theories on the rise and fall of empires had no racial component, and this reading of his work has been claimed to be the result of mistranslations.

Perhaps the most frequently cited observation drawn from Ibn Khaldūn's work is the notion that when a society becomes a great civilization (and, presumably, the dominant culture in its region), its high point is followed by a period of decay. This means that the next cohesive group that conquers the diminished civilization is, by comparison, a group of barbarians. Once the barbarians solidify their control over the conquered society, however, they become attracted to its more refined aspects, such as literacy and arts, and either assimilate into or appropriate such cultural practices. Then, eventually, the former barbarians will be conquered by a new set of barbarians, who will repeat the process. Some contemporary readers of Khaldun have read this as an early business cycle theory, though set in the historical circumstances of the mature Islamic empire.

Ibn Khaldun's outlines an early (possibly even the earliest) example of political economy. He describes the economy as being composed of value adding processes; that is, labor and skill is added to techniques and crafts and the product is sold at a higher value. He also made the distinction between "profit" and "sustenance", in modern political economy terms, surplus and that required for the reproduction of classes respectively. He also calls for the creation of a science to explain society and goes on to outline these ideas in his major work the Muqaddimah.

Ibn Khaldun was also known for his work Tahrir al Ahkam fi Tadbeer ahl al Islam, which is concerned with questions of political legitimacy in Islamic societies.

Ibn Khaldun was first brought to the attention of the Western world in 1697, when a biography of him appeared in Barthélemy d'Herbelot de Molainville's Bibliothèque Orientale. Ibn Khaldun began gaining more attention from 1806, when Silvestre de Sacy's Chrestomathie Arabe included his biography together with a translation of parts of the Muqaddimah as the Prolegomena. In 1816, de Sacy again published a biography with a more detailed description on the Prolegomena. More details on and partial translations of the Prolegomena emerged over the years until the complete Arabic edition was published in 1858, followed by a complete French translation a few years later by de Sacy. Since then, the work of Ibn Khaldun has been extensively studied in the Western world with special interest.

• British historian Arnold J. Toynbee called the Muqaddimah "a philosophy of history which is undoubtedly the greatest work of its kind that has ever yet been created by any mind in any time or place."

• The British philosopher Robert Flint wrote the following on Ibn Khaldun: "...as a theorist of history he had no equal in any age or country until Vico appeared, more than three hundred years later. Plato, Aristotle and Augustine were not his peers, and all others were unworthy of being even mentioned along with him".

• Abderrahmane Lakhsassi writes: "No historian of the Maghreb since and particularly of the Berbers can do without his historical contribution."

• The British philosopher - anthropologist Ernest Gellner considered Ibn Khaldun's definition of government, "an institution which prevents injustice other than such as it commits itself", the best in the history of political theory.

• Egon Orowan, who termed the concept of socionomy, was influenced by Ibn Khaldun's ideas on the evolution of societies.

• Arthur Laffer, whom the Laffer curve is named after, noted that, among others, some of Ibn Khaldun's ideas precede his own.

• In 2004, the Tunisian Community Center launched the first Ibn Khaldun award for the Tunisian American Student of the Year, as an honor to Ibn Khaldun's contribution in Tunisia.

• In 2006, the Atlas Economic Research Foundation launched an annual essay contest for Muslim students named in Ibn Khaldun's honor. The theme of the contest is "how individuals, think tanks, universities and entrepreneurs can influence government policies to allow the free market to flourish and improve the lives of its citizens based on Islamic teachings and traditions."

• In 2006, Spain commemorated the 600th anniversary of the death of Ibn Khaldun.

He was born at the Château de la Brède in the southwest of France. His father, Jacques de Secondat, was a soldier with a long noble ancestry. His mother, Marie Françoise de Pesnel who died when Charles de Secondat was seven, was a female inheritor of a large monetary inheritance who brought the title of barony of La Brède to the Secondat family. After having studied at the Catholic College of Juilly, Charles - Louis de Secondat married. His wife, Jeanne de Lartigue, a Protestant, brought him a substantial dowry when he was 26. The next year, he inherited a fortune upon the death of his uncle, as well as the title Baron de Montesquieu and Président à Mortier in the Parliament of Bordeaux. By that time, England had declared itself a constitutional monarchy in the wake of its Glorious Revolution (1688 – 89), and had joined with Scotland in the Union of 1707 to form the Kingdom of Great Britain. In 1715 the long reigning Louis XIV died and was succeeded by the five year old Louis XV. These national transformations impacted Montesquieu greatly; he would later refer to them repeatedly in his work.

Soon afterwards, he achieved literary success with the publication of his Lettres persanes (Persian Letters, 1721), a satire based on the imaginary correspondence of a Persian visitor to Paris, pointing out the absurdities of contemporary society. He next published Considérations sur les causes de la grandeur des Romains et de leur décadence (Considerations on the Causes of the Grandeur and Decadence of the Romans, 1734), considered by some scholars a transition from The Persian Letters to his master work. De l'Esprit des Lois (The Spirit of the Laws) was originally published anonymously in 1748 and quickly rose to a position of enormous influence. In France, it met with an unfriendly reception from both supporters and opponents of the regime. The Catholic Church banned l'Esprit – along with many of Montesquieu's other works – in 1751 and included it on the Index of Prohibited Books. It received the highest praise from the rest of Europe, especially Britain.

Montesquieu was also highly regarded in the British colonies in North America as a champion of British liberty (though not of American independence). Political scientist Donald Lutz found that Montesquieu was the most frequently quoted authority on government and politics in colonial pre - revolutionary British America, cited more by the American founders than any source except for the Bible. Following the American revolution, Montesquieu's work remained a powerful influence on many of the American founders, most notably James Madison of Virginia, the "Father of the Constitution". Montesquieu's philosophy that "government should be set up so that no man need be afraid of another" reminded Madison and others that a free and stable foundation for their new national government required a clearly defined and balanced separation of powers.

Besides composing additional works on society and politics, Montesquieu traveled for a number of years through Europe including Austria and Hungary, spending a year in Italy and 18 months in England before resettling in France. He was troubled by poor eyesight, and was completely blind by the time he died from a high fever in 1755. He was buried in the Église Saint - Sulpice, Paris.

Montesquieu's philosophy of history minimized the role of individual persons and events. He expounded the view in Considérations sur les causes de la grandeur des Romains et de leur décadence that each historical event was driven by a principal movement:

It is not chance that rules the world. Ask the Romans, who had a continuous sequence of successes when they were guided by a certain plan, and an uninterrupted sequence of reverses when they followed another. There are general causes, moral and physical, which act in every monarchy, elevating it, maintaining it, or hurling it to the ground. All accidents are controlled by these causes. And if the chance of one battle — that is, a particular cause — has brought a state to ruin, some general cause made it necessary for that state to perish from a single battle. In a word, the main trend draws with it all particular accidents.

In discussing the transition from the Republic to the Empire, he suggested that if Caesar and Pompey had not worked to usurp the government of the Republic, other men would have risen in their place. The cause was not the ambition of Caesar or Pompey, but the ambition of man.

Montesquieu is credited amongst the precursors of anthropology, including Herodotus and Tacitus, to be among the first to extend comparative methods of classification to the political forms in human societies. Indeed, the French political anthropologist Georges Balandier considered Montesquieu to be "the initiator of a scientific enterprise that for a time performed the role of cultural and social anthropology". According to social anthropologist D. F. Pocock, Montesquieu's 'On the Spirit of Laws' "is the first consistent attempt to survey the varieties of human society, to classify and compare them and, within society, to study the inter - functioning of institutions". Montesquieu's political anthropology gave rise to his theories on government.

Montesquieu's most influential work divided French society into three classes (or trias politica, a term he coined): the monarchy, the aristocracy and the commons. Montesquieu saw two types of governmental power existing: the sovereign and the administrative. The administrative powers were the executive, the legislative, and the judicial. These should be separate from and dependent upon each other so that the influence of any one power would not be able to exceed that of the other two, either singly or in combination. This was a radical idea because it completely eliminated the three Estates structure of the French Monarchy: the clergy, the aristocracy, and the people at large represented by the Estates - General, thereby erasing the last vestige of a feudalistic structure.

Likewise, there were three main forms of government, each supported by a social "principle": monarchies (free governments headed by a hereditary figure, e.g. king, queen, emperor), which rely on the principle of honor; republics (free governments headed by popularly elected leaders), which rely on the principle of virtue; and despotisms (enslaved governments headed by dictators), which rely on fear. The free governments are dependent on fragile constitutional arrangements. Montesquieu devotes four chapters of The Spirit of the Laws to a discussion of England, a contemporary free government, where liberty was sustained by a balance of powers. Montesquieu worried that in France the intermediate powers (i.e., the nobility) which moderated the power of the prince were being eroded. These ideas of the control of power were often used in the thinking of Maximilien de Robespierre.

Montesquieu was somewhat ahead of his time in advocating major reform of slavery in The Spirit of the Laws. As part of his advocacy he presented a satirical hypothetical list of arguments for slavery, which has been open to contextomy. However, like many of his generation, Montesquieu also held a number of views that might today be judged controversial. He firmly accepted the role of a hereditary aristocracy and the value of primogeniture, and while he endorsed the idea that a woman could head a state, he held that she could not be effective as the head of a family.

Another example of Montesquieu's anthropological thinking, outlined in The Spirit of the Laws and hinted at in Persian Letters, is his meteorological climate theory, which holds that climate may substantially influence the nature of man and his society. By placing an emphasis on environmental influences as a material condition of life, Montesquieu prefigured modern anthropology's concern with the impact of material conditions, such as available energy sources, organized production systems and technologies, on the growth of complex socio - cultural systems.

He goes so far as to assert that certain climates are superior to others, the temperate climate of France being ideal. His view is that people living in very warm countries are "too hot - tempered," while those in northern countries are "icy" or "stiff." The climate of middle Europe is therefore optimal. On this point, Montesquieu may well have been influenced by a similar pronouncement in The Histories of Herodotus, where he makes a distinction between the 'ideal' temperate climate of Greece as opposed to the overly cold climate of Scythia and the overly warm climate of Egypt. This was a common belief at the time, and can also be found within the medical writings of Herodotus' times, including the 'On Airs, Waters, Places' of the Hippocratic corpus. One can find a similar statement in Germania by Tacitus, one of Montesquieu's favorite authors. However, the earlier works that most closely resemble Montesquieu's complex climate theory are the Muqaddimah (1377) by the Arab sociologist, Ibn Khaldun, and The Travels of Sir John Chardin in Persia and the Orient (1711) by the French traveler Jean Chardin.

From a sociological perspective Louis Althusser, in his analysis of Montesquieu's revolution in method, alluded to the seminal character of anthropology's inclusion of material factors, such as climate, in the explanation of social dynamics and political forms. Examples of certain climatic and geographical factors giving rise to increasingly complex social systems include those that were conducive to the rise of agriculture and the domestication of wild plants and animals.