Primogeniture is the right, by law or custom, of the firstborn son to inherit the entire estate, to the exclusion of younger siblings (compare to ultimogeniture). Historically, the term implied male primogeniture, to the exclusion of females. In the absence of children, inheritance passed to collateral relatives, in order of seniority of their lines of descent. The eligible descendants of deceased elder siblings take precedence over living younger siblings, such that inheritance is settled in the manner of a depth-first search.
The principle has applied in history to inheritance of real property (land) and inherited titles and offices, most notably monarchies, continuing until modified or abolished .
Variations on primogeniture modify the right of the first-born son to the entirety of a family's inheritance (see appanage) or, in the West since World War II with the wider promotion of feminism, eliminate the preference for male over female siblings. Six monarchies in Europe have eliminated male preference: Sweden, Norway, Netherlands, Belgium, Denmark and Luxembourg. The type of marriage prevalent in each culture plays a crucial role in the adoption of differing primogenitures.
Absolute cognatic primogeniture 
Absolute, equal or lineal primogeniture, known in French as aînesse intégrale (integral primogeniture), is inheritance by the oldest surviving child without regard to gender. It is also known as (full) cognatic primogeniture today. This form of primogeniture was not practiced by any modern monarchy before 1980.
However, according to Poumarede (1972), the Basques of the Kingdom of Navarre transmitted title and property to the first-born, whatever the gender. This inheritance practice was followed by the high nobility and free families alike in the early and high middle ages. The Navarrese monarchy had been inherited by dynasties from outside of Navarre, which followed different succession laws (usually male preference primogeniture. Aînesse intégrale practices weakened among the high nobility of Navarre once Navarre became more exposed to and pressured by outside influences, and largely disappeared from use by the high nobility once the Kingdom of Navarre was merged with the French crown when it followed Salic Law. Eventually only the Basque gentry and free families of the Basque Country and other regions continued to follow this practice, which persisted as late as the 19th century.
In 1980 Sweden revised its constitution to adopt royal succession by absolute primogeniture, displacing King Carl XVI Gustaf's infant son, Carl Philip, in favor of his elder daughter, Victoria, in the process. Several other monarchies have since followed suit: the Netherlands in 1983, Norway in 1990, Belgium in 1991, Denmark (see below) in 2009, and Luxembourg in 2011.
Recently other countries have changed or have considered changing to absolute primogeniture:
- In July 2006, the Nepalese government proposed adopting equal primogeniture, but the monarchy was abolished 28 May 2008.
- In Japan, debates have occurred over whether to adopt absolute primogeniture, as Princess Aiko is the only child of Crown Prince Naruhito. But, the birth of Prince Hisahito, a son of Prince Akishino (younger brother of Crown Prince Naruhito, and next in line to the Chrysanthemum Throne after Naruhito) has side-lined the debate.
- In the United Kingdom, the Succession to the Crown Bill of 2004 proposed changing the line of succession to the British throne to absolute primogeniture. The same proposal is part of the Equality Bill announced in 2008. Shortly after the announcement, the Attorney General said there were "no immediate plans to legislate" on that part of the bill; One of the reasons to delay was the difficulty in gaining approval for the change in the 15 other Commonwealth realms. In 2011 the governments of the Commonwealth realms announced plans to legislate changes to gender-equal primogeniture.
- In 2006 and 2009, the Danish parliament voted almost unanimously, with two abstentions, in favour of a new royal succession law that would allow a first-born child to ascend the throne. This was approved by a referendum held on 7 June 2009.
- In 2006, King Juan Carlos I of Spain issued a decree reforming the succession to noble titles from male preference primogeniture to absolute cognatic primogeniture, where the first born inherits title regardless of gender.
"'The order of succession for all noble dignitaries is determined in accordance with the title of concession and, if there is none, with that traditionally applied in these cases. When the order of succession to the title is not specified in the nobility title creation charter, the following rules apply.":
- "Absolute preference is given to the direct descending line over the collateral and ascending line, and, within the same line, the closest degree takes precedence over the more remote and, within the same degree, the elder over the younger, combined with the principles of first-born and representation."
- "Men and women have an equal right of succession in Grandee of Spain and nobility titles, and no person may be given preference in the normal order of succession for reasons of gender".
A variation of this system allows women to succeed, as long as their offspring does not, in order to keep the throne in the family. Such were the cases of the few Empresses of Japan. In Norway, a nuance on this system excludes every member of the family who is not a descendant of the last monarch.
The motivation behind this system is recent and based on some views of equality between men and women. An ancient and alternative way in which women managed to rise to power, especially without displacing the direct male line descendants of the first monarchs, is the historical Consortium or Coregency between husband and wife or other relatives. The most notable of these are the Egyptian cases of Hatshepsut and Thutmose III, as well as the Ptolemaic Dynasty's Kings and Queens.
Agnatic primogeniture 
One's agnate may be male or female provided that the kinship is calculated patrilineally; i.e., only through males back to a common ancestor. "Agnatic primogeniture" or "patrilineal primogeniture" is inheritance according to seniority of birth among the sons of a monarch or head of family, with sons and their male issue inheriting before brothers and their issue. Thus, inheritance could be traced through the male line only, to the complete exclusion of females. This is commonly referred to as the Salic law (see Terra salica).
By the beginning of the 19th century, only the royal houses of Bourbon and Savoy, among Europe's historic national dynasties, continued to exclude women from succession. Later, the new monarchies or dynasties of France (under the Bonapartes), Belgium, Denmark (from 1853), Sweden (from 1810), and the Balkan realms of Albania, Bulgaria, Montenegro, Romania, and Serbia introduced Salic law. During this era, Spain and Portugal fought civil wars which pitted the Salic and female-line heirs of their dynasties against one another for possession of the crown.
A variation on Salic primogeniture allows the sons of women to inherit, but not women themselves, an example being succession to the throne of Spain from 1947–1978. This is the law in Liechtenstein and in the former Archduchy of Austria.
Semi-Salic laws 
Another variation is the so-called semi-Salic Law, which allows women to succeed only at the extinction of all the male descendants in the male line. Such were the cases of Bourbon Spain until 1833 and the dominions of Austria-Hungary, as well as most realms within the former Holy Roman Empire, i.e. most German monarchies. This was also the law of Luxembourg until equal primogeniture was introduced on 20 June 2011.
"Agnatic-cognatic primogeniture" allows female agnates (or their descendants) to inherit once there are no surviving male agnates. The term semi-Salic succession is used in the same meaning. Usually, women do not succeed by application of the same kind of primogeniture as was in effect among males in the family. Rather, the female who is nearest in kinship to the last male monarch of the family inherits, even if another female agnate of the dynasty is senior by primogeniture. Among sisters (and the lines of descendants issuing from them), the elder are preferred to the younger. In reckoning consanguinity or proximity of blood the law defines who among female relatives is "nearest" to the last male. Definitions varied among monarchies where semi-Salic succession was prevalent.
Male-preference cognatic primogeniture 
Male-preference cognatic primogeniture or mixed-gender succession allow a female to succeed if she has no living brothers and no deceased brothers who left surviving legitimate descendants. A person is always immediately followed in the succession by his or her own legitimate descendants (his or her line) except for any legitimate descendants who already appear higher in the line of succession. A person's sons and their lines all come before a person's daughters and their lines. Older sons and their lines come before younger sons and their lines. Older daughters and their lines come before younger daughters and their lines.
This was the most common primogeniture practiced in Western European feudalism, such as the Castilian Siete Partidas. Male-preferred primogeniture is currently practised in Monaco, Spain, Thailand and the sixteen Commonwealth Realms. It also used to be practised in Portugal and in Brazil. It is usually the rule for Scotland and baronies by writ in the United Kingdom; although baronies by writ go into abeyance if there are several surviving sisters or their legitimate descendants.
The Spanish Constitution of 1978 codifies an example of male preference primogeniture as it has been traditionally practiced in Spain.
The Crown of Spain shall be inherited by the successors of H.M. Juan Carlos I de Borbón, the legitimate heir of the historic dynasty. Succession to the throne shall follow the regular order of primogeniture and representation, the first line having preference over subsequent lines; and within the same line the closer grade over the more remote; and within the same grade the male over female, and in the same sex, the elder over the younger.
Matrilineal primogeniture 
"Matrilineal primogeniture" is a form of succession in which the eldest female child inherits the throne, to the total exclusion of males. The order of succession to the position of the Rain Queen is an example in an African culture of matrilineal primogeniture: not only is dynastic descent reckoned through the female line, but only females are eligible to inherit.
Uterine primogeniture 
A male may also inherit a right of succession through a female ancestor or spouse, to the exclusion of any female relative who might be older or of nearer proximity of blood (see above for Spain's mid-twentieth century dynastic succession law). In such cases, inheritance depends on uterine kinship, so a king would typically be succeeded by his sister's son. This particular system of inheritance applied to the thrones of the Picts of Northern Britain and the Etruscans of Italy. Some kingdoms and tribes in Africa follow the same practice. This usage may stem in part from the certainty of the relationship to the previous king and kings: sons and daughters of a sister are, even if they don't have the same father, his relations (mater semper certa est).
In Democracy in America, Alexis de Tocqueville argues that the abolition of the laws of primogeniture and entail in the law of inheritance of private property (as opposed to inheritance of a monarchy) result in the more rapid division of land and thus force landed people to seek wealth outside the family estate in order to maintain their previous standard of living, accelerating the death of the landed aristocracy and also quickening the shift to democracy.
In Christian Europe, the church had a monopoly on the power to sanction marriage. It discouraged polygamy and divorce. Consequently, in Europe, it was extremely difficult to ensure succession solely by direct male line or even by direct offspring. In Islamic, and Oriental cultures, religion either sanctioned polygyny or use of consorts, or had no authority over marriage; monarchs could consequently ensure sufficient numbers of male offspring to confirm the succession. In such cultures, female heads of state were rare or non-existent. In Japan, the system still mandates that the heir to the throne must be a male, there is only one male grandchild of the current emperor.
The earliest account of primogeniture to be widely known in modern times involved Isaac's son Jacob being born second and Isaac's son Esau being born first  and entitled to the "birthright" (bekhorah בְּכוֹרָה), but eventually selling it to Isaac's second son, Jacob, for a small amount of food. Although the veracity of this account has not been established through other sources, its widespread acceptance shows that primogeniture was sufficiently common in the Middle East for the account to seem plausible to the people living there prior to the Roman Empire.
Roman law 
During the Roman Empire, Roman law governed much of Europe, and the laws pertaining to inheritance made no distinction between the oldest or youngest, male or female, if the deceased left no will. Although admission to the two highest "orders" (ordines, the senators and equestrians) potentially brought lifetime privileges that could be handed down to the next generation, the principle of inherited rank in general was weak. Rather, Roman aristocracy was based on competition, and a Roman family could not maintain its position in the ordines merely through hereditary succession or having title to lands. Although the eldest son typically carried his father's name in some form, he was expected to construct his own career based on competence as an administrator or general and on remaining in favor with the emperor and his council at court. Other than meeting requirements for personal wealth, the qualifications for belonging to the senatorial or equestrian orders varied from generation to generation, and in the later Empire, the dignitas ("esteem") that attended on senatorial or equestrian rank was refined further with additional titles, such as vir illustris, that were not inherited.
Most Roman emperors indicated their choice of successor, usually a close family member or adopted heir, but the presumption that the eldest or even a natural son would inherit was not enshrined. The death of an emperor led to a critical period of uncertainty and crisis. In theory, the Senate was entitled to choose the new emperor, but did so mindful of acclamation by the army or the Praetorian Guard. Thus neither an emperor nor his heir had an inherent "right" to rule, and did so through military power and the Senate's symbolic consent.
Reemergence in medieval and modern times 
The law of primogeniture in Europe has its origins in Medieval Europe; which due to the feudal system necessitated that the estates of land-owning feudal lords be kept as large and united as possible to maintain social stability as well as the wealth, power and social standing of their families.
Adam Smith, in his book An Inquiry into the Nature and Causes of the Wealth of Nations, explains the origin of primogeniture in Europe in the following way:
[W]hen land was considered as the means, not of subsistence merely, but of power and protection, it was thought better that it should descend undivided to one. In those disorderly times, every great landlord was a sort of petty prince. His tenants were his subjects. He was their judge, and in some respects their legislator in peace and their leader in war. He made war according to his own discretion, frequently against his neighbours, and sometimes against his sovereign. The security of a landed estate, therefore, the protection which its owner could afford to those who dwelt on it, depended upon its greatness. To divide it was to ruin it, and to expose every part of it to be oppressed and swallowed up by the incursions of its neighbours. The law of primogeniture, therefore, came to take place, not immediately indeed, but in process of time, in the succession of landed estates, for the same reason that it has generally taken place in that of monarchies, though not always at their first institution.
Historical examples 
A case of agnatic primogeniture is exemplified in the French royal milieu, where the Salic law (attributed to the Salian Franks) forbade any inheritance of a crown through the female line. This rule was adopted to solve the dispute over the legitimate successor of Charles IV of France (Edward III of England or Philip VI of France, though the former would have a stronger claim should proximity of blood be considered, which had never been the case in France since 987, instead as well of both agnatic-cognatic primogeniture or male-preference cognatic primogeniture and the resulting heirs). Conflict between the Salic law and the male-preferred system was also the genesis of Carlism in Spain.
The crowns of Hanover and Great Britain, which had been in personal union since 1714, were separated in 1837 upon the death of King William IV: his niece Victoria inherited the British crown under male-preference primogeniture but, because of semi-Salic law, was ineligible to that of Hanover, which passed to William's eldest surviving brother, Ernest I.
In 1890, the divergence of the thrones of Luxembourg and the Netherlands, both ruled by semi-Salic law, was caused by the fact that the Luxembourg line of succession went back more generations than the Dutch one. The Luxembourg succession was ruled by the provisions of the Nassau House Treaty of 1783. Where the succession is concerned, Luxembourg is the successor state to the Principality of (Orange-)Nassau-Dietz. The Dutch succession only went back to King William I (1815–1840). Therefore Luxembourg still had agnatic heirs from another branch of the House of Nassau left to succeed, while in the Netherlands the male line starting with William I was depleted.
Since the Middle Ages, the semi-Salic principle was prevalent for the inheritance of feudal land in the Holy Roman Empire: inheritance was allowed through females when the male line expired. Females themselves did not inherit, but their male issue could. For example, a grandfather without sons was succeeded by his grandson, the son of his daughter, although the daughter still lived. Likewise, an uncle without sons of his own was succeeded by his nephew, a son of his sister, even if the sister still lived.
Common in feudal Europe outside of Germany was land inheritance based on a form of primogeniture: A lord was succeeded by his eldest son but, failing sons, either by daughters or sons of daughters. In most medieval Western European feudal fiefs, females (such as daughters and sisters) were allowed to succeed, brothers failing. But usually the husband of the heiress became the real lord, assuming his wife's title with the suffix jure uxoris.
In more complex medieval cases, the sometimes conflicting principles of proximity of blood and primogeniture competed, and outcomes were at times unpredictable. Proximity meant that an heir closer in degree of kinship to the lord in question was given precedence although that heir was not necessarily the heir by primogeniture.
- The Burgundian succession in 1361 was resolved in favor of king John II, son of a younger daughter, on basis of blood proximity, being a nearer cousin of the dead duke than Charles II of Navarre, grandson of the elder daughter and son of Jeanne, with only one degree of succession by the women instead of two for the last. Above all, since Charles's mother had already been banned in 1328 from the French crown, as an alleged bastard, she logically couldn't neither obtain for the same reason the duchy of Burgundy. Proximity sometimes favored younger lines (directly contrary to the outcome from applying primogeniture), since it was more probable that from a younger line, a member of an earlier generation was still alive compared with the descendants of the elder line.
- In dispute over the Scottish succession, 1290–91, the Bruce family pleaded tanistry and proximity of blood, whereas Balliol argued his claim based on primogeniture. The arbiter, Edward I of England, decided in favor of primogeniture. But later, the Independence Wars reverted the situation in favor of the Bruce, due to political exigency.
- The Earldom of Gloucester (in the beginning of 14th century) went to full sisters of the dead earl, not to his half-sisters, though they were elder, having been born of the father's first marriage, while the earl himself was from second marriage. Full siblings were considered higher in proximity than half-siblings.
However, primogeniture increasingly won legal cases over proximity in later centuries.
Later, when lands were strictly divided among noble families and tended to remain fixed, agnatic primogeniture (practically the same as Salic Law) became usual: succession going to the eldest son of the monarch; if the monarch had no sons, the throne would pass to the nearest male relative in the male line.
Some countries however accepted female rulers early on, so that if the monarch had no sons, the throne would pass to the eldest daughter. For example, in 1632 Queen Christina of Sweden succeeded to the throne after the death of her father, King Gustav II Adolf.
In England, primogeniture was mandatory for inheritance of land. Until the Statute of Wills was passed in 1540, a will could control only the inheritance of personal property. Real estate (land) passed to the eldest male descendant by operation of law. The statute added a provision that a landowner could "devise" land by the use of a new device called a "testament". The rule of primogeniture in England was not changed until the Administration of Estates Act in 1925.
In law, the rule of inheritance whereby land descends to the oldest son. Under the feudal system of medieval Europe, primogeniture generally governed the inheritance of land held in military tenure (see knight). The effect of this rule was to keep the father’s land for the support of the son who rendered the required military service. When feudalism declined and the payment of a tax was substituted for military service, the need for primogeniture disappeared. In England, consequently, there was enacted the Statute of Wills (1540), which permitted the oldest son to be entirely cut off from inheriting, and in the 17th century military tenure was abolished; primogeniture is, nevertheless, still customary in England. In the United States primogeniture never became widely established.
Other methods of succession 
- "Succession strategies in the Pyrenees in the 19th century: The Basque case".
- SOU 1977:5 Kvinnlig tronföljd, p. 16.
- "New Kerala".
- U-turn on royal succession law change, an April 2008 article from The Daily Telegraph
- Watt, Nicholas (2011-10-28). "Royal equality act will end succession of first born male - rather than older sister". The Guardian. Retrieved 2011-10-28.
- Nobility and Grandee Titles, Spanish Ministry of Justice extracted 05/31/09
- According to the Spanish Ministry of Justice, the default of the succession is by absolute cognatic primogeniture, but the title holder may designate his successor or distribute titles amongst his children, with the eldest getting the highest ranking title.
- Murphy, Michael Dean. "A Kinship Glossary: Symbols, Terms, and Concepts". Retrieved 2006-10-05.
- Nordisk familjebok, Tronföljd, 1920; SOU 1977:5 Kvinnlig tronföljd.
- Título II. De la Corona, Wikisource
- The Royal Household of H.M. The King website
- de Tocqueville, Alexis (1835). "3-The Social Condition of the Anglo-Americans". Democracy in America.
- Genesis 25:26
- Genesis 25:25
- Genesis 25:31-34
- HN.psu.edu Smith, Adam, (1776), Penn State Electronic Classics edition, republished 2005, p.312
- Fergus Millar, "Empire and City, Augustus to Julian: Obligations, Excuses and Status," Journal of Roman Studies 73 (1983), pp. 87–88.
- Keith Hopkins, "The Political Economy of the Roman Empire," in The Dynamics of Ancient Empires: State Power from Assyria to Byzantium (Oxford University Press, 2009), p. 188.
- Hopkins, The Political Economy of the Roman Empire, p. 188.
- Millar, "Empire and City," p. 90, calls them "status-appellations."
- Aloys Winterling, Politics and Society in Imperial Rome (John Wiley & Sons, 2009, originally published 1988 in German), p. 16.
- HN.psu.edu Smith, Adam (1776), Penn State Electronic Classics edition, republished 2005, p.312-313