An heir apparent[note 1] is a person who is first in an order of succession and cannot be displaced from inheriting by the birth of another person. An heir presumptive, by contrast, is someone who is first in line to inherit a title but who can be displaced by the birth of a more eligible heir.
Today these terms most commonly describe heirs to hereditary titles (e.g. titles of nobility) or offices, especially when only inheritable by a single person. Most monarchies refer to the heir apparent of their thrones with the descriptive term of crown prince or crown princess, but they may also be accorded with a more specific substantive title:[note 2] such as Prince of Orange in the Netherlands, Duke of Brabant in Belgium, Prince of Asturias in Spain (also granted to heirs presumptive), or Prince of Wales in the United Kingdom; former titles include Dauphin in the Kingdom of France, and Tsesarevich in Imperial Russia.
The term is also used metaphorically to indicate an expected successor to any position of power, e.g. a political or corporate leader.
This article primarily describes the term heir apparent in a hereditary system regulated by laws of primogeniture—it may be less applicable to cases where a monarch has a say in naming the heir (performed either while alive, e.g. crowning the heir as a rex iunior, or through the monarch's will).
In a hereditary system governed by some form of primogeniture, an heir apparent is easily identifiable as the person whose position as first in the line of succession to a title or office is secure, regardless of future births. An heir presumptive, by contrast, can always be "bumped down" in the succession by the birth of somebody more closely related in a legal sense (according to that form of primogeniture) to the current title-holder.
The clearest example occurs in the case of a childless bearer of a hereditary title that can only be inherited by one person. If at any time the title bearer were to produce children, those children would rank ahead of any person who had formerly been heir presumptive.
Many legal systems assume childbirth is always possible regardless of age or health. In such circumstances a person may be, in a practical sense, the heir apparent but still, legally speaking, heir presumptive. Indeed, when Queen Victoria succeeded her uncle King William IV, the wording of the proclamation even gave as a caveat:
...saving the rights of any issue of his late Majesty King William IV, which may be born of his late Majesty's consort.
This provided for the possibility that William's wife, Adelaide of Saxe-Meiningen, was pregnant at the moment of his death, since such a posthumous child, regardless of its sex, would have displaced Victoria from the throne. Adelaide was 44 at the time, so pregnancy was possible even if unlikely.
Daughters (and their lines) may inherit titles that descend according to male-preference primogeniture, but only in default of sons (and their heirs). That is, both female and male offspring have the right to a place somewhere in the order of succession, but when it comes to what that place is, a female will rank behind her brothers regardless of their ages or her age.
Thus, normally, even an only daughter will not be heir apparent, since at any time a brother might be born who, though younger, would assume that position. Hence, she is an heir presumptive. For example, Queen Elizabeth II was heir presumptive during the reign of her father, King George VI, because at any stage up to his death, George could have fathered a legitimate son.
In a system of absolute primogeniture that disregards gender, female heirs apparent occur. As succession to titles, positions, or offices in the past most often favoured males, females considered to be an heir apparent were rare. Absolute primogeniture was not practised by any modern monarchy for succession to their thrones until the late twentieth century, with Sweden being the first to adopt absolute primogeniture in 1980 and other Western European monarchies following suit.
Since the adoption of absolute primogeniture by contemporary Western European monarchies, examples of female heirs apparent include Crown Princess Victoria of Sweden, Princess Catharina-Amalia of the Netherlands, and Princess Elisabeth of Belgium; they are, respectively, the oldest children of Kings Carl XVI Gustaf, Willem-Alexander, and Philippe. Princess Ingrid Alexandra of Norway is heir apparent to her father, who is heir apparent to the Norwegian throne, and Victoria herself has a female heir apparent in her oldest child, Princess Estelle. Victoria was not heir apparent from birth (in 1977), but gained the status in 1980 following a change in the Swedish Act of Succession. Her younger brother Carl Philip (born 1979) was thus heir apparent for a few months (and is a rare example of an heir apparent losing this status without a death occurring).
In 2015, pursuant to the 2011 Perth Agreement, the Commonwealth realms changed the rules of succession to the 16 thrones of Elizabeth II to absolute primogeniture, except for male heirs born before the Perth Agreement. The effects are not likely to be felt for many years; the first two heirs at the time of the agreement (Charles, Prince of Wales, and his son Prince William, Duke of Cambridge) were already eldest born children, and in 2013 William's first-born son Prince George of Cambridge became the next apparent successor.
But even in legal systems that apply male-preference primogeniture, female heirs apparent are by no means impossible: if a male heir apparent dies leaving no sons but at least one daughter, then the eldest daughter would replace her father as heir apparent to whatever throne or title is concerned, but only when it has become clear that the widow of the deceased is not pregnant. Then, as the representative of her father's line she would assume a place ahead of any more distant relatives. Such a situation has not to date occurred with the English or British throne; several times an heir apparent has died, but each example has either been childless or left a son or sons. However, there have been several female heirs apparent to British peerages (e.g. Frances Ward, 6th Baroness Dudley, and Henrietta Wentworth, 6th Baroness Wentworth).
In one special case, however, England and Scotland had a female heir apparent. The Revolution settlement that established William and Mary as joint monarchs in 1689 only gave the power to continue the succession through issue to Mary II, eldest daughter of the previous king, James II. William, by contrast, was to reign for life only, and his (hypothetical) children by a wife other than Mary would be placed in his original place (as Mary's first cousin) in the line of succession – after Mary's younger sister Anne. Thus, although after Mary's death William continued to reign, he had no power to beget direct heirs, and Anne became the heir apparent for the remainder of William's reign. She eventually succeeded him as Queen of England, Scotland and Ireland.
The position of an heir apparent is normally unshakable: it can be assumed they will inherit. Sometimes, however, extraordinary events—such as the death or the deposition of the parent—intervene.
In some jurisdictions, an heir apparent can automatically lose that status by breaching certain constitutional rules. Today, for example: