Crown prince (皇太子)
Kotaishi' (Crown Prince) is the Japanese word used to refer to the prince that is next in line to the imperial throne in Japan. The Japanese word used to refer to the prince that is next in line to a royal throne in other countries, however, is "Otaishi" or just "Taishi". Imperial Highness' is used as his title of honor. He receives the same courteous reception as the present emperor.
Before the Edo period
Crown prince is represented as 東宮 (Togu), 春宮 (Hitsuginomiko) or 太子 (Taishi).
In the Imperial Court, the crown prince who succeeds the throne or who is entitled to succeed it is called 'Oenomiko'. Oenomiko and Crown Prince do not necessarily have the same meaning. Even if he is called Oenomiko, his position is not guaranteed absolutely, and there may be several princes called Oenomiko.
Crown prince does not always refer to the first son of the present emperor. Historically, the Imperial Throne was determined by considering choyo no jo (a uniform order between senior and junior) and capabilities of children and influences of maternal relatives, and the first son could not always become crown prince. Before the order of succession to the Imperial Throne was stipulated, the crown prince meant the son of the current emperor, who was formally installed as Crown Prince.
In the period of the Northern and Southern Courts (Japan) to the mid Edo period, the next heir to the Imperial Throne often did not become 'crown prince' even if he was determined. This was because the ceremonial investiture of the Crown Prince could not be carried out due to economic difficulties of the imperial family. Normally, when the next heir to the Imperial Throne is determined, the ceremonial investiture of the Crown Prince is carried out at the same time or immediately after a few days and the heir becomes Crown Prince. However, if the ceremonial investiture of the Crown Prince was not performed, he was called 'chokun' (crown prince) instead of 'kotaishi' (crown prince). (There were cases in which the ceremonial investiture of the Crown Prince was not performed, like Emperor Koko, Emperor Goshirakawa, and Emperor Gohorikawa, before the Northern and Southern Dynasties, because they were enthroned suddenly.
It is considered that the ceremonial investiture of the Crown Prince was carried out after a manner to the end of the Southern Court (Japan). On the contrary, chokun succeeded to the Imperial Throne without carrying out the ceremonial investiture of the Crown Prince for more than 300 years in the Northern Court (Japan), from Emperor Goenyu to Emperor Reigen who was enthroned after the unification of Southern and Northern Courts.
If a younger brother of the current emperor is the next heir to the Imperial Throne, he is called kotaitei (the younger brother of an Emperor who is heir apparent), and if he is a grandson of the current emperor, he is called kotaison (grandson of an Emperor who is heir apparent). There was only one case in which a woman became a crown princess; Empress Koken succeeded to the Imperial Throne after having been the crown princess in the Nara period.
After the Meiji period
In 1889, the Imperial House Law (Former Imperial House Law) was established as a household law in the imperial court and the order of succession to the Imperial Throne was specified clearly. Article 15 of the Former Imperial House Law specified that a prince who was an heir was crown prince. The first part of article 8 of the current Imperial House Law that was established in 1947 specified that a prince who was the heir was the crown prince. Both 'Imperial Heir' and 'Crown Prince' refer to a legitimate son of the imperial family.
The change of the order of succession to the Imperial Throne is permitted only if 'The Crown Prince has any mental or physical incurable diseases or serious hindrance' (Article 9 of Former Imperial House Act) or 'has any mental or physical incurable diseases or serious hindrance' (Article 3 of Imperial House Law).
Thus, unlike before the establishment of the Imperial House Law, the ceremony of investiture of the Crown Prince is not a requirement of the position of the crown prince. The ceremony of investiture of the Crown Prince is carried out to declare his position to the public in the same way as the Sokui no rei (ceremony of the enthronement). The ceremonial investiture of the infant Crown Prince was carried out before the Edo period. On the contrary, after the establishment of the Imperial House Law, the ceremonial investiture of a Crown Prince is carried out after the crown prince becomes an adult. The crown prince and son of the crown prince become adults at the age of 18 (Article 13 of Former Imperial House Law, Article 22 of current Imperial House Law).
The ceremonial investiture of the Crown Prince was carried out twice after the establishment of the current Imperial House Law.
The ceremonial investiture of the Crown Prince Akihito (November 10, 1952)
The ceremonial investiture of the Crown Prince of Imperial Prince Naruhito (February 23, 1991)
The adult crown prince is first in line to become a Sessho (regent). If the emperor has 'mental or physical diseases or hindrance', but they are temporary and Sessho (regent) is not required, a temporary agent for emperor's constitutional functions is assigned (law concerning agency for emperor's constitutional functions). The order of becoming the agent for emperor's constitutional functions is the same as that of Sessho (regent).
The crown prince (later Emperor Showa) became Sessho from 1921 to 1926. Only crown princes became Sessho after the Restoration of Imperial Rule in Japan. There was a case in which Imperial Prince Naruhito, the first grandson of the Emperor Showa, became an agent when Emperor Showa was treated medically and Crown Prince Akihito was traveling abroad.
The titles of honor of crown prince and crown princess are Imperial Highness like other Imperial Princes and their empresses and Imperial Princesses and princesses (Clause 2 of Article 23 of the current Imperial House Law). Kotaishi (crown prince) is described as 'Kotai Shino' in Kotofu (the genealogy of the Imperial Family).
Kotaitei (the younger brother of an Emperor who is heir apparent), Kotaisei (the nephew of an Emperor who is heir apparent, Kotaison (grandson of an Emperor who is heir apparent)
The current Imperial House Law does not mention kotaitei or kotaisei. The current Imperial House Law mentions kotaison as the 'grandson of the Emperor, who is the Imperial Heir' (the latter part of Article 8 of Imperial House Act).
Crown princes in European countries
The Japanese word 'Kotaishi' corresponds to Crown Prince in English and Kronprinz in German. This was actually used as a title in Germany and other countries.
Today this word is mainly used as a title of crown prince in Scandinavian countries. The current Norwegian crown prince Haakon (Norwegian crown prince) is called H.K.H. Kronprins Haakon, which is translated to HRH Crown Prince Haakon in English.
The crown prince of the Holy Roman Empire was given a title of 'Rex Romanorum' after the heredity of the crown by the Hapsburg was established. The emperors of the Hapsburg gave the title of 'Rex Romanorum' as the next emperor to his successor to maintain heredity of the crown. Napoleon BONAPARTE of the First French Empire appointed his son Napoleon II as 'Rex Romanorum'.
Ceremonial titles are given to apparent heirs as nobles in the Netherlands, Spain, and other countries. The title 'Prins van Oranje' of the crown prince of the Netherlands is derived from a fact that the head of the royal family, Oranje-Nassau family, was a feudal lord of Orange (Oranje in Dutch), Prins van Oranje, in southern France before the foundation of the Netherlands. The crown prince of Spain has a title of 'Principe de Asturias'.
The crown prince in the Kingdom of France was given a title of 'dauphin'. It was originally a title of a feudal lord in the Dauphine region at the south-eastern part of France, but it became a title of crown prince after the region was absorbed as a crown prince region in 1349.
In the Russian Empire, the word 'царевич, tsarevich' that means 'son of czar' was used instead of the aristocratic title in the above countries.
Crown princes in England
The primogeniture with priority to male child is used for succession of the crown in England, and the first son of the king becomes an apparent heir unless there are any reasons for disqualification. The first son of the king is given a title of Prince of Wales, the Duke of Cornwall, or the Duke of Rothesay.
There is no title of Crown Prince in England, and the Duke of Cornwall is often equated to Crown Prince.
Crown princes in Asian countries
Since the Korean peninsula was under the tributary system from the Goryeo period which was subjected to the interference by the Mongolian Empire to Joseon Dynasty, the successor to the king was called '王世子 (crown prince)', but since the Treaty of Shimonoseki was concluded as a result of Sino-Japanese War, Korea was released from the tributary system of the Qing,, the name of the country was changed to Korea and 'Crown Prince' came into use.
However, Korea became a colony of Japan by the annexation of Korea, the former emperor family became a "king" family, and his successor became 王世子 (crown prince) (act of making the former Emperor of Korea a king, defining the titles of crown prince, future successors, and their empresses, and treating them with courteous reception).