The deposeddisinheritance of a crown prince (廃太子)
The deposed/disinheritance of a crown prince means to disinherit a heir in an imperial family or royal family. This refers to the disinheritance of a heir to the throne, such as a crown prince or dauphin, or such person who was deposed of the title. The term is only used for disinheritance of a prince who has been investitured as a crown prince.
Although many of the disinheritance cases resulted from imperial-court or political strives, as in the example of Sun He, who was a prince of Wu who lived in the Three Kingdoms period (China), heirs were often disinherited because they were deemed incompetent as a crown prince on an emergent basis. The examples of incompetence include a political stance different from the emperor or king, who is his father, or characteristic or behavioral abnormalities such as violence or incontinence, which lead to disinheritance in general described earlier. Health problems or weak constitution could also be a reason for disinheritance. Even when a prince himself is decent and healthy, he could still be disinherited if he did not have a heir, especially a son, or due to the troubles arising from his marriage and their consequences. In the Former Han dynasty of ancient China, there was a prince who could not receive investiture of the crown prince or ascend the throne due to the troubles at his wife's parents' home, despite his distinguished service in defeating maternal relatives (Lu shi).
Because a prince is the successor of an emperor or king, who is the leader of a country, and gives a great impact on his environment, he is judged by severer standards than those applied to heirs of other important families or aristocrats, and a minor misconduct which may be acceptable for aristocrats in general could often lead to disinheritance. On the other hand, if a prince is disinherited carelessly, the selection of his successor could raise havoc in the imperial court and its environment, or even cause a civil war or disruption of the country in the worst-case scenario. For this reason, disinheritance is often reserved as the final trump card. Because disinheritance is the last resort, whether or not to disinherit a prince is a very difficult decision. In the example of Sun He earlier mentioned, the conflict between the Sun He faction and the Sun Ba (who was Sun He's younger brother) faction was caused by the Emperor Sun Quan, who was their father who favored Sun Ba.
When the conflict lead to a national disruption, the old Sun Quan used the last resort and disinherited Sun He (conflict of two princes. Sun Ba was also punished, and the third prince became the crown prince.)
The deposed/disinheritance of crown prince in Japan
There were some cases of the deposed/disinheritance of a crown prince in Japan. Most of them resulted from the political strives involving the Fujiwara clan or the conflicts in the imperial court. In some cases, the crown prince voluntarily chose to relinquish the title of the crown prince, as in the case of the Imperial Prince Atsuakira. There are additional cases in the period of the Northern and Southern Courts (Japan), including the Imperial Prince Naohito, who was deposed as a result of the military defeat rather than by political reasons.
The cases of deposed/disinheritance of a crown prince in Japan are quite different from those in other countries in that they do not necessarily mean the end of the political life of the prince. As in the example of the Imperial Prince Tsunesada, who lived in the Heian period, there are some cases in which a once deposed prince was requested to ascend the throne.
For information, the current Imperial House Law of Japan prohibits a crown prince's secession from the Imperial Family, or his declining the right of succession to the Imperial Throne. This is to prevent a 'voluntary' secession resulting from a conspiracy or plot. In addition, it is stipulated that if an imperial heir has a fatal mental or physical illness, or met a fatal accident, the Imperial Household Council can alter the succession order to the throne. In the old system, the former Imperial House Law article 52 defined the disciplinary punishment for the Imperial Family members including the deposition of privileges, and it was legally viable to disinherit a crown prince.