Selecting a chief- Patrilineal Descent.
Firstly, the office and title is passed patrilineally (from father to child) in descending order of male birth then descending order of female birth, hence the oldest surviving son is the classed as the heir presumptive.
If the heir presumptive produces no heirs, then on the heir presumptive’s death the office and title goes to the next younger son, etc., then eldest daughter, etc.
The term cadet is used to describe family groups which are descendants of younger sons, thus the oldest surviving son of each generation maintains the main or principal family line and younger sons establish cadet lines.
In the case of the chiefly line of Carruthers the first recognised house was Carruthers of Mouswald and the last was Carruthers of Holmains from which sprung the cadet line of Dormont and those cadets can have their own cadet lines.
When a chiefly line is extinguished in the case of a Mouswald, the most recent cadet line to branch off the chiefly line eg Holmains, becomes the new chiefly line. In the case of Carruthers, Holmains continues through the female line of Susan Carruthers, 3rd daughter of John, 12th of Holmains.
Maintenance of Surname
Secondly the office and title is implicitly linked to the surname, thus an Elliott, a Maxwell or a Douglas etc. cannot be chief of Clan Carruthers . In some cases, where the heir is a daughter, arrangements have been made so that her husband and children assume her surname, and thus the office and title can be passed to her offspring.
This practice has given rise to the use of compound (hyphenated or ‘double-barrelled’) names as in the case of one branch, the Mitchell-Carruthers while the other has reverted back to Carruthers. The matter of principal names was established by the Lord Lyon Innes of Learney when in the case of Monro-Lucas-Tooth that he was a Tooth rather than a Monro or Lucas.
It is now clearly established that it is the last name which decides the matter. Thus by the Court of the Lord Lyon (the heraldry court of Scotland), a Moodie-Buchanan is consider a Buchanan but a Buchanan-Moodie is considered a Moodie. Further, in the case of a chief as the representer of the family, the surname cannot be a compound name.