The king or chief held office for life and was required by custom to be of full age, in possession of all his faculties, and without any remarkable blemish of mind or body. At the same time, and subject to the same conditions, a tanist or next heir to the monarchy was elected, who if the king died or became disqualified, at once became king. Typically a former king's son became tanist, sometimes the son of the king simultaneously elected but more often a son of a rival branch of the dynasty. Election was based on the principle that the dignity of chieftainship descend to the eldest and most worthy agnate of the last ruler; this differs from the system of
primogeniture. Tanistry still disqualified many in the clan, as most clansmen were clients, not related to the ruling line, patrilineally or otherwise. with the
Red Hand. One of the most common rules for qualification as a
roydammna was that a candidate had to be a member of the previous chief's "
derbfhine", a kindred including all descended in the male line from a common great-grandfather. However, it was often restricted to the chief's
gelfhine, a
fine descended from one common (patrilineal) grandfather. This meant that the group became highly exclusive, keeping the kingship within the dynasty. Many in the wider clan might be reduced to gentry or peasant status (though they might share the surname). These features make tanistry an
agnatic succession mode, and a succession by appointment, as it was an
elective monarchy. Tanistry evades the basic requirement of the
hereditary monarchy, i.e. that the outcome of the succession is predictable, up to the identity of successor and next heirs, by
genealogy. The downside of the large group of eligibles was that increases in
roydammna in each generation might lead to internecine dynastic civil war. Such was the case among the descendants of King and High King
Tairrdelbach Ua Conchobair (1088–1156). His dynasty, the
Uí Briúin, had successfully ruled as
Kings of Connacht since at least the mid-5th century. Their increasing consolidation via the annexation of the Kingdoms of
Mide and
Dublin, plus suborning neighboring states and lordships to vassalage, led to Tairrdelbach becoming the first of his dynasty to become High King. Competition between Tairrdelbach's many sons caused corrosive warfare among at least four competing main lines, in addition to allied lordships' and kingdoms' striving for the main chance. Coupled with the incursions of the
Normans from 1169 onwards, this fragmented Ó Conchobhar rule. By the mid-13th century, they were reduced to ruling a fraction of their former patrimony. Another example of
Derbfhine or
Roydammna proliferation comes from the
Annals of Connacht. It states that at the
Second Battle of Athenry in August 1316, in addition to King Tadc Ó Cellaig of
Uí Maine, "there fell with him ... twenty-eight men who were entitled to succeed to the kingship of Uí Maine." ==Consequences==