Tanistry

Tanistry was a system of inheritance practised by the Gaelic nobilities of Ireland, the Isle of Man, and parts of modern Scotland. It was distinctive in having an elected heir known as the tanist (Irish: tánaiste; Scottish Gaelic: tànaiste; Manx: tanishtey). This system was used to select the Chiefs of the Name (head of a clan) and the rulers of the various Gaelic kingdoms in Ireland and in Scotland.

When the chief or king died they were immediately succeeded by the tanist, who had typically been elected years earlier. A new election was then held to select the next tanist. This differs from other systems of elective inheritance, in that an heir was elected in advance of a vacancy, not after the vacancy arose. Valid candidates for the election were restricted to male members of the title holder's sept (extended family); the exact eligibility criteria differed between Ireland and Scotland. The electorate was identical to the set of valid candidates i.e. potential heirs would select a tanist from amongst themselves.

This system ensured that the heir was known in advance (avoiding an interregnum), was always an adult and usually of mature age (avoiding a childhood regency), and kept the title within the sept without being dominated by a single family line. It was very rare to elect a son of the current ruler, instead the tanist would typically be from a different branch of the family. This often led to an informal rotation between several powerful branches. Elections could be controversial and encouraged ambition within the sept, but once a tanist had been elected their succession was usually not contested.

Tanistry is older than recorded history in these regions. It was established in Ireland by the 4th century AD, and subsequently transmitted to Scotland where it merged with the Pictish system. Tanistry operated for multiple centuries, well into the Middle Ages. As English- and Scots-speaking peoples gradually conquered the Gaels, they replaced tanistry with primogeniture. However tanistry persisted in Gaelic-speaking families, particularly for local chiefs, until the 17th century. The terminology was reused by the Republic of Ireland in its 1937 constitution, which established a deputy prime minister known as the Tánaiste.