Derbfine

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The derbfine was an Irish agnatic kinship group defined in the law tracts of the eighth century. Its principle purpose was as an institution of property inheritance, with property redistributed on the death of a member to those remaining members of the derbfine. Comprising all the patrilineal descendants over a four-generation group of a common great-grandfather, it gradually gave way to a smaller three-generation kinship group, called the gelfine.

Professor F.J. Byrne of UCD identifies an indfine system used in Ireland before 1000AD which went back to a common great-great-great-grandfather, necessary at a time of frequent warfare.

The inheritance of the Norman royal line on the death of King Stephen and his succession by his cousin Henry I is an example of the derbfine system outside Ireland. Stephen's son was disinherited by consent and Henry was chosen as tánaiste or deputy chief.

The system of male-line descent in an identity-group with a common great-grandfather is still found in countries like Iraq where it is known as the Khamsa system.