Why might a society use the same kinship term for a father and a father’s brother?

In anthropology, a society may use the same kinship term for a father and his brother as part of a classificatory system. In these systems, certain collateral kin—relatives outside of one's direct line of descent—are grouped with lineal kin.1

This practice is often found in societies with unilineal descent, where the kinship terminology emphasizes the social importance of a specific lineage. By using the same term, the society highlights the shared membership of these individuals within the same generational cohort and lineage, rather than focusing solely on biological distinction. Specifically, this is a feature of bifurcate merging terminology, where collateral relatives are identified with lineal relatives when the connecting relative is of the same sex.12

It is important to note that using a single term does not mean individuals are socially indistinguishable; members of such societies are typically well aware of who their biological father is. Instead, these terms convey broader social information about roles, responsibilities, and lineage within the community.1