Gaelic Societies based on kinship were known as early as the 20th century. In spite of the reality of their existence, an official definition of a clan did not appear until the Acts of the Scottish Parliament in 1587 and 1593. In the 1587 Act there was a roll of "The Names of the Landislords and Baillis of the Lands in the Hielands and Ilis". A second roll was compiled in 1594. Even though an official definition was not available, some clans were acknowledged at an earlier date; such as the Inneses who were first recognized as a clan by the King's Privy Council in 1597.
The Acts defined a clan as consisting of either persons linked by blood or persons linked by reason of place of dwelling in a territory. A blood relationship included cadet branches recognized under the Law of Arms. A relationship based on place of dwelling included the vassals, tenants and occupiers of land under a territorial chief along with "ancient adherents" who had followed the chief for over three generations. This definition of a clan led to the situation where clan adherents could bear a different name from the clan and yet be recognized as a Sept of a clan.
In addition to Septs arising from the definition in the 1587/1593 Acts, there can be numerous spelling variants. Some were acquired locally (in Scotland), but many came into being when people emigrated to other countries. Often new arrivals could not write, and had little or no documentation. Names were recorded by immigration officials as they heard them spoken, frequently with a strong accent.