The word clan is derived from the Gaelic word clanna, meaning children. However, the need for proved descent from a common ancestor related to the chiefly house is too restrictive. Clans developed a territory based on the native men who came to accept the authority of the dominant group in the vicinity. A clan also included a large group of loosely related septs – dependent families – all of whom looked to the clan chief as their head and their protector.
A romantic depiction of Highland Chiefs from 1831
According to the former Lord Lyon, Sir Thomas Innes of Learney,  a clan is a community that is distinguished by heraldry and recognised by the Sovereign. Learney considered clans to be a "noble incorporation" because the arms borne by a clan chief are granted or otherwise recognised by the Lord Lyon as an officer of the Crown, thus conferring royal recognition to the entire clan. Clans with recognised chiefs are therefore considered a noble community under Scots law. A group without a chief recognised by the Sovereign, through the Lord Lyon, has no official standing under Scottish law. Claimants to the title of chief are expected to be recognised by the Lord Lyon as the rightful heir to the undifferenced arms of the ancestor of the clan of which the claimant seeks to be recognized as chief. A chief of a clan is the only person who is entitled to bear the undifferenced arms of the ancestral founder of the clan. The clan is considered to be the chief's heritable estate and the chief's Seal of Arms is the seal of the clan as a "noble corporation". Under Scots law, the chief is recognised as the head of the clan and serves as the lawful representative of the clan community.
Historically, a clan was made up of everyone who lived on the chief's territory, or on territory of those who owed allegiance to the said chief. Through time, with the constant changes of "clan boundaries", migration or regime changes, clans would be made up of large numbers of members who were unrelated and who bore different surnames. Often, those living on a chief's lands would, over time, adopt the clan surname. A chief could add to his clan by adopting other families, and also had the legal right to outlaw anyone from his clan, including members of his own family. Today, anyone who has the chief's surname is automatically considered to be a member of the chief's clan. Also, anyone who offers allegiance to a chief becomes a member of the chief's clan, unless the chief decides not to accept that person's allegiance.
Clan membership goes through the surname. Children who take their father's surname are part of their father's clan and not their mother's. However, there have been several cases where a descendant through the maternal line has changed their surname in order to claim the chiefship of a clan, such as the late chief of the Clan MacLeod who was born John Wolridge-Gordon and changed his name to the maiden name of his maternal grandmother in order to claim the chiefship of the MacLeods. Today, clans may have lists of septs. Septs are surnames, families or clans that historically, currently or for whatever reason the chief chooses, are associated with that clan. There is no official list of clan septs, and the decision of what septs a clan has is left up to the clan itself. Confusingly, sept names can be shared by more than one clan, and it may be up to the individual to use his or her family history or genealogy to find the correct clan they are associated with.
Several clan societies have been granted coats of arms. In such cases, these arms are differenced from the chief's, much like a clan armiger. The former Lord Lyon King of Arms, Thomas Innes of Learney stated that such societies, according to the Law of Arms, are considered an "indeterminate cadet".
Authority of the clans (the dùthchas and the oighreachd)
Scottish clanship contained two complementary but distinct concepts of heritage. These were firstly the collective heritage of the clan, known as their dùthchas, which was their prescriptive right to settle in the territories in which the chiefs and leading gentry of the clan customarily provided protection. This concept was where all clansmen recognised the personal authority of the chiefs and leading gentry as trustees for their clan. The second concept was the wider acceptance of the granting of charters by the Crown and other powerful land owners to the chiefs, chieftains and lairds which defined the estate settled by their clan. This was known as their oighreachd and gave a different emphasis to the clan chief's authority in that it gave the authority to the chiefs and leading gentry as landed proprietors, who owned the land in their own right, rather than just as trustees for the clan. From the beginning of Scottish clanship, the clan warrior elite, who were known as the ‘fine’, strove to be landowners as well as territorial war lords.
Clans, the law and the legal process
The concept of dùthchas mentioned above held precedence in the Middle Ages; however, by the early modern period the concept of oighreachd was favoured. This shift reflected the importance of Scots law in shaping the structure of clanship in that the fine were awarded charters and the continuity of heritable succession was secured. The heir to the chief was known as the tainistear and was usually the direct male heir. However, in some cases the direct heir was set aside for a more politically accomplished or belligerent relative. There were not many disputes over succession after the 16th century and, by the 17th century, the setting aside of the male heir was a rarity. This was governed and restricted by the law of Entail, which prevented estates from being divided up amongst female heirs and therefore also prevented the loss of clan territories.
The main legal process used within the clans to settle criminal and civil disputes was known as arbitration, in which the offending and aggrieved sides put their cases to a panel that was drawn from the leading gentry and was overseen by the clan chief. There was no appeal against the decision made by the panel, which was usually recorded in the local Royal or Burgh court.
Fosterage and Manrent were the most important forms of social bonding in the clans. In the case of fosterage, the chief's children would be brought up by a favored member of the leading clan gentry and in turn their children would be favored by members of the clan.
In the case of manrent, this was a bond contracted by the heads of families looking to the chief for territorial protection, though not living on the estates of the clan elite. These bonds were reinforced by calps, death duties paid to the chief as a mark of personal allegiance by the family when their head died, usually in the form of their best cow or horse. Although calps were banned by Parliament in 1617, manrent continued covertly to pay for protection.
The marriage alliance reinforced links with neighboring clans as well as with families within the territory of the clan. The marriage alliance was also a commercial contract involving the exchange of livestock, money and land through payments in which the bride was known as the tocher and the groom was known as the dowry.
Rents from those living within the clan estate were collected by the tacksmen. These lesser gentry acted as estate managers, allocating the runrig strips of land, lending seed-corn and tools and arranging the droving of cattle to the Lowlands for sale, taking a minor share of the payments made to the clan nobility, the fine. They had the important military role of mobilizing the Clan Host, both when required for warfare and more commonly as a large turnout of followers for weddings and funerals, and traditionally, in August, for hunts which included sports for the followers, the predecessors of the modern Highland games.
Clan disputes and disorder
Where the oighreachd (land owned by the clan elite or fine) did not match the common heritage of the dùthchas (the collective territory of the clan) this led to territorial disputes and warfare. The fine resented their clansmen paying rent to other landlords. Some clans used disputes to expand their territories. Most notably, the Clan Campbell and the Clan Mackenzie were prepared to play off territorial disputes within and among clans to expand their own land and influence. Feuding on the western seaboard was conducted with such intensity that the Clan MacLeod and the Clan MacDonald on the Isle of Skye were reputedly reduced to eating dogs and cats in the 1590s.
Feuding was further compounded by the involvement of Scottish clans in the wars between the Irish Gaels and the English Tudor monarchy in the 16th century. Within these clans, there evolved a military caste of members of the lesser gentry who were purely warriors and not managers, and who migrated seasonally to Ireland to fight as mercenaries.
There was heavy feuding between the clans during the civil wars of the 1640s; however, by this time, the chiefs and leading gentry preferred increasingly to settle local disputes by recourse to the law. After the Restoration of the monarchy in 1660, the incidents of feuding between clans declined considerably. The last "clan" feud that led to a battle and that was not part of a civil war was the Battle of Mulroy, which took place on 4 August 1688.
Cattle raiding, known as "reiving", had been normal practice prior to the 17th century. It was also known as creach, where young men took livestock from neighbouring clans. By the 17th century, this had declined and most reiving was known as sprèidh, where smaller numbers of men raided the adjoining Lowlands and the livestock taken usually being recoverable on payment of tascal (information money) and guarantee of no prosecution. Some clans, such as the Clan MacFarlane and the Clan Farquharson, offered the Lowlanders protection against such raids, on terms not dissimilar to blackmail.