CLAN (Gaelic clann, O. Ir. cland, connected with Lat. planta, shoot or scion, the ancient Gaelic or Goidelic substituting k for p), a group of people united by common blood, and usually settled in a common habitat. The clan system existed in Ireland and the Highlands of Scotland from early times. In its strictest sense the system was peculiar to those countries, but, in its wider meaning of a group of kinsmen forming a self-governing community, the system as represented by the village community has been shown by Sir H. Maine and others to have existed at one time or another in all lands.
Before the use of surnames and elaborate written genealogies, a tribe in its definite sense was called in Celtic a tuath, a word of wide affinities, from a root tu, to grow, to multiply, existing in all European languages. When the tribal system began to be broken up by conquest and by the rise of towns and of territorial government, the use of a common surname furnished a new bond for keeping up a connexion between kindred. The head of a tribe or smaller group of kindred selected some ancestor and called himself his Ua, grandson, or as it has been anglicized O', e.g. Ua Conchobair (O' Conor), Ua Suilleabhain (O'Sullivan). All his kindred adopted the same name, the chief using no fore-name however. The usual mode of distinguishing a person before the introduction of surnames was to name his father and grandfather, e.g. Owen, son of Donal, son of Dermot. This naturally led some to form their surnames with Mac, son, instead of Ua, grandson, e.g. MacCarthaigh, son of Carthach (MacCarthy), MacRuaidhri, son of Rory (Macrory). Both methods have been followed in Ireland, but in Scotland Mac came to be exclusively used. The adoption of such genealogical surnames fostered the notion that all who bore the same surname were kinsmen, and hence the genealogical term clann, which properly means the descendants of some progenitor, gradually became synonymous with tuath, tribe. Like all purely genealogical terms, clann may be used in the limited sense of a particular tribe governed by a chief, or in that of many tribes claiming descent from a common ancestor. In the latter sense it was synonymous with síl, siol, seed e.g. Siol Alpine, a great clan which included the smaller clans of the Macgregors, Grants, Mackinnons, Macnabs, Macphies, Macquarries and Macaulays.
The clan system in the most archaic form of which we have any definite information can be best studied in the Irish tuath, or tribe.  This consisted of two classes: (1) tribesmen, and (2) a miscellaneous class of slaves, criminals, strangers and their descendants. The first class included tribesmen by blood in the male line, including all illegitimate children acknowledged by their fathers, and tribesmen by adoption or sons of tribeswomen by strangers, foster-sons, men who had done some signal service to the tribe, and lastly the descendants of the second class after a certain number of generations. Each tuath had a chief called a ríg, king, a word cognate with the Gaulish ríg-s or rix, the Latin reg-s or rex, and the Old Norse rik-ir. The tribesmen formed a number of communities, each of which, like the tribe itself, consisted of a head, ceann fine, his kinsmen, slaves and other retainers. This was the fine, or sept. Each of these occupied a certain part of the tribe-land, the arable part being cultivated under a system of co-tillage, the pasture land co-grazed according to certain customs, and the wood, bog and mountains forming the marchland of the sept being the unrestricted common land of the sept. The sept was in fact a village community.
What the sept was to the tribe, the homestead was to the sept. The head of a homestead was an aire, a representative freeman capable of acting as a witness, compurgator and bail. These were very important functions, especially when it is borne in mind that the tribal homestead was the home of many of the kinsfolk of the head of the family as well as of his own children. The descent of property being according to a gavel-kind custom, it constantly happened that when an aire died the share of his property which each member of his immediate family was entitled to receive was not sufficient to qualify him to be an aire. In this case the family did not divide the inheritance, but remained together as "a joint and undivided family," one of the members being elected chief of the family or household, and in this capacity enjoyed the rights and privileges of an aire. Sir H.S. Maine directed attention to this kind of family as an important feature of the early institutions of all Indo-European nations. Beside the "joint and undivided family," there was another kind of family which we might call "the joint family." This was a partnership composed of three or four members of a sept whose individual wealth was not sufficient to qualify each of them to be an aire, but whose joint wealth qualified one of the co-partners as head of the joint family to be one.
So long as there was abundance of land each family grazed its cattle upon the tribe-land without restriction; unequal increase of wealth and growth of population naturally led to its limitation, each head of a homestead being entitled to graze an amount of stock in proportion to his wealth, the size of his homestead, and his acquired position. The arable land was no doubt applotted annually at first; gradually, however, some of the richer families of the tribe succeeded in evading this exchange of allotments and converting part of the common land into an estate in sevralty. Septs were at first colonies of the tribe which settled on the march-land; afterwards the conversion of part of the common land into an estate in sevralty enabled the family that acquired it to become the parent of a new sept. The same process might, however, take place within a sept without dividing it; in other words, several members of the sept might hold part of the land of the sept as separate estate. The possession of land in sevralty introduced an important distinction into the tribal system - it created an aristocracy. An aire whose family held the same land for three generations was called a flaith, or lord, of which rank there were several grades according to their wealth in land and chattels. The aires whose wealth consisted in cattle only were called bó-aires, or cow-aires, of whom there were also several grades, depending on their wealth in stock. When a bó-aire had twice the wealth of the lowest class of flaith he might enclose part of the land adjoining his house as a lawn; this was the first step towards his becoming a flaith. The relations which subsisted between the flaiths and the bó-aires formed the most curious part of the Celtic tribal system, and throw a flood of light on the origin of the feudal system. Every tribesman without exception owed ceilsinne to the ríg, or chief, that is, he was bound to become his ceile, or vassal. This consisted in paying the ríg a tribute in kind, for which the ceile was entitled to receive a proportionate amount of stock without having to give any bond for their return, giving him service, e.g. in building his dun, or stronghold, reaping his harvest, keeping his roads clean and in repair, killing wolves, and especially service in the field, and doing him homage three times while seated every time he made his return of tribute. Paying the "calpe" to the Highland chiefs represented this kind of vassalage, a colpdach or heifer being in many cases the amount of food-rent paid by a free or saer ceile. A tribesman might, however, if he pleased, pay a higher rent on receiving more stock together with certain other chattels for which no rent was chargeable. In this case he entered into a contract, and was therefore a bond or daer ceile. No one need have accepted stock on these terms, nor could he do so without the consent of his sept, and he might free himself at any time from his obligation by returning what he had received, and the rent due thereon.
What every one was bound to do to his ríg, or chief, he might do voluntarily to the flaith of his sept, to any flaith of the tribe, or even to one of another tribe. He might also become a bond ceile. In either case he might renounce his ceileship by returning a greater or lesser amount of stock than what he had received according to the circumstances under which he terminated his vassalage. In cases of disputed succession to the chiefship of a tribe the rival claimants were always anxious to get as many as possible to become their vassals. Hence the anxiety of minor chieftains, in later times in the Highlands of Scotland, to induce the clansmen to pay the "calpe" where there happened to be a doubt as to who was entitled to be chief.
The effect of the custom of gavel-kind was to equalize the wealth of each and leave no one wealthy enough to be chief. The "joint and undivided family" and the formation of "joint families," or gilds, was one way of obviating this result; another way was the custom of tanistry. The headship of the tribe was practically confined to the members of one family; this was also the case with the headship of a sept. Sometimes a son succeeded his father, but the rule was that the eldest and most capable member of the geilfine, that is, the relatives of the actual chief to the fifth degree,  was selected during his lifetime to be his successor - generally the eldest surviving brother or son of the preceding chief. The man selected as successor to a chief of a tribe, or chieftain of a sept, was called the tanist, and should be "the most experienced, the most noble, the most wealthy, the wisest, the most learned, the most truly popular, the most powerful to oppose, the most steadfast to sue for profits and (be sued) for losses." In addition to these qualities he should be free from personal blemishes and deformities and of fit age to lead his tribe or sept, as the case may be, to battle.  So far as selecting the man of the geilfine who was supposed to possess all those qualities, the office of chief of a tribe or chieftain of a sept was elective, but as the geilfine was represented by four persons, together with the chief or chieftain, the election was practically confined to one of the four. In order to support the dignity of the chief or chieftain a certain portion of the tribe or sept land was attached as an apanage to the office; this land, with the duns or fortified residences upon it, went to the successor, but a chief's own property might be gavelled. This custom of tanistry applied at first probably to the selection of the successors of a ríg, but was gradually so extended that even a bó-aire had a tanist.
A sept might have only one flaith, or lord, connected with it, or might have several. It sometimes happened, however, that a sept might be so broken and reduced as not to have even one man qualified to rank as a flaith. The rank of a flaith depended upon the number of his ceiles, that is, upon his wealth. The flaith of a sept, and the highest when there was more than one, was ceann fine, or head of the sept, or as he was usually called in Scotland, the chieftain. He was also called the flaith geilfine, or head of the geilfine, that is, the kinsmen to the fifth degree from among whom should be chosen the tanist, and who, according to the custom of gavel-kind, were the immediate heirs who received the personal property and were answerable for the liabilities of the sept. The flaiths of the different septs were the vassals of the ríg, or chief of the tribe, and performed certain functions which were no doubt at first individual, but in time became the hereditary right of the sept. One of those was the office of maer, or steward of the chief's rents, etc.;  and another that of aire tuisi, leading aire, or taoisech, a word cognate with the Latin duc-s or dux, and Anglo-Saxon here-tog, leader of the "here," or army. The taoisech was leader of the tribe in battle; in later times the term seems to have been extended to several offices of rank. The cadet of a Highland clan was always called the taoisech, which has been translated captain; after the conquest of Wales the same term, tywysaug, was used for a ruling prince. Slavery was very common in Ireland and Scotland; in the former slaves constituted a common element in the stipends or gifts which the higher kings gave their vassal sub-reguli. Female slaves, who were employed in the houses of chiefs and flaiths in grinding meal with the hand-mill or quern, and in other domestic work, must have been very common, for the unit or standard for estimating the wealth of a bó-aire, blood-fines, etc., was called a cumhal, the value of which was three cows, but which literally meant a female slave. The descendants of those slaves, prisoners of war, forfeited hostages, refugees from other tribes, broken tribesmen, etc., gathered round the residence of the ríg and flaiths, or squatted upon their march-lands, forming a motley band of retainers which made a considerable element in the population, and one of the chief sources of the wealth of chiefs and flaiths. The other principal source of their income was the food-rent paid by ceiles, and especially by the daer or bond ceiles, who were hence called biathachs, from biad, food. A flaith, but not a ríg, might, if he liked, go to the house of his ceile and consume his food-rent in the house of the latter.
Under the influence of feudal ideas and the growth of the modern views as to ownership of land, the chiefs and other lords of clans claimed in modern times the right of best owing the tribe-land as turcrec, instead of stock, and receiving rent not for cattle and other chattels as in former times, but proportionate to the extent of land given to them. The turcrec-land seems to have been at first given upon the same terms as turcrec-stock, but gradually a system of short leases grew up; sometimes, too, it was given on mortgage. In the Highlands of Scotland ceiles who received turcrec-land were called "taksmen." On the death of the chief or lord, his successor either bestowed the land upon the same person or gave it to some other relative. In this way in each generation new families came into possession of land, and others sank into the mass of mere tribesmen. Sometimes a "taksman" succeeded in acquiring his land in perpetuity, by gift, marriage or purchase, or even by the "strong hand." The universal prevalence of exchangeable allotments, or the rundale system, shows that down to even comparatively modern times some of the land was still recognized as the property of the tribe, and was cultivated in village communities.
The chief governed the clan by the aid of a council called the sabaid (sab, a prop), but the chief exercised much power, especially over the miscellaneous body of non-tribesmen who lived on his own estate. This power seems to have extended to life and death. Several of the flaiths, perhaps, all heads of septs, also possessed somewhat extensive powers of the same kind.
The Celtic dress, at least in the middle ages, consisted of a kind of shirt reaching to a little below the knees called a lenn, a jacket called an inar, and a garment called a brat, consisting of a single piece of cloth. This was apparently the garb of the aires, who appear to have been further distinguished by the number of colours in their dress, for we are told that while a slave had clothes of one colour, a rég tuatha, or chief of a tribe, had five, and an ollamh and a superior king six. The breeches was also known, and cloaks with a cowl or hood, which buttoned up tight in front. The lenn is the modern kilt, and the brat the plaid, so that the dress of the Irish and Welsh in former times was the same as that of the Scottish Highlander.
By the abolition of the heritable jurisdiction of the Highland chiefs, and the general disarmament of the clans by the acts passed in 1747 after the rebellion of 1745, the clan system was practically broken up, though its influence still lingers in the more remote districts. An act was also passed in 1747 forbidding the use of the Highland garb; but the injustice and impolicy of such a law being generally felt it was afterwards repealed.(W. K. S.)
 The following account of the Irish clan-system differs in some respects from that in the article on Brehon Laws (q.v.); but it is retained here in view of the authority of the writer and the admitted obscurity of the whole subject.
(ED. E. B.)
 The explanation here given of geilfine is different from that given in the introduction to the third volume of the Ancient Laws of Ireland, which was followed by Sir H.S. Maine in his account of it in his Early History of Institutions, and which the present writer believes to be erroneous.
 This office is of considerable importance in connexion with early Scottish history. In the Irish annals the ríg, or chief of a great tribe (mor tuath), such as of Ross, Moray, Marr, Buchan, etc., is called a mor maer, or great maer. Sometimes the same person is called king also in these annals. Thus Findlaec, or Finlay, son of Ruadhri, the father of Shakespeare's Macbeth, is called king of Moray in the Annals of Ulster, and mor maer in the Annals of Tighernach. The term is never found in Scottish charters, but it occurs in the Book of the Abbey of Deir in Buchan, now in the library of the university of Cambridge. The Scotic kings and their successors obviously regarded the chiefs of the great tribes in question merely as their maers, while their tribesmen only knew them as kings. From these "mor-maerships," which corresponded with the ancient mor tuatha, came most, if not all, the ancient Scottish earldoms.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)