From The Brehon Laws by Laurence Ginnell, 1894
LAITH may be pronounced Flah. The Flaiths corresponded in some respects to modern nobles, and like them originated in an official aristocracy. Theoretically they were public officers of their respective clans, each being at once the ruler and representative of a sept, were elected on the same principle as the kings, required similar qualifications according to rank, and were provided proportionately with free lands to enable them to support the dignity and perform the duties of the office. They also, like the kings, were allowed to hold at the same time all other property which they might have had or might subsequently inherit or otherwise acquire; and their position gave them some facilities of requisition which other men did not possess. Their official land was in law indivisible; an apparent restriction which in practice became decidedly advantageous to them as a class, as we shall see.
The law gave the right of succession to the most worthy member of the fine of the actual flaith, subject to the right of the clan to determine by election what member of the fine was in fact the most worthy. Hence the flaith's successor might not be his son, though he had sons, but might be a brother, nephew, cousin, or other member of the fine; and while the flaith's private property was on his death divisible among the members of his fine like that of any other individual, his official property with all the permanent structures thereon descended undivided to his successor, in addition to any share of the private property which might fall to that same person as a member of the fine. In course of time the hereditary principle encroached upon and choked the elective, the latter fell into desuetude, and the number of flaiths ceased to correspond to the number of septs. From the office and the land attached to it having been held successively by several succeeding generations of the same family, the flaith gradually learned to regard the land as his own private property, and the people gradually acquiesced; and I find it laid down by a modern writer as the distinguishing mark of a flaith, that he paid no rent, and that a man who paid no rent was a flaith though he owned but a single acre.
This writer completely lost sight of the fact that the flaith was properly an official, and the land he held official land, and not his private property at all. The system under which he lived, and of which he formed a part, laid upon him certain duties for which the lands and revenues assigned him were a provision and a reward, and it was only through the decay and collapse of that system that he could venture to call those lands and revenues his own. The nature of his duties can most conveniently be explained when discussing the next succeeding class of society towards whom most of them were due and owing; and there also it will become very obvious that there was no such inadequate provision made for a flaith as a single acre would have been. It will suffice to mention here that a very high private-property qualification should have been possessed by the family for three successive generations before one could become a flaith at all; and then the official property was given in addition to that. In fact, the flaiths were rather too well provided for, and were so favourably circumstanced that ultimately they almost supplanted the clan as owners of everything.
As the sea attracts all waters, as power and wealth attract to themselves more power and more wealth, the flaith class tended to become great at the expense of the people beneath them. They were constantly taking liberties with, and extending their claims over, land to which they had no just title; and the law under which official property descended contributed to the same result. The idea of private property in land was developing and gathering strength, and land was generally becoming settled under it. The title of every holder, once temporary, was hardening into ownership, and the old ownership of the clan was vanishing, becoming in ordinary cases little more than a superior jurisdiction the exercise of which was rarely invoked. During the time of transition I think the flaith class encroached upon the rights not alone of those below them but of those above them also; that it was chiefly their greed, pride, and disloyalty which led to the breakup of the Irish Monarchy; and that it was for many centuries in their power to restore that monarchy, and with it an independent nationality, had they been sufficiently patriotic.
The flaiths, by virtue of their office, had legal jurisdiction in all matters coming under Urradhus law, or law locally modified. There were various grades or ranks among the flaiths as among modern nobles, but determined by the number of clansmen who paid them tribute; and the territorial limits of a flaith's jurisdiction was wide or narrow as his rank was high or low. When the legal system was in proper working order, plaints involving Cain law, that is, the law contained in the Senchus Mor and administered by the brehons, were required to be lodged at the residence of the Aire-ard before being submitted to the brehons.
A great many varieties of aires are mentioned in the laws; but generally the aire (pronounced arra) appears to have been considered as the type of the full citizen in possession of full legal rights. It was a term not strictly applied, rather a measure of status which different classes might attain than the designation of any particular class. The flaiths and those approaching that rank were aires; and I think every head of a fine was in status an aire though not so called. The aire most frequently spoken of and the aire-desa were recent accessions to the flaith class from the céile class, belonging by birth and descent to the latter, but possessing sufficient property qualification for the former; and, so far as there was progress, may be considered as in a state of transition. The aire-desa was the lowest of the flaith class. Part of his qualification was to have ten free clansmen paying tribute to him. The numbers paying tribute to the different grades of flaiths ranged from ten up to forty, the flaith's rank, honour-price, &c, ranging proportionately. The bo-aire was a man whose wealth consisted mainly in cattle. He was not a flaith.