The Irish geis, pl. geasa, which may be rendered by Tabu, had two senses. It meant something which must not be done for fear of disastrous consequences, and also an obligation to do something commanded by another.
As a tabu the geis had a large place in Irish life, and was probably known to other branches of the Celts.881 It followed the general course of tabu wherever found. Sometimes it was imposed before birth, or it was hereditary, or connected with totemism. Legends, however, often arose giving a different explanation to geasa, long after the customs in which they originated had been forgotten. It was one of Diarmaid's geasa not to hunt the boar of Ben Gulban, and this was probably totemic in origin. But legend told how his father killed a child, the corpse being changed into a boar by the child's father, who said its span of life would be the same as Diarmaid's, and that he would be slain by it. Oengus put geasa on Diarmaid not to hunt it, but at Fionn's desire he broke these, and was killed.882 Other geasa—those of Cúchulainn not to eat dog's flesh, and of Conaire never to chase birds—also point to totemism.
In some cases geasa were based on ideas of right and wrong, honour or dishonour, or were intended to cause avoidance of unlucky days. Others are unintelligible to us. The largest number of geasa concerned kings and chiefs, and are described, along with their corresponding privileges, in the Book of Rights. Some of the geasa of the king of Connaught were not to go to an assembly of women at Leaghair, not to sit in autumn on the sepulchral mound of the wife of Maine, not to go in a grey-speckled garment on a grey-speckled horse to the heath of Cruachan, and the like.883 The meaning of these is obscure, but other examples are more obvious and show that all alike corresponded to the tabus applying to kings in primitive societies, who are often magicians, priests, or even divine representatives. On them the welfare of the tribe and the making of rain or sunshine, and the processes of growth depend. They must therefore be careful of their actions, and hence they are hedged about with tabus which, however unmeaning, have a direct connection with their powers. Out of such conceptions the Irish kingly geasa arose. Their observance made the earth fruitful, produced abundance and prosperity, and kept both the king and his land from misfortune. In later times these were supposed to be dependent on the "goodness" or the reverse of the king, but this was a departure from the older idea, which is clearly stated in the Book of Rights.884 The kings were divinities on whom depended fruitfulness and plenty, and who must therefore submit to obey their geasa. Some of their prerogatives seem also to be connected with this state of things. Thus they might eat of certain foods or go to certain places on particular days.885 In primitive societies kings and priests often prohibit ordinary mortals from eating things which they desire for themselves by making them tabu, and in other cases the fruits of the earth can only be eaten after king or priest has partaken of them ceremonially. This may have been the case in Ireland. The privilege relating to places may have meant that these were sacred and only to be entered by the king at certain times and in his sacred capacity.
As a reflection from this state of things, the heroes of the sagas, Cúchulainn and Fionn, had numerous geasa applicable to themselves, some of them religious, some magical, others based on primitive ideas of honour, others perhaps the invention of the narrators.886
Geasa, whether in the sense of tabus or of obligations, could be imposed by any one, and must be obeyed, for disobedience produced disastrous effects. Probably the obligation was framed as an incantation or spell, and the power of the spell being fully believed in, obedience would follow as a matter of course.887 Examples of such geasa are numerous in Irish literature. Cúchulainn's father-in-law put geasa on him that he should know no rest until he found out the cause of the exile of the sons of Doel. And Grainne put geasa on Diarmaid that he should elope with her, and this he did, though the act was repugnant to him.
Among savages the punishment which is supposed to follow tabu-breaking is often produced through auto-suggestion when a tabu has been unconsciously infringed and this has afterwards been discovered. Fear produces the result which is feared. The result is believed, however, to be the working of divine vengeance. In the case of Irish geasa, destruction and death usually followed their infringement, as in the case of Diarmaid and Cúchulainn. But the best instance is found in the tale of The Destruction of Da Derga's Hostel, in which the síd-folk avenge themselves for Eochaid's action by causing the destruction of his descendant Conaire, who is forced to break his geasa. These are first minutely detailed; then it is shown how, almost in spite of himself, Conaire was led on to break them, and how, in the sequel, his tragic death occurred.888 Viewed in this light as the working of divine vengeance to a remote descendant of the offender by forcing him to break his tabus, the story is one of the most terrible in the whole range of Irish literature.
The religious interdictions mentioned by Cæsar (vi. 13) may be regarded as tabus, while the spoils of war placed in a consecrated place (vi. 18), and certain animals among the Britons (v. 12), were clearly under tabu.
Joyce, OCR 332 f.
Book of Rights, ed. O'Donovan, 5.
Book of Rights, 7.
Ibid. 3 f.
LL 107; O'Grady, ii. 175.
In Highland tales geasa is translated "spells."
RC xxii. 27 f. The story of Da Choca's Hostel has for its subject the destruction of Cormac through breaking his geasa (RC xxi. 149 f.).