The early literature has survived in Middle and Late Middle Irish manuscripts that are, for the most part, miscellaneous collections of prose and verse in which legend, history, bardic and lyric poetry, and medical, legal, and religious writings of several periods are all preserved side by side. The chief works are the Book of the Dun Cow (before 1106), the Book of Leinster (before 1160), and the Yellow Book of Lecan, the Great Book of Lecan, the Lebor Brecc, and the Book of Lismore (late 14th or early 15th cent.). The first three are especially important because they contain the heroic sagas. The oldest writings are poems from the 6th cent.; Dallán Forgaill is the most famous of the filid or official poets. There are also some fine anonymous nature poems from the 8th cent.
With the 9th-century (Middle Irish) period begin the heroic tales in which epic and romance go hand in hand. These stories were classified by the medieval Irish according to type. In modern times they have been divided into two major cycles, the Ulster and the Fenian.
The Ulster cycle deals with swaggering pagan heroes of the century before Christ. Its central hero and the hero of its longest story, Táin Bó Cúalnge [the cattle raid of Cooley], is Cuchulain, an Irish Achilles. The finest of all the Ulster stories is Longes Mac Nusnig [exile of the sons of Usnech], the tragedy of Deirdre. This early Celtic literature is characterized by a simplicity and terseness of style interspersed with richness of imagery, color, and detail.
The Fenian tradition, which became prominent in the late Middle Irish period, is 300 years later than the Ulster. Paganism is modified and Christianity is represented as coming in the extreme old age of Ossian, the poet of the Fenians. The temper is more romantic than epic—the lyrics sing more of nature, love, and separation than of war and death. The characteristic form of this cycle is the ballad. Its ideal hero is Finn, the Irish counterpart of the Welsh Arthur. The Fenian cycle begins with the composition of the long Acallam na Senórech [colloquy of the old men], c.1200. The great prose story of the cycle is Tóraigheacht Agus Ghráinne [the pursuit of Diarmuid and Grainne], a variant of the Ulster story of Deirdre.
Except for Deirdre, the Ulster tales have been forgotten while Fenian legends have survived to modern times, especially in Scotland. The variety of motifs encompassed by the cycles—the doomed lovers, the knights-errant, adventures in an earthly paradise, visions and voyages—influenced medieval romance. The privileged position held by the poet in ancient Ireland was continued after the advent of Christianity. Poets, who were the successors of pagan priests, became guardians of the native tradition, and, after the coming of the Norman English in the 12th and 13th cent., the spokesmen of Gaelic culture. The late medieval prose includes one of the most celebrated Gaelic narrative collections, The Three Sorrows of Storytelling.
The 16th and 17th cent. saw a great poetic revival and the rise of modern Irish prose. Gaelic Ireland was now fighting a losing battle with England, and as the English conquered, Gaelic literature became more passionately patriotic and more militantly Catholic. Prose of the 16th and 17th cent. in Ireland is transitional; it begins with some delightful tales in Middle Irish and comes to its fruition with Geoffrey Keating, whose religious works and monumental historical study of Ireland are the foundation of modern Irish literature. The greatest Irish scholar of the time was Michael O'Clery; among other students of Gaelic culture were some English-speaking Protestants, notably Bedell, bishop of Kilmore and Ardagh, translator of the Old Testament.
The penal age of Ireland may be dated from Cromwell's arrival (1649). During this time Gaelic literature served to keep alive the old culture of the submerged Catholics. From Paris and Louvain came a stream of religious books in Gaelic, probably published by the Franciscans, who at this time became the chief guardians of the Irish language. Even before Cromwell and the intense hardships suffered under English rule, however, bardic poetry had begun to decline. The early 17th cent. was an age of transition from the strict verse of the bardic schools to the less formal meters of untrained poets. Chief among the poets were Aodhagán Ó Raithille, Eóghan Ruadh Ó Súilleabháin, Brian Merriman, and Anthony Raftery.
That period was hardly over before Irish Gaelic received another great blow, following the potato famine of 1847. With the terrible depopulation of Ireland, Gaelic literature began to fade, and the proportion of Gaelic speakers in Ireland dropped in three years from more than three-fourths to one-quarter. Later in the 19th cent., Irish scholarship came into its own again and resulted, through the efforts of John O'Donovan, Eugene O'Curry, Douglas Hyde, and Standish Hayes O'Grady, in a Gaelic literary revival. The principal figures in this new Gaelic literature were Canon Peter O'Leary, Patrick O'Connor, Patrick Henry Pearse, and Maurice O'Sullivan.
The connections between Gaelic Scotland and Gaelic Ireland were close until the rise of Presbyterianism in Scotland. Since the 16th cent., Scots Gaelic has had a literature of its own. The great event of modern Scots Gaelic culture is "the '45," when Bonnie Prince Charlie (Charles Edward Stuart) led the Jacobites in an ultimately unsuccessful uprising. There was a great burst of poetry that defied the repressive measures of Parliament and mourned the English triumph. The poet par excellence of the rebellion was Alexander Macdonald (MacMaster Alasdair); he was more original than Duncan Ban McIntyre, whose poems recall older forms and older themes. At the end of the century came James Macpherson's famous forgery Ossian, supposedly the work of a 3d-century Irish bard.
A sharp decline in technique and content was evident in the 19th cent. Some excellent writers of prose, however, were Dr. Norman Macleod and Donald Mackechnie. In the 20th cent. the best-known poets are Somalirle Maclean, George Campbell Hay, and Derick Thomson. A popular satirist and newspaper columnist was Flann O'Brien (Myles Na Gopaleen), whose novels, particularly At Swim Two Birds (tr. 1956), were popular in translation. In general Scottish Gaels have preserved their language and literary activity better abroad (for instance, in Nova Scotia) than the Irish, but at home Scots Gaelic is disappearing faster than Irish. Most of the monuments of Gaelic literature have been translated into English, as by Lady Gregory, Eleanor Hull, Tom Peete Cross, and (for Scotland) James MacGregor.
See A. Carmichael, ed., Carmina Gadelica (6 vol., 1928-71); D. Thomson, An Introduction to Gaelic Poetry (1974); M. MacLean, The Literature of the Highlands (1988); N. MacNeil, The Literature of the Highlanders (1988).
Another work of a similar nature is Saltair na Rann, written in the tenth centuary.