Early Irish literature is the oldest vernacular literature in Western Europe. The earliest existing examples of the written Irish language are Ogham inscriptions dating from the 4th century. Extant manuscripts do not go back farther than the 8th century. Two works written by Saint Patrick, his Confessio and Letter to Coroticus were written in Latin some time in the 5th century, and preserved in the Book of Armagh.
The earliest Irish authors
It is unclear when literacy first came to Ireland. The earliest Irish writings are inscriptions, mostly simple memorials, on stone in the ogham alphabet, the earliest of which date to the 4th century. The Latin alphabet was in use by 431, when the fifth century Gaulish chronicler Prosper of Aquitaine records that Palladius was sent by Pope Celestine I as the first bishop to the Irish believers in Christ.Pelagius, an influential British heretic who taught in Rome in the early 5th century, fragments of whose writings survive, is said by Jerome to have been of Irish descent.Coelius Sedulius, the 5th century author of the Carmen Paschale, who has been called the "Virgil of theological poetry", was probably also Irish: the 9th-century Irish geographer Dicuil calls him noster Sedulius ("our Sedulius"), and the Latin name Sedulius usually translates the Irish name Siadal.
Irish literature comprises writings in the Irish, Latin, and English (including Ulster Scots) languages on the island of Ireland. The earliest recorded Irish writing dates from the seventh century and was produced by monks writing in both Latin and Early Irish. In addition to scriptural writing, the monks of Ireland recorded both poetry and mythological tales. There is a large surviving body of Irish mythological writing, including tales such as The Táin and Mad King Sweeny.
The English language was introduced to Ireland in the thirteenth century, following the Norman Conquest of Ireland. The Irish language, however, remained the dominant language of Irish literature down to the nineteenth century, despite a slow decline which began in the seventeenth century with the expansion of English power. The latter part of the nineteenth century saw a rapid replacement of Irish by English in the greater part of the country. At the end of the century, however, cultural nationalism displayed a new energy, marked by the Gaelic Revival (which encouraged a modern literature in Irish) and more generally by the Irish Literary Revival.
Old Irish (Old Irish: Goídelc) (sometimes called Old Gaelic) is the name given to the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from c. AD 600–900. The primary contemporary texts are dated c. AD 700–850; by AD 900 the language had already transitioned into early Middle Irish. Some Old Irish texts date from the 10th century, although these are presumably copies of texts composed at an earlier time period. Old Irish is thus the ancestor of Modern Irish, Manx, and Scottish Gaelic.
Old Irish is known for having a particularly complex system of morphology and especially of allomorphy (more or less unpredictable variations in stems and suffixes in differing circumstances) as well as a complex sound system involving grammatically significant consonant mutations to the initial consonant of a word. Initial consonant mutation must have been present in at least late Common Celtic (Proto-Celtic) because this distinguishing feature has survived with grammatical significance in both modern Welsh and Breton, and the extinct Cornish language also featured. Because the languages belong to the Brittonic branch of the Celtic language group (so-called "P-Celtic"), initial mutation must predate the split in the development paths of the Brittonic and Goidelic languages. No mutations are, however, attested in Gaulish material so a parallel evolution of the phenomenon in the neo-Celtic languages is also possible. Much of the complex allomorphy has been lost, but the rich sound system has been maintained, with little change, in the modern languages.