Irish is the most deeply researched among all Gaelic languages. It has very long history, and nowadays linguists know several stages of Irish: Insular Irish, Archaic Irish (circa 400-800), Old Irish (circa 800-1000), Middle Irish (circa 1000-1500), Classical Irish and Modern Colloquial Irish. It is possible to have such a long development, because Ogham inscriptions, found in Ireland, prove it was the earliest of all Goidelic languages. The insciptions date back to the 5th century AD and contain several words even now heard in Irish. Rich literature of Old Irish epoch allowed to study this language thoroughly, Middle Irish also has its numerous sources. After Ireland was unified with England - for good and all in the 17th century - Irish population began to die out fast. Religious rebellions, uprisings for independence - they all caused to severe repressions of Irish people. Population also died of hunger, frequent on the island, or emigrated to America. . In the past century, the number of Irish-speaking persons has declined from 50 percent of the population of Ireland to less than 20 percent. In the 19th century one could be sure Irish Gaelic would soon become extinct
 
But that didn't happen. This century Ireland gained finally its independence, and now the language again comes into power in the Republic. It is taught at schools, it is heard on the radio and television, and in rural areas there are still numerous people who use it every day at home. Now we can breathe freely - Irish is no longer endangered.

Originally a highly inflected language, as it was in Old epoch, Irish retains now essentially two noun cases, nominative and genitive, with the dative surviving in the singular of feminine nouns (though Classical language still uses dative widely); the language has present, past, future simple verb tenses in the indicative mood, also some complex tenses. Celtic initial mutations present everywhere in Irish in two forms: aspiration, or lenition, and nasalisation, or eclipsis. Linguists still argue about the origin of these interesting phenomenon which cannot be met in Continental Celtic languages. Maybe you can try to open this secret and take up Irish? We have some links to Old Irish (why not to start from the beginning period?) resources on the Web and soon we will publish a complete Old Irish grammar in our Indo-European Grammars.
 

Old Irish Links
Modern Irish Links