The Goidelic branch is also known as Q-Celtic, because Proto-Celtic *kʷ was originally retained in this branch (later losing its labialisation and becoming plain [k]), as opposed to Brythonic, where *kʷ became [p]. This sound change is also found in Gaulish, so Brythonic and Gaulish are sometimes collectively known as "P-Celtic". In Celtiberian, *kʷ is also retained, so the term "Q-Celtic" could be applied to it as well, although Celtiberian is not a Goidelic language.
Early Modern Irish was used as a literary language in Ireland until the 17th century, and its equivalent, Classical Gaelic was used as a literary language in Scotland until the 18th century. Later orthographic divergence is the result of more recent orthographic reforms resulting in standardised pluricentric diasystems. Manx orthography is based on English and Welsh and was introduced in 1610, and was never widely used.
Goidelic is one of the two major divisions of modern-day Insular Celtic languages. The other is the Brythonic languages, which are spoken in Wales, Cornwall and Brittany.
Furthermore, due to the politics of language and national identity, some Irish speakers are offended by the use of the word Gaelic by itself to refer to Irish.
Similarly, Scottish Gaelic speakers find offensive the use of the obsolete word Erse (from Erisch, "Irish") to refer to their language. This term was used in Scotland since at least the late 15th century to refer to Gaelic, which had previously been called Scottis.
The names used in languages themselves (Gaeilge in Irish, Gaelg in Manx, and Gàidhlig in Scottish Gaelic) are derived from Old Irish Goídeleg, which in itself is from the originally more-or-less derogatory term Guoidel meaning "pirate, raider" in Old Welsh. The Goidels called themselves various names according to their tribal/clan affiliations, but the most general seems to have been the name rendered in Latin as Scoti.
The oldest written Goidelic language is Primitive Irish, which is attested in Ogham inscriptions up to about the 4th century AD. Old Irish is found in the margins of Latin religious manuscripts from the 6th century to the 10th century. Middle Irish, the ancestor of the modern Goidelic languages, is the name for the language as used from the 10th to the 12th century: a great deal of literature survives in it, including the early Irish law texts. Early Modern Irish covers the period from the 13th to the 17th century: a form of it was used as a literary language in Ireland and Scotland, consistently until the 17th century and in some cases well into the 18th century. This is often called Classical Irish while the Ethnologue gives the name "Hiberno-Scottish Gaelic" to this purely written language. As long as this written language was the norm, Ireland was considered the Gaelic homeland to the Scottish literati.
The Irish language has been officially recognised as a working language by the European Union. Ireland's national language is the twenty-first to be given such recognition by the EU and previously had the status of a treaty language.
Its historical range was much larger. For example, it was the everyday language of most of the rest of the Highlands until little more than a century ago. Galloway was once also a Gaelic-speaking region, but the Galwegian dialect has been extinct there for approximately two centuries. It is believed to have been home to dialects that were transitional between Scottish Gaelic and the two other Goidelic languages. Most other areas of the Lowlands also spoke forms of Gaelic, the only exceptions being the area which lies on the south-eastern part of the modern border with England - the area called Lothian in the Middle Ages - and the far north-east (parts of Caithness), Orkney and Shetland.
The very word Scotland in fact takes its name from the Latin word for a Gael (Irish), Scotus. So Scotland originally meant Land of the Scots (Irish), or Land of the Gaels. Moreover, until late in the 15th century, it was solely the Gaelic language used in Scotland which in English was called Scottish or - more authentically - Scottis. Scottis continued to be the English name for the language, although it was gradually superseded by the word Erse, an act of cultural disassociation which contributed to the language's declining status. In the early 16th century the dialects of northern Middle English, also known as Early Scots, which had developed in Lothian and had come to be spoken elsewhere in the Kingdom of Scotland themselves later appropriated the name Scots. By the seventeenth century Gaelic speakers were restricted largely to the Highlands and the Hebrides. Furthermore, the culturally repressive measures taken against the rebellious highland communities by the British crown following the 2nd Jacobite Rebellion of 1746 caused still further decline in the language's use - to a large extent by enforced emigration. Even more decline followed in the 19th and early 20th centuries
The Scottish Parliament has afforded the language a secure statutory status and equal respect (but not full equality in legal status within Scots Law
) with English, sparking hopes that Scottish Gaelic can be saved from extinction and perhaps even revived.
Today Manx is used as the sole medium for teaching at five of the island's pre-schools by a company named Mooinjer Veggey, which also operates the sole Manx primary school—the Bunscoill Ghaelgagh. Manx is taught as a second language at all of the Island's primary and secondary schools and also at the Isle of Man College and Centre for Manx Studies.
Shelta language is sometimes thought to be a Goidelic language, but it is, in fact, a cant based on Irish and English, with a primarily English-based syntax.
The Bungee language in Canada is an English dialect spoken by Métis that was influenced by Orkney English, Scots English, Cree, Ojibwe, and Scottish Gaelic.
Pictish was the ancient language of much of modern day Scotland, but its exact relation to the other Celtic languages is not certain.
For extinct Celtic languages of the European mainland, see Continental Celtic languages.