The Celtic or Keltic languages (usually pronounced /ˈkɛltɪk/ but sometimes /ˈsɛltɪk/) are descended from Proto-Celtic, or "Common Celtic"; a branch of the greater Indo-European language family. The term "Celtic" was first used to describe this language group by Edward Lhuyd in 1707.
Celtic languages are most commonly spoken on the north-western edge of Europe, notably in Ireland, Scotland, Wales, Brittany, Cornwall, and the Isle of Man, and can be found spoken on Cape Breton Island. There are also a substantial number of Welsh speakers in the Patagonia area of Argentina. Some people speak Celtic languages in the other Celtic diaspora areas of the United States, Canada, Australia, and New Zealand. In all these areas, the Celtic languages are now only spoken by minorities though there are continuing efforts at revitalization.
During the 1st millennium BC, they were spoken across Europe, in the Iberian Peninsula, from the Atlantic and North Sea coastlines, up the Rhine valley and down the Danube valley to the Black Sea, the Upper Balkan Peninsula, and in Galatia in Asia Minor. The spread to Cape Breton and Patagonia occurred in modern times. Celtic languages were spoken in Australia before federation in 1901.
SIL Ethnologue lists six "living" Celtic languages, of which four have retained a substantial number of native speakers. These are Irish (Gaeilge) and Scottish Gaelic (descended from Old Irish), Welsh, and Breton, descended from the British language.
The other two, Cornish and Manx, were spoken into modern times but later died as spoken community languages. For both these languages, however, revitalization movements have led to the adoption of these languages by adults and children and produced some native speakers.
Taken together, there were roughly one million native speakers of Celtic languages as of the 2000s. In 2010, there were more than 1.4 million speakers of Celtic languages.
||Number of people who can speak the language
||Main area where the language is spoken
||Around 315,000 consider themselves fluent in the language
||Around 770,700 (2004)
— Wales: 611,000 speakers, around 21.7% of the population of Wales (all skills)
— England: 150,000 
— Chubut Province, Argentina: 5,000 
— United States: 2,500 
— Canada: 2,200 
|Welsh Language Commissioner
In the Republic, 94,000 people use Irish daily outside the education system.
Republic of Ireland:
||Foras na Gaeilge
||Ofis ar Brezhoneg
||58,552 as of 2001  as well as an estimated 400–1000 native speakers on Cape Breton Island
||Bòrd na Gàidhlig
||Keskowethyans an Taves Kernewek
||100, including a small number of children who are new native speakers
||Isle of Man
||Coonceil ny Gaelgey
Classification of Indo-European languages. (click to enlarge)
Proto-Celtic divided into four sub-families:
- Gaulish and its close relatives Galatian, Lepontic, and Noric. Lepontic, the oldest attested Celtic language (from the 6th century BC), is treated as a primary branch by some researchers, including Schumacher, perhaps even the first language to diverge from Proto-Celtic. These languages were once spoken in a wide arc from France to Turkey and from Belgium to northern Italy. They are now all extinct.
- Hispano-Celtic; also extinct:
- Celtiberian, anciently spoken in the Iberian peninsula, in parts of modern Aragón, Old Castile, and New Castile in Spain.
- Gallaecian, anciently spoken in north-western Iberia (north-west Spain and northern Portugal).
- Possibly Lusitanian, from central interior Portugal and western Spain; while its precise classification is unclear, the Indo-European affinity of Lusitanian is not in doubt.
- Possibly Tartessian, written in a script dated to c. 825 BC, from south-western Iberia (southern Portugal and south-west Spain). The mainstream view, however, treats Tartessian as unclassified, with no obvious external relationship.
- Brythonic, including the living languages Breton, Cornish, and Welsh, and the extinct languages Cumbric and Pictish though possibly Pictish may be a sister language rather than a daughter of British (Common Brythonic). Before the arrival of Scotti on the Isle of Man in the 9th century, there may have been a Brythonic language in the Isle of Man.
- Goidelic, including the living languages Irish, Manx, and Scottish Gaelic.
Scholarly handling of the Celtic languages has been rather argumentative owing to lack of much primary source data. Some scholars (such as Cowgill 1975; McCone 1991, 1992; and Schrijver 1995) distinguish Continental Celtic and Insular Celtic, arguing that the differences between the Goidelic and Brythonic languages arose after these split off from the Continental Celtic languages. Other scholars (such as Schmidt 1988) distinguish between P-Celtic and Q-Celtic, putting most of the Gaulish and Brythonic languages in the former group and the Goidelic and Celtiberian languages in the latter. The P-Celtic languages (also called Gallo-Brittonic) are sometimes seen (for example by Koch 1992) as a central innovating area as opposed to the more conservative peripheral Q-Celtic languages.
The Breton language is Brythonic, not Gaulish, though there may be some input from the latter. When the Anglo-Saxons moved into Great Britain, several waves of the native Britons crossed the English Channel and landed in Brittany. They brought with them their Brythonic language, which evolved into Breton – still partially intelligible by modern Welsh and Cornish speakers.
In the P/Q classification schema, the first language to split off from Proto-Celtic was Gaelic. It has characteristics that some scholars see as archaic, but others see as also being in the Brythonic languages (see Schmidt). In the Insular/Continental classification schema, the split of the former into Gaelic and Brythonic is seen as being late.
The distinction of Celtic into these four sub-families most likely occurred about 900 BC according to Gray and Atkinson but, because of estimation uncertainty, it could be any time between 1200 and 800 BC. However, they only considered Gaelic and Brythonic. The controversial paper by Forster and Toth included Gaulish and put the break-up much earlier at 3200 BC ± 1500 years. They support the Insular Celtic hypothesis. The early Celts were commonly associated with the archaeological Urnfield culture, the Hallstatt culture, and the La Tène culture, though the earlier assumption of association between language and culture is now considered to be less strong.
There are two main competing schemata of categorization. The older schema, argued for by Schmidt (1988) among others, links Gaulish with Brythonic in a P-Celtic node, originally leaving just Goidelic as Q-Celtic. The difference between P and Q languages is the treatment of Proto-Celtic *kʷ, which became *p in the P-Celtic languages but *k in Goidelic. An example is the Proto-Celtic verb root *kʷrin- "to buy", which became pryn- in Welsh but cren- in Old Irish. However, a classification based on a single feature is seen as risky by its critics, particularly as the sound change occurs in other language groups (especially the Osco-Umbrian and Greek).
The other schema, defended for example by McCone (1996), links Goidelic and Brythonic together as an Insular Celtic branch, while Gaulish and Celtiberian are referred to as Continental Celtic. According to this theory, the "P-Celtic" sound change of [kʷ] to [p] occurred independently or areally. The proponents of the Insular Celtic hypothesis point to other shared innovations among Insular Celtic languages, including inflected prepositions, VSO word order, and the lenition of intervocalic [m] to [β̃], a nasalised voiced bilabial fricative (an extremely rare sound). There is, however, no assumption that the Continental Celtic languages descend from a common "Proto-Continental Celtic" ancestor. Rather, in the Insular/Continental schema, Celtiberian is usually considered to be the first branch to split from Proto-Celtic, and the remaining group would later have split into Gaulish and Insular Celtic.
There are legitimate scholarly arguments in favour of both the Insular Celtic hypothesis and the P-Celtic/Q-Celtic hypothesis. Proponents of each schema dispute the accuracy and usefulness of the other's categories. However, since the 1970s the division into Insular and Continental Celtic has become the more widely held view (Cowgill 1975; McCone 1991, 1992; Schrijver 1995), but in the middle of the 1980s, the P-Celtic/Q-Celtic hypothesis found new supporters (Lambert 1994), because of the inscription on the Larzac piece of lead (1983), the analysis of which reveals another common phonetical innovation -nm- > -nu (Gaelic ainm / Gaulish anuana, Old Welsh enuein "names"), that is less accidental than only one. The discovery of a third common innovation, would allow the specialists to come to the conclusion of a Gallo-Brythonic dialect (Schmidt 1986; Fleuriot 1986).
It must be noted that the interpretation of this and further evidence is still quite contested, and the main argument in favour of Insular Celtic is connected with the development of the verbal morphology and the syntax in Irish and British Celtic, which Schumacher regards as convincing, while he considers the P-Celtic/Q-Celtic division unimportant and treats Gallo-Brittonic as an outdated hypothesis.
When referring only to the modern Celtic languages, since no Continental Celtic language has living descendants, "Q-Celtic" is equivalent to "Goidelic" and "P-Celtic" is equivalent to "Brythonic".
Within the Indo-European family, the Celtic languages have sometimes been placed with the Italic languages in a common Italo-Celtic subfamily, a hypothesis that is now largely discarded, in favour of the assumption of language contact between pre-Celtic and pre-Italic communities.
How the family tree of the Celtic languages is ordered depends on which hypothesis is used:
Characteristics of Celtic languages
Although there are many differences between the individual Celtic languages, they do show many family resemblances. While none of these characteristics are necessarily unique to the Celtic languages, there are few if any other languages which possess them all. They include:
- consonant mutations (Insular Celtic only)
- inflected prepositions (Insular Celtic only)
- two grammatical genders (modern Insular Celtic only; Old Irish and the Continental languages had three genders)
- a vigesimal number system (counting by twenties)
- e.g. Cornish whetek ha dew ugens "fifty-six" (literally "sixteen and two twenty")
- verb–subject–object (VSO) word order (probably Insular Celtic only)
- an interplay between the subjunctive, future, imperfect, and habitual, to the point that some tenses and moods have ousted others
- an impersonal or autonomous verb form serving as a passive or intransitive
- Welsh dysgaf "I teach" vs. dysgir "is taught, one teaches", Irish "déanaim" "I do/make" vs. "déantar" "is done"
- no infinitives, replaced by a quasi-nominal verb form called the verbal noun or verbnoun
- frequent use of vowel mutation as a morphological device, e.g. formation of plurals, verbal stems, etc.
- use of preverbal particles to signal either subordination or illocutionary force of the following clause
- mutation-distinguished subordinators/relativisers
- particles for negation, interrogation, and occasionally for affirmative declarations
- infixed pronouns positioned between particles and verbs
- lack of simple verb for the imperfective "have" process, with possession conveyed by a composite structure, usually BE + preposition
- Cornish yma kath dhymm "I have a cat", literally "there is a cat to me"
- use of periphrastic phrases to express verbal tense, voice, or aspectual distinctions
- distinction by function of the two versions of BE verbs traditionally labelled substantive (or existential) and copula
- bifurcated demonstrative structure
- suffixed pronominal supplements, called confirming or supplementary pronouns
- use of singulars and/or special forms of counted nouns, and use of a singulative suffix to make singular forms from plurals, where older singulars have disappeared
(Irish) Ná bac le mac an bhacaigh is ní bhacfaidh mac an bhacaigh leat.
(Literal translation) Don't bother with son the beggar's and not will-bother son the beggar's with-you.
- bhacaigh is the genitive of bacach. The igh the result of affection; the bh is the lenited form of b.
- leat is the second person singular inflected form of the preposition le.
- The order is verb–subject–object (VSO) in the second half. Compare this to English or French (and possibly Continental Celtic) which are normally subject–verb–object in word order.
(Welsh) pedwar ar bymtheg a phedwar ugain
(literally) four on fifteen and four twenties
- bymtheg is a mutated form of pymtheg, which is pump ("five") plus deg ("ten"). Likewise, phedwar is a mutated form of pedwar.
- The multiples of ten are deg, ugain, deg ar hugain, deugain, hanner cant, trigain, deg a thrigain, pedwar ugain, deg a phedwar ugain, cant.
||estuary, mouth of a river
|tu fas, tu allan
||tobac a chaitheamh
Article 1 of the Universal Declaration of Human Rights:
All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.
- Irish: Saolaítear na daoine uile saor agus comhionann ina ndínit agus ina gcearta. Tá bua an réasúin agus an choinsiasa acu agus dlíd iad féin d'iompar de mheon bráithreachais i leith a chéile.
- Manx: Ta dagh ooilley pheiagh ruggit seyr as corrym ayns ard-cheim as kiartyn. Ren Jee feoiltaghey resoon as cooinsheanse orroo as by chair daue ymmyrkey ry cheilley myr braaraghyn.
- Scottish Gaelic: Tha gach uile dhuine air a bhreth saor agus co-ionnan ann an urram 's ann an còirichean. Tha iad air am breth le reusan is le cogais agus mar sin bu chòir dhaibh a bhith beò nam measg fhein ann an spiorad bràthaireil.
- Breton: Dieub ha par en o dellezegezh hag o gwirioù eo ganet an holl dud. Poell ha skiant zo dezho ha dleout a reont bevañ an eil gant egile en ur spered a genvreudeuriezh.
- Cornish: Pub den oll yw genys frank ha kehaval yn dynita ha gwiryow. Yth yns i enduys gans reson ha cowses hag y tal dhedhans gwul dhe udn orth y gila yn spyrys a vredereth.
- Welsh: Genir pawb yn rhydd ac yn gydradd â'i gilydd mewn urddas a hawliau. Fe'u cynysgaeddir â rheswm a chydwybod, a dylai pawb ymddwyn y naill at y llall mewn ysbryd cymodlon.
- ^ "American Heritage Dictionary. Celtic: kel-tik, sel". Dictionary.reference.com. http://dictionary.reference.com/browse/celtic. Retrieved 2011-08-19.
- ^ Cunliffe, Barry W. 2003. The Celts: a very short introduction. P.48
- ^ "Language by State – Scottish Gaelic" on Modern Language Association website. Retrieved 27 December 2007
- ^ "Languages Spoken At Home" from Australian Government Office of Multicultural Interests website. Retrieved 27 December 2007
- ^ Languages Spoken:Total Responses from Statistics New Zealand website. Retrieved 5 August 2008
- ^ Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. ABC-CLIO. pp. 34, 365–366, 529, 973, 1053. http://books.google.com.au/books?id=f899xH_quaMC&printsec=frontcover&dq=Celtic+Culture:+A+Historical+Encyclopedia#v=onepage&q&f=false. Retrieved 15 June 2010.
- ^ "A brief history of the Cornish language". Maga Kernow. http://www.magakernow.org.uk/index.aspx?articleid=38590#Revival.
- ^ Beresford Ellis, Peter (1990, 1998, 2005). The Story of the Cornish Language. Tor Mark Press. pp. 20–22. ISBN 0-85025-371-3.
- ^ a b Published on Thu 20 15 Mar:54:30 GMT 2008. "Fockle ny ghaa: schoolchildren take charge". Iomtoday.co.im. http://www.iomtoday.co.im/manx-language/Fockle-ny-ghaa-schoolchildren-take.3901786.jp. Retrieved 2011-08-19.
- ^ "'South West:TeachingEnglish:British Council:BBC". BBC/British Council website (BBC). 2010. http://www.teachingenglish.org.uk/uk-languages/south-west. Retrieved 2010-02-09.
- ^ "Celtic Languages". Ethnologue. http://www.ethnologue.com/show_family.asp?subid=1164-16. Retrieved 9 March 2010.
- ^ Crystal, David (2010). The Cambridge Encyclopedia of Language. Cambridge University Press. ISBN 978-0-521-73650-3.
- ^ "2004 Welsh Language Use Survey: the report" (PDF). http://linguistics.uoregon.edu/files/admin/file/Course_Documents/Survey_Methods/Survey%20Reports/Welsh%20Survey%20&%20Report%2004.pdf. Retrieved 5 June 2012.
- ^ United Nations High Commissioner for Refugees. "Refworld | World Directory of Minorities and Indigenous Peoples - United Kingdom : Welsh". UNHCR. http://www.unhcr.org/refworld/topic,463af2212,488f25df2,49749c8cc,0.html. Retrieved 2010-05-23.
- ^ "Wales and Argentina". Wales.com website. Welsh Assembly Government. 2008. http://www.wales.com/en/content/cms/English/International_Links/Wales_and_the_World/Wales_and_Argentina/Wales_and_Argentina.aspx. Retrieved 23 January 2012.
- ^ "Table 1. Detailed Languages Spoken at Home and Ability to Speak English for the Population 5 Years and Over for the United States: 2006-2008 Release Date: April, 2010" (xls). United States Census Bureau. 27 April 2010. http://www.census.gov/hhes/socdemo/language/data/other/detailed-lang-tables.xls. Retrieved 2 January 2011.
- ^ "2006 Census of Canada: Topic based tabulations: Various Languages Spoken (147), Age Groups (17A) and Sex (3) for the Population of Canada, Provinces, Territories, Census Metropolitan Areas and Census Agglomerations, 2006 Census - 20% Sample Data". Statistics Canada. 7 December 2010. http://www12.statcan.gc.ca:80/census-recensement/2006/dp-pd/tbt/Rp-eng.cfm?A=R&APATH=3&D1=0&D2=0&D3=0&D4=0&D5=0&D6=0&DETAIL=0&DIM=0&FL=A&FREE=0&GC=01&GID=837928&GK=1&GRP=1&LANG=E&O=D&PID=89189&PRID=0&PTYPE=88971%2C97154&S=0&SHOWALL=0&SUB=0&TABID=1&THEME=70&Temporal=2006&VID=0&VNAMEE=&VNAMEF=. Retrieved 3 January 2011.
- ^ "| Irish Examiner". Archives.tcm.ie. 2004-11-24. http://archives.tcm.ie/irishexaminer/2004/11/24/story517225942.asp. Retrieved 2011-08-19.
- ^ Christina Bratt Paulston. Linguistic Minorities in Multilingual Settings: Implications for Language Policies. J. Benjamins Pub. Co. p. 81. ISBN 1-55619-347-5.
- ^ Pierce, David (2000). Irish Writing in the Twentieth Century. Cork University Press. p. 1140. ISBN 1-85918-208-9.
- ^ Ó hÉallaithe, Donncha (1999). Cuisle.
- ^ a b Central Statistics Office, 'Census 2011 - This is Ireland - see table 33a'www.cso.ie
- ^ (French) Données clés sur breton, Ofis ar Brezhoneg
- ^ "UNESCO Atlas of the World's Languages in Danger, 2010". Unesco.org. http://www.unesco.org/culture/languages-atlas/en/atlasmap/language-id-411.html. Retrieved 2011-08-19.
- ^ "CHIN/RCIP – Festivities". Virtualmuseum.ca. 1999-04-19. http://www.virtualmuseum.ca/Exhibitions/Festiva1/en/uccb/cont2/index.html. Retrieved 2011-08-19.
- ^ "de beste bron van informatie over highlandclearances. Deze website is te koop!". highlandclearances.info. http://www.highlandclearances.info/clearances/postclearances_influenceabroad_canada.htm. Retrieved 2011-08-19.
- ^ "Mixed report on Gaelic language". BBC News. 2005-10-10. http://news.bbc.co.uk/1/low/scotland/4326424.stm. Retrieved 2011-08-19.
- ^ some 600 children brought up as bilingual native speakers (2003 estimate, SIL Ethnologue).
- ^ s About 2,000 fluent speakers. "'South West:TeachingEnglish:British Council:BBC". BBC/British Council website (BBC). 2010. http://www.teachingenglish.org.uk/uk-languages/south-west. Retrieved 2010-02-09.
- ^ "Anyone here speak Jersey?". Independent.co.uk. 2002-04-11. http://www.independent.co.uk/news/education/education-news/anyone-here-speak-jersey-657175.html. Retrieved 2011-08-19.
- ^ "Documentation for ISO 639 identifier: glv". Sil.org. 2008-01-14. http://www.sil.org/iso639-3/documentation.asp?id=glv. Retrieved 2011-08-19.
- ^ "2006 Official Census, Isle of Man". Gov.im. 2006-04-23. http://www.gov.im/treasury/economic/census/2006/. Retrieved 2011-08-19.
- ^ "Shelta". Ethnologue. http://www.ethnologue.com/show_language.asp?code=sth. Retrieved 9 March 2010.
- ^ "ROMLEX: Romani dialects". Romani.uni-graz.at. http://romani.uni-graz.at/romlex/dialects.xml. Retrieved 2011-08-19.
- ^ a b Schumacher, Stefan; Schulze-Thulin, Britta; aan de Wiel, Caroline (2004) (in German). Die keltischen Primärverben. Ein vergleichendes, etymologisches und morphologisches Lexikon. Innsbruck: Institut für Sprachen und Kulturen der Universität Innsbruck. pp. 84–87. ISBN 3-85124-692-6.
- ^ Cólera, Carlos Jordán (16 March 2007). "The Celts in the Iberian Peninsula:Celtiberian". e-Keltoi 6: 749–750. http://www4.uwm.edu/celtic/ekeltoi/volumes/vol6/6_17/jordan_6_17.pdf. Retrieved 16 June 2010.
- ^ Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. ABC-CLIO. p. 481. http://books.google.com.au/books?id=f899xH_quaMC&printsec=frontcover&dq=Celtic+Culture:+A+Historical+Encyclopedia#v=snippet&q=hispano-celtic&f=false.
- ^ "Ethnographic Map of Pre-Roman Iberia (circa 200 B.C.)". Arkeotavira.com. http://www.arkeotavira.com/Mapas/Iberia/Populi.htm. Retrieved 2011-08-19.
- ^ Prósper, B. M. (2002). Lenguas y religiones prerromanas del occidente de la península ibérica. Ediciones Universidad de Salamanca. pp. 422–427. ISBN 84-7800-818-7.
- ^ Villar F., B. M. Prósper. (2005). Vascos, Celtas e Indoeuropeos: genes y lenguas. Ediciones Universidad de Salamanca. pp. 333–350. ISBN 84-7800-530-7.
- ^ a b c Koch, John T (2010). Celtic from the West Chapter 9: Paradigm Shift? Interpreting Tartessian as Celtic. Oxbow Books, Oxford, UK. pp. 187–295. ISBN 978-1-84217-410-4.
- ^ a b c Koch, John T (2011). Tartessian 2: The Inscription of Mesas do Castelinho ro and the Verbal Complex. Preliminaries to Historical Phonology. Oxbow Books, Oxford, UK. pp. 1–198. ISBN 978-1-907029-07-3. http://www.oxbowbooks.com/bookinfo.cfm/ID/91450//Location/Oxbow.
- ^ Broderick, George (2010). "Die vorrömischen Sprachen auf der iberischen Halbinsel". In Hinrichs, Uwe (in German). Das Handbuch der Eurolinguistik (1st ed.). Wiesbaden, Germany: Otto Harrassowitz Verlag. pp. 304–305. ISBN 3-447-05928-1. http://books.google.com.au/books?id=3VDH7oKtViYC&pg=PA305&lpg=PA305&dq=LOGORO+Tartessische+Inschriften+Die+vorr%C3%B6mischen+Sprachen+auf+der+iberischen#v=onepage&q&f=false.
- ^ Kenneth H. Jackson suggested that there were two Pictish languages, a pre-Indo-European one and a Pritenic Celtic one. This has been challenged by some scholars. See Katherine Forsyth's "Language in Pictland: the case against 'non-Indo-European Pictish'" EtextPDF (27.8 MB). See also the introduction by James & Taylor to the "Index of Celtic and Other Elements in W. J. Watson's 'The History of the Celtic Place-names of Scotland'" EtextPDF (172 KB). Compare also the treatment of Pictish in Price's The Languages of Britain (1984) with his Languages in Britain & Ireland (2000).
- ^ Kenneth Jackson used the term "Brittonic" for the form of the British language after the changes in the 6th century.
- ^ Barbour and Carmichael, Stephen and Cathie (2000). Language and nationalism in Europe. Oxford University Press. p. 56. ISBN 978-0-19-823671-9. http://books.google.com/?id=1ixmu8Iga7gC&pg=PA56&lpg=PA56&dq=Breton+Gaulish+words&q=Breton%20Gaulish%20words.
- ^ Gray and Atkinson, RD; Atkinson, QD (2003). "Language-tree divergence times support the Anatolian theory of Indo-European origin". Nature 426 (6965): 435–439. Bibcode 2003Natur.426..435G. DOI:10.1038/nature02029. PMID 14647380.
- ^ Rexova, K.; Frynta, D and Zrzavy, J. (2003). "Cladistic analysis of languages: Indo-European classification based on lexicostatistical data". Cladistics 19 (2): 120–127. DOI:10.1111/j.1096-0031.2003.tb00299.x.
- ^ Forster, Peter; Toth, Alfred (2003). Toward a phylogenetic chronology of ancient Gaulish, Celtic, and Indo-European. The National Academy of Sciences.
- Ball, Martin J. & James Fife (ed.) (1993). The Celtic Languages. London: Routledge. ISBN 0-415-01035-7.
- Borsley, Robert D. & Ian Roberts (ed.) (1996). The Syntax of the Celtic Languages: A Comparative Perspective. Cambridge: Cambridge University Press. ISBN 0521481600.
- Cowgill, Warren (1975). "The origins of the Insular Celtic conjunct and absolute verbal endings". In H. Rix. Flexion und Wortbildung: Akten der V. Fachtagung der Indogermanischen Gesellschaft, Regensburg, 9.–14. September 1973. Wiesbaden: Reichert. pp. 40–70. ISBN 3-920153-40-5.
- Celtic Linguistics, 1700–1850 (2000). London; New York: Routledge. 8 vols comprising 15 texts originally published between 1706 and 1844.
- Forster, Peter; Toth, Alfred (July 2003). "Toward a phylogenetic chronology of ancient Gaulish, Celtic, and Indo-European". Proc. Natl. Acad. Sci. U.S.A. 100 (15): 9079–84. DOI:10.1073/pnas.1331158100. PMC 166441. PMID 12837934. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=12837934.
- Gray, Russell D.; Atkinson, Quintin D. (November 2003). "Language-tree divergence times support the Anatolian theory of Indo-European origin". Nature 426 (6965): 435–9. Bibcode 2003Natur.426..435G. DOI:10.1038/nature02029. PMID 14647380.
- Hindley, Reg (1990). The Death of the Irish Language: A Qualified Obituary. Routledge. ISBN 0-415-04339-5.
- Lewis, Henry & Holger Pedersen (1989). A Concise Comparative Celtic Grammar. Göttingen: Vandenhoeck & Ruprecht. ISBN 3-525-26102-0.
- McCone, Kim (1991). "The PIE stops and syllabic nasals in Celtic". Studia Celtica Japonica 4: 37–69.
- McCone, Kim (1992). "Relative Chronologie: Keltisch". In R. Beekes, A. Lubotsky, and J. Weitenberg (eds.). Rekonstruktion und relative Chronologie: Akten Der VIII. Fachtagung Der Indogermanischen Gesellschaft, Leiden, 31. August–4. September 1987. Institut für Sprachwissenschaft der Universität Innsbruck. pp. 12–39. ISBN 3-85124-613-6.
- McCone, K. (1996). Towards a Relative Chronology of Ancient and Medieval Celtic Sound Change. Maynooth: Department of Old and Middle Irish, St. Patrick's College. ISBN 0-901519-40-5.
- Russell, Paul (1995). An Introduction to the Celtic Languages. Longman. ISBN 0-582-10082-8.
- Schmidt, K. H. (1988). "On the reconstruction of Proto-Celtic". In G. W. MacLennan. Proceedings of the First North American Congress of Celtic Studies, Ottawa 1986. Ottawa: Chair of Celtic Studies. pp. 231–48. ISBN 0-09-693260-0.
- Schrijver, Peter (1995). Studies in British Celtic historical phonology. Amsterdam: Rodopi. ISBN 90-5183-820-4.
- Schumacher, Stefan; Schulze-Thulin, Britta; aan de Wiel, Caroline (2004) (in German). Die keltischen Primärverben. Ein vergleichendes, etymologisches und morphologisches Lexikon. Innsbruck: Institut für Sprachen und Kulturen der Universität Innsbruck. ISBN 3-85124-692-6.