|Ireland, Scotland, Mann, Wales, Cornwall, Brittany|
Insular Celtic languages are those Celtic languages that originated in the British Isles, in contrast to the Continental Celtic languages of mainland Europe and Anatolia. All surviving Celtic languages are from the Insular Celtic group; the Continental Celtic languages are extinct. The six Insular Celtic languages of modern times can be divided into:
- the Goidelic languages: Irish, Manx, and Scottish Gaelic
- the Brythonic languages: Breton, Cornish, and Welsh (another language or dialect, Cumbric, is extinct.)
Insular Celtic hypothesis 
The "Insular Celtic hypothesis" is a theory that the Brythonic and Goidelic languages evolved together in those islands, having a common ancestor more recent than any shared with the Continental Celtic languages such as Celtiberian, Gaulish, Galatian and Lepontic, among others, all of which are long extinct.
The proponents of the Insular Celtic hypothesis (such as Cowgill 1975; McCone 1991, 1992; and Schrijver 1995) point to shared innovations among Insular Celtic languages, including inflected prepositions, shared use of certain verbal particles, VSO word order, and the differentiation of absolute and conjunct verb endings as found extensively in Old Irish and to a small extent in Middle Welsh (see Morphology of the Proto-Celtic language). They assert that a partition that lumps the Brythonic languages and Gaulish (P-Celtic) on one side and the Goidelic languages with Celtiberian (Q-Celtic) on the other may be a superficial one (i.e. owing to a language contact phenomenon), as the identical sound shift (/kʷ/ to /p/) could have occurred independently in the predecessors of Gaulish and Brythonic, or have spread through language contact between those two groups.
The family tree of the Insular Celtic languages is thus as follows:
- Insular Celtic
The following table lists cognates showing the development of Proto-Celtic */kʷ/ to /p/ in Gaulish and the Brythonic languages but to /k/ in the Goidelic languages.
|Proto-Celtic||Gaulish||Welsh||Cornish||Breton||Primitive Irish||Modern Irish||Scots Gaelic||Manx||English|
|*kʷeis||pis||pwy||piw||piv||*qeis||cé (older cia)||cò/cia||quoi||"who"|
A significant difference between Goidelic and Brythonic languages is the transformation of *an, am to a denasalised vowel with lengthening, é, before an originally voiceless stop or fricative, cf. Old Irish éc "death", écath "fish hook", dét "tooth", cét "hundred" vs. Welsh angau, angad, dant, and cant. Otherwise:
- the nasal is retained before a vowel, i̯, w, m, and a liquid:
- Old Irish ben "woman" (< *benā)
- Old Irish gainethar "he/she is born" (< *gan-i̯e-tor)
- Old Irish ainb "ignorant" (< *anwiss)
- the nasal passes to en before another n:
- Old Irish benn "peak" (< *banno) (vs. Welsh bann)
- Middle Irish ro-geinn "finds a place" (< *ganne) (vs. Welsh gannaf)
- the nasal passes to in, im before a voiced stop
- Old Irish imb "butter" (vs. Breton aman(en)n, Cornish amanyn)
- Old Irish ingen "nail" (vs. Old Welsh eguin)
- Old Irish tengae "tongue" (vs. Welsh tafod)
- Old Irish ing "strait" (vs. Middle Welsh eh-ang "wide")
Insular Celtic as a language area 
In order to show that shared innovations are from a common descent it is necessary that they do not arise because of language contact after initial separation. A language area can result from widespread bilingualism, perhaps because of exogamy, and absence of sharp sociolinguistic division. In Post-Roman Britain Goidelic and Brythonic seem to have been of roughly equal status, with several Goidelic loan words in Brythonic and several Brythonic loan words in Old Irish. There is historical evidence of Irish in what are now Wales and England, as well as of Brythonic in Ireland, during this period. There is also archaeological evidence of substantial contact between Britain and Ireland in the Pre-Roman period and of Roman period contact.
Ranko Matasović has provided a list of changes which affected both branches of Insular Celtic but for which there is no evidence that they should be dated to a putative Proto-Insular Celtic period. These are:
- Phonological Changes
- The lenition of voiceless stops
- Morphological Changes
- Creation of conjugated prepositions
- Loss of case inflection of personal pronouns
- Creation of the equative degree
- Creation of the imperfect
- Creation of the conditional mood
- Morphosyntactic and Syntactic
- Rigidisation of VSO order
- Creation of preposed definite articles
- Creation of particles expressing sentence affirmation and negation
- Creation of periphrastic construction
- Creation of object markers
- Use of ordinal numbers in the sense of "one of".
Absolute and dependent verb 
The Insular Celtic verb shows a peculiar feature unknown in any other attested Indo-European language: verbs have different conjugational forms depending on whether they appear in absolute initial position in the sentence (Insular Celtic having verb–subject–object or VSO word order) or whether they are preceded by a preverbal particle. The situation is most robustly attested in Old Irish, but it has remained to some extent in Scottish Gaelic and traces of it are present in Middle Welsh as well.
Forms that appear in sentence-initial position are called absolute, those that appear after a particle are called conjunct (see Dependent and independent verb forms for details). The paradigm of the present active indicative of the Old Irish verb beirid "carry" is as follows; the conjunct forms are illustrated with the particle ní "not".
|1st person singular||biru "I carry"||ní biur "I do not carry"|
|2nd person singular||biri "you carry"||ní bir "you do not carry"|
|3rd person singular||beirid "s/he carries"||ní beir "she/he does not carry"|
|1st person plural||bermai "we carry"||ní beram "we do not carry"|
|2nd person plural||beirthe "you carry"||ní beirid "you do not carry"|
|3rd person plural||berait "they carry"||ní berat "they do not carry"|
In Scottish Gaelic this distinction is still found in certain verb-forms:
|cuiridh "puts/will put"||cha chuir "doesn't put/will not put"|
|òlaidh "drinks/will drink"||chan òl "doesn't drink/will not drink"|
|ceannaichidh "buys/will buy"||cha cheannaich "doesn't buy/will not buy"|
In Middle Welsh, the distinction is seen most clearly in proverbs following the formula "X happens, Y does not happen" (Evans 1964: 119):
- Pereid y rycheu, ny phara a'e goreu "The furrows last, he who made them lasts not"
- Trenghit golut, ny threingk molut "Wealth perishes, fame perishes not"
- Tyuit maban, ny thyf y gadachan "An infant grows, his swaddling-clothes grow not"
- Chwaryit mab noeth, ny chware mab newynawc "A naked boy plays, a hungry boy plays not"
The older analysis of the distinction, as reported by Thurneysen (1946, 360 ff.), held that the absolute endings derive from Proto-Indo-European "primary endings" (used in present and future tenses) while the conjunct endings derive from the "secondary endings" (used in past tenses). Thus Old Irish absolute beirid "s/he carries" was thought to be from *bʰereti (compare Sanskrit bharati "s/he carries"), while conjunct beir was thought to be from *bʰeret (compare Sanskrit a-bharat "s/he was carrying").
Today, however, most Celticists agree that Cowgill (1975), following an idea present already in Pedersen (1913, 340 ff.), found the correct solution to the origin of the absolute/conjunct distinction: an enclitic particle, reconstructed as *es after consonants and *s after vowels, came in second position in the sentence. If the first word in the sentence was another particle, *(e)s came after that and thus before the verb, but if the verb was the first word in the sentence, *(e)s was cliticized to it. Under this theory, then, Old Irish absolute beirid comes from Proto-Celtic *bereti-s, while conjunct ní beir comes from *nī-s bereti.
The identity of the *(e)s particle remains uncertain. Cowgill suggests it might be a semantically degraded form of *esti "is", while Schrijver (1994) has argued it is derived from the particle *eti "and then", which is attested in Gaulish.
Continental Celtic languages cannot be shown to have any absolute/conjunct distinction. However, they seem to show only SVO and SOV word orders, as in other Indo-European languages. The absolute/conjunct distinction may thus be an artifact of the VSO word order that arose in Insular Celtic.
Possible Afro-Asiatic substratum 
||An editor has expressed a concern that this article lends undue weight to certain ideas, incidents, controversies or matters relative to the article subject as a whole. (March 2010)|
The concept of the Insular Celtic languages being descended from Hebrew was part of Medieval superstition, but the hypothesis that they had features from an Afro-Asiatic substratum (Iberian and Berber languages) was first proposed by John Morris-Jones in 1900. Some well-known linguists have been adherents such as Julius Pokorny, Heinrich Wagner, and Orin Gensler. There has been further work on the theory by Shisha-Halevy  and Theo Vennemann.
However, the theory has been strongly criticised by Graham Isaac and by Kim McCone. Isaac considers the twenty points identified by Gensler as trivial, dependencies or vacuous. Thus he considers the theory to be not just unproven but wrong.
- Insular Celtic as a Language Area in The Celtic Languages in Contact, Hildegard Tristram, 2007.
- Appendix to The Welsh People by John Rhys and David Brymore-Jones
- Das nicht-indogermanische substrat im Irischen in Zeitschrift fur Celtische Philologie 16 and 19
- Gaeilge theilinn (1959) and subsequent articles
- A Typological Evaluation of Celtic/Hamito-Semitic Syntactic Parellels, University of California Press, 1993
- “Celtic Syntax, Egyptian-Coptic Syntax”, in: Das Alte Ägypten und seine Nachbarn: Festschrift Helmut Satzinger, Krems: Österreichisches Literaturforum, 245-302
- "Celtic and Afro-Asiatic" in The Celtic Languages in Contact (2007)
- The Origins and Development of Insular Celtic Verbal Complex (2006)
- Cowgill, Warren (1975). "The origins of the Insular Celtic conjunct and absolute verbal endings". In H. Rix (ed.). 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.
- 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.
- Schrijver, Peter (1995). Studies in British Celtic historical phonology. Amsterdam: Rodopi. ISBN 90-5183-820-4.
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