branch of the Indo-European language family, spoken throughout much of Western Europe in Roman and pre-Roman times and currently known chiefly in the British Isles and in the Brittany peninsula of northwestern France. On both geographic and chronological grounds, the languages fall into two divisions, usually known as Continental Celtic and Insular Celtic.

Continental Celtic is the generic name for the languages spoken by the people known to classical writers as Keltoi and Galatae; at various times during a period of roughly 1,000 years (approximately 500 BC–AD 500), they occupied an area that stretched from Gaul to Iberia in the south and Galatia in the east. The great bulk of evidence for Continental Celtic consists of the names of persons, tribes, and places recorded by Greek and Latin writers. Only in Gaul and in northern Italy are inscriptions found, and the interpretation of these is in most cases doubtful. Given the nature of the evidence, knowledge of these languages is confined largely to the sound system and a small part of the vocabulary, and no certain conclusions can be reached as to their historical development or the differences between them.

Insular Celtic refers to the Celtic languages of the British Isles, together with Breton (spoken in Brittany, France). As the name Breton implies, it is an importation from Britain and is not a Continental Celtic dialect. Although there is some scanty evidence from classical sources—mainly place-names—and a small body of inscriptions in the Latin and ogham alphabets from the end of the 4th to the 8th century AD, the main sources of information on the early stages of these languages are manuscripts written from the 7th century onward in Irish (Irish language) and somewhat later in the British languages.

The Insular languages fall into two groups—Irish and British. Irish (often called Goidelic (Goidelic languages), from Old Irish Goídel “Irishman,” or Gaelic, from Gael, the modern form of the same word) was the only language spoken in Ireland in the 5th century, the time when historical knowledge of that island begins. The two other members of this group, Scottish Gaelic (Scots Gaelic language) and Manx (Manx language), arose from Irish colonizations that began about that time. There were also important Irish-speaking colonies in Wales, but no trace of their language survives apart from a few inscriptions.

British (often called Brythonic (Brythonic languages), from Welsh Brython “Briton”) had almost the same degree of influence on the island of Britain and the Isle of Man. Inscriptions and personal names surviving from Scotland show clearly that there was a non-Indo-European language spoken there, usually called Pictish (Pictish language), which was later replaced by British. There were undoubtedly dialectal differences within the island, but the existing dialects arose from the fragmentation of British by the Irish invasions of Man and what is now Scotland and by the English invasions that began in what is now southern England and finally reached Scotland. Scotland has ever since been partitioned linguistically between English (or “Scots”) and Irish (or “Erse”—the Scots form of “Irish”—or “Gaelic”). A British dialect, now labeled Cumbric, lingered on in the western borderlands between England and Scotland until perhaps the 10th century, but almost nothing is known about it. In what is now Wales, British survived as the dominant language until a century or so ago; it is now known as Welsh. Another pocket of British speech survived in Cornwall until the end of the 18th century. It was from this area that emigrants in the 5th and 6th centuries AD had brought Celtic once more to the European mainland by establishing a colony in northwestern France, still called Brittany. It is just possible that there were some traces of the Continental Celtic language (i.e., Gaulish (Gaulish language)) at that time in this remote area, although Breton is too similar to Cornish (an Insular Celtic tongue) to suggest any serious influence from Gaulish.

The reconstruction of Common Celtic (or Proto-Celtic)—the parent language that yielded the various tongues of Continental Celtic and Insular Celtic—is of necessity very tentative. Whereas Continental Celtic offers plenty of evidence for phonology (the sound system), its records are too scanty to help much with the grammar (morphology or syntax), for which the best available evidence is Old Irish, the most archaic of the Insular languages. The records provide a picture of a language of the same type as Latin or Common Germanic; that is, one that still maintains a considerable part of the structure of the ancestral Indo-European language and has not lost final or medial syllables. Its vowel system differs only slightly from that reconstructed for Indo-European by the French linguist Antoine Meillet (Meillet, Antoine). Differences include the occurrence of Celtic *ī for Indo-European *ē (e.g., Gaulish rix and Irish rí, “king”; compare Latin rex) and *ā in place of *ō. (An asterisk 【*】 before a letter or word indicates that the sound or word is not attested but is a hypothetical, reconstructed form.)

The consonantal system, too, is conservative, although there are some striking features. Among them are the loss of *p (e.g., Irish athair “father”; cf. Latin pater) and the falling together of the aspirated and unaspirated voiced stops assumed for Indo-European. (A stop is a consonant made with complete momentary stoppage of the breath stream some place in the vocal tract; voiced stops are those produced with the vocal cords vibrating, such as b, d, g. An aspirated sound is accompanied by a puff of breath, often written as an h, as in bh, dh, gh; an unaspirated consonant lacks this accompanying puff of breath.) Thus, Old Irish dán “what is given” corresponds to Latin donum “gift” (from Indo-European *d), but Old Irish de-naid “sucks” corresponds to Latin fe- in fe-mina, fe-llare (from Indo-European *dh). This loss of distinctive aspiration occurs with three out of the four voiced stops, a situation close to that of Slavic.

Other considerations, however, show that Celtic belongs to the so-called southern group of the European branch of Indo-European languages, or in another classification, to the same centum group as Latin, whereas Slavic belongs to the satem group. (The centum and satem divisions of Indo-European languages are made according to the treatment of certain sounds, called palatals, that existed in the ancestral Indo-European language.)

The loss of *p in Celtic was very early; only the place-name Hercynia, preserved in Greek, shows that, in initial position, it became an h sound before disappearing. In most of the known Celtic languages, a new p sound has arisen as a reflex of the Indo-European *k^w sound. Thus there is Gaulish pempe, Welsh pimp “five,” compared to Old Irish cóic and Latin quinque “five.” The Irish evidence shows that *k^wenk^we must be reconstructed as the form in Common Celtic. The terms P-Celtic and Q-Celtic are sometimes used to describe assumed divisions of Common Celtic; to use one sound shift to distinguish dialects is, however, hardly justified, and the classification will not be used in this article.

The morphology (structure) of nouns and adjectives shows no striking changes from Indo-European. The Irish verb, however, exhibits a remarkable archaism not found in any other recorded Indo-European language. It has recently been demonstrated that the so-called primary and secondary endings of the Indo-European verb, as in the 3rd person singular endings *-(e)t and -(e)ti, both occurred in the same tense. The forms with *-i were used when the verb had absolute initial position; those without it were used in the normal verbal position at the end of the sentence. This is reflected in the Old Irish forms beirith (from *bereti) “he bears” and ní beir (from *beret) “he does not bear.” It cannot be stated with certainty that Continental Celtic had preserved such forms. The Continental Celtic dialects show a few cases of sentences—admittedly imperfectly understood—in which the verb appears to be placed after the subject and before the object, as in modern western European languages. The history of Insular Celtic, however, shows a gradual shift from the older final position of the verb to the initial position, a position that has now become regular in all of the languages.

The question of the relationship of Common Celtic to the other Indo-European languages remains open. For some time, it was held that Celtic stood in an especially close relation to the Italic branch; some scholars even spoke of a period when an Italo-Celtic “nation” existed, toward the end of the 2nd millennium BC. The existence of a q–p relationship (see above) inside Italic too (e.g., Latin quattuor “four,” but Oscan petora) was thought by some to support this view. Much of this argument is, however, based on accidental resemblances (e.g., the Irish future tense in f- and the Latin future in b-) or on formations such as the deponent and passive verb forms ending in -r, which at one time were known mainly in Italic and Celtic but have since been found in the Hittite and Tocharian languages as well. The undeniable common features between Celtic and Italic, such as the superlative endings of adjectives (Latin -issimus; Celtic *-samos, *-isamos), are hardly sufficient to justify the assumption of a special relationship, and the whole concept of an Italo-Celtic unity has been powerfully criticized by the linguists Carl J.S. Marstrander and Calvert Watkins.

The original home of the Celts cannot be located precisely, but, on the whole, the evidence points to the eastern part of central Europe. There is more evidence for their contacts with other Indo-European peoples. One group of Celts, at least, found themselves neighbours of the Germanic peoples and were often confused with them by classical writers. It can be inferred that the Celts had attained a higher standard of social organization than the Germanic peoples from the existence of words such as Gothic reiki and andbahts (modern German Reich, Amt), apparently borrowed from Celtic *rīgion “kingdom” and *ambactos “officer.” To the Greeks and Romans, on the other hand, the Celts were inferior in culture; Celtic words in Greek are restricted to those describing Celtic institutions, such as bardoi “poets.” The borrowings from Celtic into Latin (Latin language), which derive mainly from the period before the expansion of Roman power, belong to a few restricted categories, such as war (lancea “lance”), transport (carrus “baggage wagon” and carpentum “light carriage”), and agricultural products (cervesia “beer”). When the Romans finally conquered Gaul and imposed their language, a number of Celtic words came into Latin, but the Celtic terms were mainly concerned with rural life. These are more common in French dialects than in standard French, which preserves a mere handful, such as mouton “sheep,” ruche “beehive,” and arpent “land measure.”

Celtic died out very quickly in eastern Europe. In its farthest outpost in Asia Minor, it may be assumed that the Letter of Paul to the Galatians was addressed to a people whose culture was already Greek but whose Celtic origins are clear from names preserved by classical authors; e.g., Drunemeton “the very sacred place,” formed from two distinctively Celtic elements. When commenting on that Letter, St. Jerome (Jerome, Saint) (died AD 419/420) said that the Galatians still spoke a language almost the same as that of the people of Trier. As he had been in both places, his evidence cannot be dismissed offhand, and it may be that a few speakers of Celtic still existed in both areas. Since St. Jerome did not claim to know any Celtic dialect, however, his statement cannot be accepted with certainty. Speaking generally, the history of Continental Celtic comes to an end as that of Insular Celtic begins.

The earliest evidence for Insular Celtic consists, like that for Continental Celtic, mainly of names recorded by Greek and Latin authors. In the case of Ireland, these were entirely by hearsay, and many of the Irish place-names recorded by Ptolemy in the 2nd century AD have not yet been identified. From perhaps the 4th century, ogham (ogham writing) inscriptions (see alphabet) are found in Ireland, consisting almost entirely of personal names. From the 5th century onward, British names in Latin inscriptions are recorded in Wales, as well as Irish names in both Latin and ogham alphabets in areas of Irish settlement. These scanty records are of value above all in establishing that, up to very nearly the time at which written documents become available, British and Irish had remained similar in structure to Gaulish. Thus, in Britain is found the genitive (possessive form) Catotigirni, which in Old Welsh gives Cattegirn, and in Ireland the genitive Dovatuci exists, which in Old Irish gives Dubthaich. These changes—loss of final syllables and connecting vowels, weakening of consonants between vowels, and so on—are very similar to what was happening to Latin in France at the same time; e.g., Latin avicellus and aqua finally became oiseau and eau. There is no satisfactory explanation of why these profound changes should have occurred at this time, nor can the period at which they occurred be fixed precisely, for the engravers of the inscriptions clearly went on using traditional forms long after the sound had changed.

The new languages, the only forms of Celtic that are known thoroughly, present a considerable number of unusual features, some of them unknown to other Indo-European languages. Some scholars have argued that these features may have resulted from the presence of a large non-Celtic substratum in the British Isles. Because it is hardly likely that the Celtic invasions of those islands began much before 500 BC or that the invaders exterminated the existing inhabitants, such a possibility cannot be denied. On the other hand, some features once thought to be exotic, such as the initial position of the verb in the sentence, have been convincingly demonstrated to be organic developments from Indo-European. Others, such as the system of counting by 20s, are clearly innovations, but this system is shared by English (“three score and ten”), French (quatre-vingts “80”), and Danish, in all of which it is also an innovation, as well as Basque (Basque language), in which it appears to be old.

The most remarkable phonological feature of Insular Celtic is the development of a double series of consonants (consonant) in which strongly articulated consonants are distinguished from their weak counterparts. The two series were originally merely phonetic variants, with the strong variety occurring in absolute initial position and in certain consonant clusters and the weak elsewhere. Later, however, the two series became independent, or phonological. In the languages as they first appear in writing, considerable changes have taken place in the phonetic forms of the two series. Both in Irish and in Welsh, Cornish, and Breton, the opposition (contrast) of strong:weak in the voiced stops has been replaced by stop:spirant (e.g., b:v). (A spirant, such as v, f, s, is produced with local friction and without complete stoppage of the breath stream.) Irish has the same system for the unvoiced stops (e.g., t:th), but Welsh, Cornish, and Breton have voicing in this instance (e.g., voiceless t:voiced d). These changes by themselves are not very different from the weakening of consonants between vowels that occurs in other western European languages (compare Welsh pader “prayer,” a loanword from Latin pater “father,” with Spanish padre “father,” deriving from Latin patrem), but, in Insular Celtic, they occurred not only inside the word but also inside the phrase, so that the initial consonant of a word preceded by another word ending in a vowel was weakened. When the final syllables were lost in the evolution to the modern languages, these variations remained, and a system of initial mutations (changes) was thus set up. If, for example, a Goidelic nominative form *sindos kattos koilos “the thin cat” is reconstructed, this will give Old Irish in catt coel after the loss of final syllables, but the genitive *sindī kattī koilī “of the thin cat” will give in chaitt choíl with changed initial consonants. The same sort of change occurred in one Italian dialect: in Tuscan, there occur porta “door,” la forta “the door,” tre porte “three doors,” from Latin porta, illa porta, tres portae. In both cases, consonant weakening has spread from word to sentence; there is a common development, but it cannot be claimed that it is distinctively Celtic.

Another feature of Insular Celtic is its lack of the infinitive form of the verb found in most other Indo-European languages—e.g., English “to do,” “to call.” The equivalent is the verbal noun, which is a noun closely linked to the verb, though not necessarily derived from the same stem. Being a noun, it can have a following noun in the genitive case, which, in the older languages at least, is subjective or objective according to whether the verb with which it is linked is intransitive or transitive. Thus, from the Old Irish sentence téit in ben “the woman goes,” the verbal noun phrase techt inna mná “the coming of the woman” can be derived, whereas from marbaid in mnaí “he kills the woman” can be formed marbad inna mná (lais) “the killing of the woman (by him).” Among many other functions of the verbal noun is its use, when preceded by the appropriate preposition, with the substantive verb to provide a tense with continuous meaning. Thus, to téit in ben there is a parallel a-tá in ben oc techt “the woman is at going” (= “the woman is going”), and to marbaid in mnaí corresponds a-tá oc marbad inna mná “he is killing the woman.” The close resemblance of this system to that of modern English, in which it is a comparatively recent development, has been variously explained as the working of a substratum or, more recently, in terms of areal (regional) development.

The discussion of the individual languages that follows divides them into the two main groups, beginning with Irish (Irish language), which is the oldest attested.

The history of Irish may be divided into four periods: that of the ogham inscriptions, probably AD 300–500; Old Irish, 600–900; Middle Irish, 900–1200; and Modern Irish, 1200 to the present. This division is necessarily arbitrary, and archaizing tendencies confuse the situation, especially during the period 1200–1600, when a highly standardized literary norm was dominant. After 1600, the modern dialects, among them Scottish Gaelic and Manx, begin to appear in writing.

The Latin alphabet was introduced into Ireland by British missionaries in the 5th century and soon began to be used for writing Irish. By the middle of the 6th century, the process of putting into literary form the rich oral tradition of the native learned class was certainly well advanced. The problems of interpreting the early writings are complicated by the fact that the orthography was based on that of Latin, but with a British pronunciation; e.g., Latin pater was read as pader, the form of the loanword in Modern Welsh, and Old Irish Pátric was read as Pádraig (as it is spelled in Modern Irish). No new letters were evolved; the weak (less forceful) consonants were distinguished only in instances in which there were Latin spellings that could be utilized (e.g., strong ll: weak l, strong rr: weak r, nn:n, c:ch, t:th) or with the help of the punctum delens (s:ṡ, f:ḟ), a dot that shows that the sound is not pronounced. As a result, many ambiguities remain: ní beir can mean either “he does not carry” or “he does not carry it,” according to whether the b- is read as a b sound or a v sound. Nor was the Latin alphabet capable of dealing with the new system of consonant quality that appears in Irish alone among the Celtic languages. Thus, from the Celtic nominative singular and plural forms bardos, bardī developed Welsh bardd, plural beirdd, with a vowel alternation like that of English “mouse, mice.” In Irish, the forms are bard, baird; the -i- of baird is purely graphic, serving to indicate that the following consonants are both palatalized. (Palatalized consonants are those in which the pronunciation is modified by raising the tongue toward the hard palate.) This palatalization had been purely phonetic as long as the -ī that caused it survived, but in Old Irish the palatalization became independent, so that each consonant of Common Celtic evolved into four distinct consonants (i.e., phonemes); for example, from original Common Celtic b are derived a b sound and a palatalized b sound, and a v sound and a palatalized v sound.

Apart from these phonetic developments, Old Irish is striking chiefly for the extraordinary proliferation of particles that appear before the verb and are used in forming compound verbs. For example, the Latin word suffio “I fumigate” is translated as fo-timmdiriut, composed of fo “under,” to “to,” imb- “around,” di “from,” and the stem reth- “run,” with vowel and consonant changes appropriate to the 1st person singular present tense. Such forms, combined with a system of infixed accusative and dative pronouns (i.e., pronouns inserted within a word) and syntactical accent shifts, produced a verbal system almost as complicated as that of Basque, though transparently Indo-European in origin. This system began to break down during the Old Irish period; the process was no doubt accelerated by the Viking raids that began at the end of the 8th century and that disrupted the monastic system, the guardian of the literary norm of Old Irish. Popular forms broke through in the Middle Irish period, though always mixed with archaizing forms; the backward-looking Irish scribes were never content to write down their own vernacular. During the 12th century, many ecclesiastical synods were held with the object of bringing the organization of the Irish Church more closely into line with that of western Europe, and the Anglo-Norman invasion took place in the latter part of the same century. It may have been these far-reaching changes that inspired the Irish literati to undertake a new standardization of their language. From the beginning of the 13th century, there is a rigidly fixed norm, often called Classical Modern Irish, which, for over four centuries, was used as the exclusive literary medium in Ireland and in Gaelic-speaking Scotland (there is no evidence for the Isle of Man).

The Scandinavians were first contained and then absorbed; they contributed a small number of loanwords to Irish, mainly in the field of navigation but also in that of urban life, for they were the first to establish towns in Ireland, though only on the coast. The Anglo-Normans were a more serious problem. After almost complete success in the early period, however, they became largely Gaelicized in custom and language outside the towns they had founded. They contributed a large number of loanwords to Irish in the fields of warfare, architecture, and administration, though many of these were comparatively short-lived. When English took over from Anglo-Norman as the language of administration and English colonies began to be planted in Ireland, English loanwords began to come into Irish. Few of these, however, were recognized in the literary language, and only from the evidence of the modern dialects has it become clear that they were quite numerous.

It was not until the beginning of the 17th century that the English power was finally consolidated in Ireland, first by military conquest and later by the planting of English-speaking colonists on a much larger scale than before. From this time onward, the decline of Irish began, with Irish becoming the language of an oppressed people. With no schools to teach the literary language nor any native nobility to support the literati who used it, the dialects appeared for the first time and began to be written in the paper manuscripts that constituted almost the only form of publishing available to those using Irish. By the beginning of the 19th century, it is probable that the population was almost equally divided between Irish speakers, mainly in the western half, and English speakers, mainly in the eastern half. The real imbalance lay in the fact that many of the Irish speakers were bilingual, whereas few of the English speakers were. The first census to record language use was taken in 1851, after the great famine that had struck the western areas with exceptional severity. By this time, the total number of Irish speakers was 1,524,286 (23 percent of the population), but only 319,602 spoke Irish (Irish literary renaissance) exclusively. The decline of Irish (Irish language) has continued to the present day, in spite of a revival campaign initiated by the Gaelic League in 1893 and made part of official policy after the establishment of the Irish Free State in 1921.

Since then, Irish has been recognized as the first official language of the state; it is a compulsory subject in all of the schools and is a requirement for civil service and some other posts. There are probably more people able to read Irish—perhaps 300,000—than there ever were before. From 1945 onward, a standard written language has evolved, and there is a small but flourishing literary movement. Nearly all of the readers of Irish are English speakers by upbringing, however, and not many of them would claim that Irish had become their main language. In the western areas in which Irish was the traditional speech, there are now fewer than 50,000 people to whom it is a mother tongue, and all but a handful of these have a more or less adequate command of English.

Some aspects of the modern Scottish Gaelic dialects show that they preserve features lost in the language of Ireland during the Old Irish period; such archaism is characteristic of “colonial” languages. The innovations are, however, more striking than the archaisms. Most remarkable is the loss of the voicing feature (i.e., the vibration of the vocal cords) in the stops. All of the stopped consonants are unvoiced, and the original voiceless stops have become strongly aspirated; for example, the equivalent of Irish bog “soft” is 【pok】, p being the voiceless counterpart of b, and that of cat “cat” is 【k^haht】, the superscript ^h after k indicating the aspirated quality. (The brackets indicate that the symbols printed within them are phonetic rather than orthographic.)

Scottish Gaelic was planted on British soil, and the verbal system has been remolded on the lines of the British language, which originally had no future tense. As in Modern Welsh, the inherited present tense has largely future meaning, and present time is mainly expressed by the present-tense form of the substantive verb and the preposition a(ig) with the verbal noun. (In Insular Celtic, there are two verbs for “to be,” a substantive verb with the meaning, roughly, “to exist,” and a linking verb such as “is” in “John is a boy” or “sky is blue.”) Thus, from Old Irish téit in ben “the woman goes” is derived Scottish Gaelic théid a' bhean “the woman will go,” and from Old Irish a-tá in ben oc techt “the woman is going” results the Scottish Gaelic form thà an bhean a' dol “the woman goes” or “the woman is going.”

It is only from the 17th century onward that the development of Scottish Gaelic can be studied, for, up until then, Classical Modern Irish was the literary norm. Indeed, the first book to be printed in Irish was a translation of the Calvinist Book of Common Order, published in Edinburgh in 1567, and the Scottish Reformers used the Irish Bible for some time, until it became clear that it was too foreign for the people to understand. A native Scottish standard emerged gradually during the 17th century, as poets ignorant of the Irish norm began to compose in their native dialects. It was not until the 18th century that the orthography became more or less fixed, and, until recent reforms in Ireland, the divergencies between the written languages were comparatively small. It is clear, however, that Scottish Gaelic must now be regarded as a separate language, though the differences between it and Irish are no greater than those between standard German and the Swiss dialects.

Scottish Gaelic was confronted by northern dialects of English (Scots) from the very beginning; these rapidly penetrated into the east of the country, especially in the area centred on Edinburgh, the capital. The so-called Highland Line, marking the boundary between the two languages, has been steadily receding to the west since medieval times. By 1901, there were 230,806 speakers of the language, including 28,106 who spoke Scottish Gaelic exclusively; 106,466 persons, including nearly all of the monolingual Scottish Gaelic people, lived in the two counties of Inverness and Ross (Ross and Cromarty). The decline has continued steadily, and, even in those two counties, Gaelic is rapidly disappearing from the mainland, though it is holding its ground well in the Hebrides. Scottish Gaelic speakers in the early 1980s numbered about 90,700, which shows that the state of Scottish Gaelic survival is in many ways less serious than that of Irish. Because the majority of Gaelic speakers are Protestants who are accustomed to reading the Bible and using the vernacular in their religious services, literacy in Gaelic has been widespread. Furthermore, however low the census figures may be, they give an accurate picture of the number of those to whom Gaelic is a mother tongue because the number of English speakers who have acquired it is negligible. It must be admitted, however, that the recent literary revival finds its audience among the displaced Gaelic speakers of Edinburgh and Glasgow rather than in the Hebrides, where Gaelic is still confined to the home and English is the language of culture. In addition, there were about 500 Gaelic speakers in Nova Scotia in the early 1980s.

The history of the Isle of Man (Man, Isle of) is imperfectly known. It was first inhabited by British speakers, then colonized from Ireland, and later became part of the Scandinavian Lordship of the Isles until 1266, when the King of Norway ceded both Man and the Hebrides to Scotland. From then on, it became involved in the wars between England and Scotland until 1346, when it passed finally to England. Though an Irish dialect survived as the speech of the majority of the people, these circumstances were not propitious for literary contacts with Ireland, and Manx was apparently not written until the Welsh bishop John Phillips translated the Anglican Book of Common Prayer in 1610, using an orthography based on that of English. This orthography makes Manx difficult to understand for readers of Irish and Scottish Gaelic, to whom it is of considerable interest because it represents a dialect entirely free of literary influences. The orthography soon became fixed, and a far-reaching series of later phonetic changes made the written form a highly inaccurate representation of the final stages of the language. Phonologically, it has more in common with the eastern dialects of Irish than with Scottish Gaelic, but its morphology and syntax are much more like those of Scottish Gaelic, probably because of the common British substratum. Its tense system is similar to that of Scottish Gaelic and Welsh, and its use of periphrastic verb forms (i.e., longer forms with several elements) with the auxiliary meaning “to do” goes further than either of these, especially in its final stages.

In the beginning of the 18th century, English was still not understood by most of the people, but during the 19th century the decline of Manx was rapid, and the census of 1901 showed only 4,419 speakers of the language, all bilingual. Twenty years later, the language had ceased to be used as a normal means of communication, but, until recently, investigators have been able to find old people capable of giving useful information.

Britain was thoroughly romanized, and it is clear that the British language itself had been much affected by Latin (Latin language); on the level of vocabulary, such an everyday word as Welsh pysg “fish,” for example, derives from Latin piscis. The vowel system lost independent vowel quantity, the length of vowels becoming determined by the structure of the syllable, a situation that also occurred when the later Latin developed into Romance. Even after the collapse of Roman rule, Latin retained the same prestige among British Christians that it had in the rest of the Western Empire. The Irish monks introduced to the British speakers the custom of writing down the vernacular language at about the end of the 8th century; they adapted the clumsy Irish orthography for that purpose. At this period, the British dialects were very close to one another and can hardly be classed as separate languages, though they soon began to diverge. Like Old Irish, they had lost their final syllables and had undergone many other changes from the state shown by the inscriptions. Notably, the languages show only the merest traces of the declension of the noun, although the verb preserves a full inflectional system (that is, it has a full series of endings). It is clear that no future tense existed in early British, though the separate languages were later to fill this gap by various means.

Welsh is the earliest and best attested of the British languages. Although the material is fragmentary until the 12th century, the course of the language can be traced from the end of the 8th century. The earliest evidence may represent the spoken language fairly accurately, but a poetic tradition was soon established, and by the 12th century there was a clear divergence between the archaizing verse and a modernizing prose. The latter was characterized by a predominance of periphrastic verbal-noun constructions at the expense of forms of the finite verb. By this time, too, the forms corresponding to other Celtic and Indo-European present-tense forms had largely acquired future meaning; e.g., Welsh nid â “he will not go” (future) contrasts with Irish ní aig “he does not drive” (present). The gap thus left was filled, as in Scottish Gaelic and Manx, by a construction involving the substantive verb and the verbal noun; e.g., y mae'r wraig yn myned “the woman goes” or “the woman is going” is composed of the verb mae “is” and the verbal noun myned “going.”

By the 14th century, prose and verse styles became more similar, the prose being less colloquial and the verse less archaic. This marks the beginning of modern literary Welsh, which was finally fixed by the Bible translation of 1588. Modern literary Welsh developed at a time when Welsh national identity was beginning to be seriously threatened by the close relations with England that followed on the accession of the Welshman Henry Tudor ( Henry VII) to the English throne in 1485. Welsh was being written less and less, and the spoken language was being penetrated by English words. In 1536, the Act of Union deprived Welsh of its official status. By the beginning of the 18th century, the position of the Welsh language had fallen very low, though it was still the vernacular of the vast majority of the people. It was saved by the Methodist revival of the 18th century, which established schools everywhere to teach the people how to read the Welsh Bible and which brought the Bible itself, together with Welsh religious books, into almost every home. The literary language rejected most of the English loanwords that had come into the popular speech, and, by the 19th century, a highly literate Wales was equipped with reading material of every kind in the Welsh language. Meanwhile, however, the popular speech diverged further from the fixed literary norm, which was never spoken except in the pulpit or on the platform. Modern Wales has a literary language that no mother speaks to her child and widely differing dialects that appear in print only to represent dialogue in stories and novels.

The Industrial Revolution of the 19th century first undermined the dominance of Welsh in Wales: English-speaking workers were brought into the mines and factories in such numbers that they could not be absorbed linguistically. By 1901 English speakers outnumbered Welsh speakers for the first time. Out of a population of 2,012,876, only 929,824 were reported as Welsh-speaking, though 280,985 people spoke Welsh alone. By the early 1980s the number of Welsh speakers had dropped to about 395,000, representing about 14 percent of an increased population. Most of rural Wales, however, is still Welsh speaking, and recent years have seen a great improvement in the official status of Welsh and a considerable increase in its use in the schools; it is certainly the most firmly rooted of the modern languages of Celtic origin.

In addition, there are still about 8,000 Welsh speakers in parts of Patagonia, Argentina, which was colonized by Welsh settlers in 1865. These people maintain cultural contacts with the homeland but are all bilingual in Welsh and Spanish and seem fated to final assimilation.

Breton disappeared from sight after the early period, and no literary texts are available until the 15th century. These, mainly mystery plays (mystery play) and similar religious material, are written in a standardized language that is by now completely differentiated from Welsh and, to a lesser degree, from Cornish. The divergence between Breton and Cornish is largely a matter of the English loanwords in Cornish and the French loanwords in Breton. The present tense was retained in its original function, whereas a future and conditional were formed from the present and past subjunctive, respectively. Later, the Breton dialects became written and showed considerable divergencies in this form. Not until the 1920s was an attempt at standardization made, and even then it was necessary to adopt two norms. One was called KLT, from the initials of the Breton names of the dioceses of Cornouaille, Léon, and Tréguier, the dialects of which agree with Welsh and Cornish in having the stress accent on the next to the last syllable. The other norm was the dialect of Vannes in the south, which has the stress accent on the final syllable and many other distinctive features, at least some of which can be explained by its close contacts with French. More recently, two norms have been evolved to cover all four dialects; one of these is used by most writers, whereas the other is officially recognized by the universities of Brest and Rennes, in both of which Breton is taught.

Up until recently, Breton was the common language of the people in Cornouaille, Léon, Tréguier and Vannes, within the boundaries of the départements of Côtes-du-Nord, Finistère, and Morbihan. Breton may still have more speakers than Welsh, but this is quite uncertain because no language statistics exist for France. There is, however, general agreement that very few children today are being brought up speaking Breton. This is at least partly the result of French official policy, which in effect excludes the language from primary and secondary schools, though the poor economic opportunities in Brittany also play a part. The literary movement is, therefore, confined to an intelligentsia of perhaps not much more than 10,000 people, many of whom live outside Brittany. The overwhelming mass of the remainder of Breton speakers are literate only in French, and chances for the survival of Breton seem very poor.

Like Breton, Cornish had no literary texts before the 15th century. Those that exist are mainly mystery plays, some of which are almost literal translations from English. Cornish is much closer in structure to Breton than to Welsh, but it has also been heavily influenced by English. At the beginning of the 18th century, there were still a number of areas in which Cornish was spoken, but it died out as a means of communication by the end of the century.