Girish Mahajan (Editor)

Old Irish

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Writing system

Early form
Primitive Irish

Ireland, Isle of Man, western coast of Great Britain

6th century–10th century; evolved into Middle Irish about the 10th century

Language family
Indo-European Celtic Insular Celtic Goidelic Old Irish

Old Irish (Old Irish: Goídelc; Irish: Sean-Ghaeilge; Scottish Gaelic: Seann Ghàidhlig; Manx: Shenn Yernish; sometimes called Old Gaelic) is the name given to the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from c.600 to c.900. The primary contemporary texts are dated c.700–850; by 900 the language had already transitioned into early Middle Irish. Some Old Irish texts date from the 10th century, although these are presumably copies of texts composed at an earlier time period. Old Irish is thus the ancestor of Modern Irish, Manx, and Scottish Gaelic.


Old Irish is known for having a particularly complex system of morphology and especially of allomorphy (more or less unpredictable variations in stems and suffixes in differing circumstances) as well as a complex sound system involving grammatically significant consonant mutations to the initial consonant of a word. Initial consonant mutation must have been present in at least late Common Celtic (Proto-Celtic) because this distinguishing feature has survived with grammatical significance in both modern Welsh and Breton, and the extinct Cornish language also featured. Because the languages belong to the Brittonic branch of the Celtic language group (so-called "P-Celtic"), initial mutation must predate the split in the development paths of the Brittonic and Goidelic languages. No mutations are, however, attested in Gaulish material so a parallel evolution of the phenomenon in the neo-Celtic languages is also possible. Much of the complex allomorphy has been lost, but the rich sound system has been maintained, with little change, in the modern languages.

Contemporary Old Irish scholarship is still greatly influenced by the works of a small number of scholars active in the late 19th and early 20th centuries such as Rudolf Thurneysen (1857–1940) and Osborn Bergin (1873–1950).

Notable characteristics

Notable characteristics of Old Irish compared with other old Indo-European languages, are:

  • Initial mutations, including lenition, nasalisation and aspiration/gemination.
  • A complex system of verbal allomorphy.
  • A system of conjugated prepositions that is unusual in Indo-European languages (although they are found in many Semitic languages such as Arabic): dím "from me", dít "from you", de "from him", di "from her", diib "from them" (basic preposition di "from"). There is a great deal of allomorphy here, as well.
  • Infixed object prepositions, which are inserted between the verb stem and its prefix(es). If a verb lacks any prefixes, a dummy prefix is normally added.
  • Special verbal conjugations are used to signal the beginning of a relative clause
  • Old Irish also preserves most aspects of the complicated Proto-Indo-European (PIE) system of morphology. Nouns and adjectives are declined in three genders (masculine, feminine, neuter); three numbers (singular, dual, plural); and five cases (nominative, vocative, accusative, dative and genitive). Most PIE noun stem classes are maintained (o-, yo-, ā-, -, i-, u-, r-, n-, s-, and consonant stems). Most of the complexities of PIE verbal conjugation are also maintained, and there are new complexities introduced by various sound changes (see below).


    Old Irish was the only member of the Goidelic/Gaelic branch of the Celtic languages, which is, in turn, a subfamily of the wider Indo-European language family that also includes the Slavonic, Italic/Romance, Indo-Aryan and Germanic subfamilies, along with several others. Old Irish is the ancestor of all modern Goidelic languages: Modern Irish, Scottish Gaelic and Manx.

    A still older form of Irish is known as Primitive Irish. Fragments of Primitive Irish, mainly personal names, are known from inscriptions on stone written in the Ogham alphabet. The inscriptions date from about the 4th to the 6th centuries. Primitive Irish appears to have been very close to Common Celtic, the ancestor of all Celtic languages, and it had a lot of the characteristics of other archaic Indo-European languages.


    The consonant inventory of Old Irish is shown in the chart below. The complexity of Old Irish phonology is from a four-way split of phonemes inherited from Primitive Irish, with both a fortis–lenis and a "broad–slender" (velarised vs. palatalised) distinction arising from historical changes. The sounds /f v θ ð x ɣ h ṽ n l r/ are the broad lenis equivalents of broad fortis /p b t d k ɡ s m N L R/; likewise for the slender (palatalised) equivalents. (However, most /f fʲ/ sounds actually derive historically from /w/.)

    Some details of Old Irish phonetics are not known. /sʲ/ may have been pronounced [ɕ] or [ʃ], as in Modern Irish. /hʲ/ may have been the same sound as /h/ or /xʲ/. The precise articulation of the fortis sonorants /N/, /Nʲ/, /L/, /Lʲ/, /R/, /Rʲ/ is unknown, but they were probably longer, tenser and generally more strongly articulated than their lenis counterparts /n/, /nʲ/, /l/, /lʲ/, /r/, /rʲ/, as in the Modern Irish dialects (Connacht Irish) that still possess a four-way distinction in the coronal nasals and laterals. /Nʲ/ and /Lʲ/ may have been pronounced [ɲ] and [ʎ] respectively. The difference between /R(ʲ)/ and /r(ʲ)/ may have been that the former were trills while the latter were flaps. /m(ʲ)/ and /ṽ(ʲ)/ were derived from an original fortis–lenis pair.


    Old Irish had distinctive vowel length in both monophthongs and diphthongs. Short diphthongs were monomoraic, taking up the same amount of time as short vowels, while long diphthongs were bimoraic, the same as long vowels. (This is much like the situation in Old English but different from Ancient Greek whose shorter and longer diphthongs were bimoraic and trimoraic, respectively: /ai/ vs. /aːi/.) The inventory of Old Irish long vowels changed significantly over the Old Irish period, but the short vowels changed much less.

    The following short vowels existed:

    1The short diphthong ŏu may have existed very early in the Old Irish period/but not later on.

    Archaic Old Irish (before about 750) had the following inventory of long vowels:

    1Both /e₁ː/ and /e₂ː/ were normally written é but must have been pronounced differently because they have different origins and distinct outcomes in later Old Irish. /e₁ː/ stems from Proto-Celtic *ē (< PIE *ei), or from ē in words borrowed from Latin. e₂ː generally stems from compensatory lengthening of short *e because of loss of the following consonant (in certain clusters) or a directly following vowel in hiatus. It is generally thought that /e₁ː/ was higher than /e₂ː/. Perhaps /e₁ː/ was [eː] while /e₂ː/ was [ɛː]. They are clearly distinguished in later Old Irish, in which /e₁ː/ becomes ía (but é before a palatal consonant). /e₂ː/ becomes é in all circumstances. Furthermore, /e₂ː/ is subject to u-affection, becoming éu or íu, while /e₁ː/ is not.

    2A similar distinction may have existed between /o₁ː/ and /o₂ː/, both written ó, and stemming respectively from former diphthongs (*eu, *au, *ou) and from compensatory lengthening. However, in later Old Irish both sounds appear usually as úa, sometimes as ó, and it is unclear whether /o₂ː/ existed as a separate sound any time in the Old Irish period.

    3/ou/ existed only in early archaic Old Irish (c.700 or earlier); afterwards it merged into /au/. Neither sound occurred before another consonant, and both sounds became ó in later Old Irish (often ú or u before another vowel). The late ó does not develop into úa, suggesting that áu > ó postdated ó > úa.

    Later Old Irish had the following inventory of long vowels:

    1Early Old Irish /ai/ and /oi/ merged in later Old Irish. It is unclear what the resulting sound was, as scribes continued to use both and to indicate the merged sound. The choice of /oi/ in the table above is somewhat arbitrary.

    The distribution of short vowels in unstressed syllables is a little complicated. All short vowels may appear in absolutely final position (at the very end of a word) after both broad and slender consonants. The front vowels /e/ and /i/ are often spelled ae and ai after broad consonants, which might indicate a retracted pronunciation here, perhaps something like [ɘ] and [ɨ]. All ten possibilities are shown in the following examples:

    The distribution of short vowels in unstressed syllables, other than when absolutely final, was quite restricted. It is usually thought that there were only two allowed phonemes: /ǝ/ (written a, ai, e or i depending on the quality of surrounding consonants) and /u/ (written u or o). The phoneme /u/ tended to occur when the following syllable contained an *ū in Proto-Celtic (for example, dligud /ˈdʲlʲiɣuð/ "law" (dat.) < PC *dligedū), or after a broad labial (for example, lebor /ˈLʲevor/ "book"; domun /ˈdoṽun/ "world"). The phoneme /ǝ/ occurred in other circumstances. The occurrence of the two phonemes was generally unrelated to the nature of the corresponding Proto-Celtic vowel, which could be any monophthong: long or short.

    Long vowels also occur in unstressed syllables. However, they rarely reflect Proto-Celtic long vowels, which were shortened prior to the deletion (syncope) of inner syllables. Rather, they originate in one of the following ways:

  • from the late resolution of a hiatus of two adjacent vowels (usually as a result of loss of *s between vowels);
  • from compensatory lengthening in response to loss of a consonant (cenél "kindred, gender" < *cenethl; du·air-chér "I have purchased" < *-chechr, preterite of crenaid "buys");
  • from assimilation of an unstressed vowel to a corresponding long stressed vowel;
  • from late compounding;
  • from lengthening of short vowels before unlenited /m, N, L, R/, still in progress in Old Irish (compare erríndem "highest" vs. rind "peak").
  • Stress

    Stress is generally on the first syllable of a word. However, in verbs it occurs on the second syllable when the first syllable is a clitic (the verbal prefix as- in as·beir /asˈberʲ/ "he says"). In such cases, the unstressed prefix is indicated in grammatical works with a following centre dot (·).


    As with most medieval languages, the orthography of Old Irish is not fixed, so the following statements are to be taken as generalisations only. Individual manuscripts may vary greatly from these guidelines.

    The Old Irish alphabet consists of the following eighteen letters of the Latin alphabet:

    a, b, c, d, e, f, g, h, i, l, m, n, o, p, r, s, t, u

    In addition, the acute accent and the superdot are used as diacritics with certain letters:

  • The acute accent indicates a long vowel. The following are long vowels: á, é, í, ó, ú.
  • The superdot indicates the lenition of f and s: is silent, is pronounced /h/
  • The superdot is also sometimes used on m and n, with no change in pronunciation, when these letters are used to mark the nasalisation mutation: , .
  • Some digraphs are also used:

    The letter i is placed after a vowel letter to indicate that the following consonant was palatalised: ai, ei, oi, ui; ái, éi, ói, úi The letter h is placed after c, t, p to indicate a fricative: ch, th, ph The diphthongs are also indicated by digraphs: áe/, ía, , áu, óe/, úa, éu, óu, iu, au, eu

    The following table indicates the broad pronunciation of various consonant letters in various environments:


  • A dash (—) in an entry indicates that the respective consonant sound is spelled differently under the respective mutation (lenition or nasalisation) and so the indicated consonant letter does not occur then (the spelling c does not occur in a leniting environment; instead, ch /x/ does). See the next two entries.
  • Lenited c, p, t are spelled ch /x/, ph /f/, th /θ/ respectively.
  • Nasalized b, d, g are spelled m-b /mb/, n-d /nd/, n-g /nɡ/ [ŋɡ] respectively.
  • In some cases, lenited f and s are spelled with a superdot.
  • When initial s stemmed from Primitive Irish *sw-, its lenited version is f (written and pronounced).
  • The slender (palatalised) variants of the above consonants occur in the following environments:

  • before a written e, é, i, í;
  • after a written i, when not followed by a vowel letter (but not after the diphthongs , , ).
  • Although Old Irish has both a sound /h/ and a letter h, there is no consistent relationship between the two. Vowel-initial words are sometimes written with an unpronounced h, especially if they are very short (the preposition i "in" was sometimes written hi) or if they need to be emphasised (the name of Ireland, Ériu, was sometimes written Hériu). On the other hand, words that begin with the sound /h/ are usually written without it: a ór /a hoːr/ "her gold". If the sound and the spelling co-occur, it is by coincidence, as ní hed /Nʲiː heð/ "it is not".

    After a vowel or l, n, or r the letters c, p, t can stand for either voiced or voiceless stops; they can also be written double with either value:

    Geminate consonants appear to have existed at the beginning of the Old Irish period but were simplified by the end, as is generally reflected by the spelling generally although double ll, mm, nn, rr were eventually repurposed to indicate nonlenited variants of those sounds in certain positions.

    After a vowel the letters b, d, g stand for the fricatives /v, ð, ɣ/ or their slender equivalents:

    After m, b is a stop, but after d, l and r, it is a fricative:

    After n and r, d is a stop:

    After n, l, and r, g is usually a stop, but it is a fricative in a few words:

    After vowels m is usually a fricative, but sometimes a (nasal) stop, in which case it is also often written double:

    The digraphs ch, ph, th do not occur in word-initial position except under lenition, but wherever they occur, they are pronounced /x/, /f/, /θ/.

    The letters l, n, and r are generally written double when they indicate the tense sonorants, single when they indicate the lax sonorants. Originally, it reflected an actual difference between single and geminate consonants, as tense sonorants in many positions (such as between vowels or word-finally) developed from geminates. As the gemination was lost, the use of written double consonants was repurposed to indicate tense sonorants. Doubly written consonants of this sort do not occur in positions where tense sonorants developed from non-geminated Proto-Celtic sonorants (such as word-initially or before a consonant).

    Written vowels a, ai, e, i in poststressed syllables (except absolutely word-finally) all seem to represent phonemic /ǝ/. The particular vowel that appears is determined by the quality (broad vs. slender) of the surrounding consonants and has no relation to the etymological vowel quality:

    It seems likely that spelling variations reflected allophonic variations in the pronunciation of /ǝ/.


    Old Irish was affected by a series of phonological changes that radically altered its appearance compared with Proto-Celtic and older Celtic languages (such as Gaulish, which still had the appearance of typical early Indo-European languages such as Latin or Ancient Greek). The changes were such that Irish was not recognized as Indo-European at all for much of the 19th century. The changes must have happened quite rapidly, perhaps in only one or two hundred years around 500–600, because almost none of the changes are visible in Primitive Irish (4th to 6th centuries), and all of them are already complete in archaic Old Irish (8th century). A capsule summary of the most important changes is (in approximate order):

    1. Syllable-final *n (from PIE *m, *n) assimilated to the following phoneme, even across word boundaries in the case of syntactically connected words.
    2. Voiceless stops became voiced: *mp *nt *nk > /b d ɡ/.
    3. Voiced stops became prenasalised /ᵐb, ⁿd, ᵑɡ/. They were reduced to simple nasals during the Old Irish period.
    4. Before a vowel, /n-/ was attached to the beginning of the syllable.
    5. Lenition of all single consonants between vowels. That applied across word boundaries in the case of syntactically connected words.
    6. Stops became fricatives.
    7. *s became /h/ (later lost unless the following syllable was stressed).
    8. *w was eventually lost (much later).
    9. *m became a nasalised continuant (/w̃/; perhaps [w̃] or [β̃]).
    10. *l *n *r remained, but the non-lenited variants were strengthened to /L N R/ (see phonology section above).
    11. Extensive umlaut ("affection") of short vowels, which were raised or lowered to agree with the height of following Proto-Celtic vowels. Similarly, rounding of *a to /o/ or /u/ often occurred adjacent to labial consonants.
    12. Palatalization of all consonants before front vowels.
    13. Loss of part or all of final syllables.
    14. Loss of most interior vowels (syncope).

    They led to the following effects:

  • Both the palatalised ("slender") and lenited variants of consonants were phonemicised, multiplying the consonant inventory by four (broad, broad lenited, slender, slender lenited). Variations between broad and slender became an important part of the grammar:
  • in masc. o-stems: macc "son" (nom. acc.) vs. maicc (gen.), cúl "back" (nom. acc.) vs. cúil (gen.), cf. Latin -us (nom.), -um (acc.) vs. (gen.);
  • in fem. ā-stems: túath "tribe, people" (nom.) vs. túaith (acc. dat.), mucc "pig" (nom.) vs. muicc (acc. dat.);
  • in r-stems: athar "father" (gen.) vs. ath(a)ir (nom. acc. dat.).
  • Lenition and nasal assimilation across word boundaries in syntactically connected words produced extensive sandhi effects (Irish initial mutations). The variations became an important part of the grammar.
  • Both umlaut (vowel affection) and especially syncope radically increased the amount of allomorphy found across declensions and conjugations. The most dramatic deviations are due to syncope: compare as·berat "they say" vs. ní-epret "they do not say" or do·sc(a)i "he surpasses" vs. ní-derscaigi "he does not surpass" (where the stressed syllable is boldfaced).
  • Examples of changes

    The following are some examples of changes between Primitive Irish and Old Irish.


    These various changes, especially syncope, produced quite complex allomorphy, because the addition of prefixes or various pre-verbal particles (proclitics) in Proto-Celtic changed the syllable containing the stress: According to the Celtic variant of Wackernagel's Law, the stress fell on the second syllable of the verbal complex, including any prefixes and clitics. By the Old Irish period, most of this allomorphy still remained, although it was rapidly eliminated beginning in the Middle Irish period.

    Among the most striking changes are in prefixed verbs with or without pre-verbal particles. With a single prefix and without a proclitic, stress falls on the verbal root, which assumes the deuterotonic ("second-stressed") form. With a prefix and also with a proclitic, stress falls on the prefix, and the verb assumes the prototonic ("first-stressed") form. Rather extreme allomorphic differences can result:

    The following table shows how these forms might have been derived:

    The most extreme allomorphy of all came from the third person singular of the s-subjunctive because an athematic person marker -t was used, added directly onto the verbal stem (formed by adding -s directly onto the root). That led to a complex word-final cluster, which was deleted entirely. In the prototonic form (after two proclitics), the root was unstressed and thus the root vowel was also deleted, leaving only the first consonant:

    Syncope in detail

    In more detail, syncope of final and intervocalic syllables involved the following steps (in approximate order):

  • Shortening of absolutely final long vowels.
  • Loss of most final consonants, including *m, *n, *d, *t, *k, and all clusters involving *s (except *rs, *ls, where only the *s is lost).
  • Loss of absolutely final short vowels (including those that became final as a result of loss of a final consonant and original long final vowels).
  • Shortening of long vowels in unstressed syllables.
  • Collapsing of vowels in hiatus (producing new unstressed long vowels).
  • Syncope (deletion) of vowels in every other interior unstressed syllable following the stress. If there are two remaining syllables after the stress, the first one loses its vowel; if there are four remaining syllables after the stress, the first and third lose their vowel.
  • Resolution of impossible clusters resulting from syncope and final-vowel deletion:
  • Adjacent homorganic obstruents where either sound was a fricative became a geminate stop, voiceless if either sound was voiceless (e.g. *ðð *dð *ðd > /dd/; *θð *ðθ *θd *tθ etc. > /tt/).
  • Otherwise, adjacent obstruents assumed the voicing of the second consonant (e.g. *dt > /tt/; *kd > /gd/; *ɣt > /xt/).
  • *l *r *n not adjacent to a vowel became syllabic and then had a vowel inserted before them (e.g. domun "world" < *domn < *domnos < *dumnos; immormus "sin" < *imm-ro-mess). However, in the case of *n, that occurred only when the nasal had not previously been joined to a following voiced stop as a result of nasal assimilation: compare frecnd(a)irc "present" (disyllabic).
  • Remaining impossible clusters were generally simplified by deletion of consonants not adjacent to vowels (such as between other consonants). However, Old Irish tolerated geminates adjacent to other consonants as well other quite complex clusters: ainm /aNʲm/ "name" (one syllable), fedb /fʲeðβ/ "widow", do-aidbdetar /do-ˈaðʲβʲðʲǝdǝr/ "they are shown".
  • Proto-Celtic short vowels, vowel affection

    All five Proto-Celtic short vowels (*a, *e, *i, *o, *u) survived into Primitive Irish more or less unchanged in stressed syllables.

    However, during the runup to Old Irish, several mutations (umlauts) take place. Former vowels are modified in various ways depending on the following vowels (or sometimes surrounding consonants). The mutations are known in Celtic literature as affections or infections such as these, the most important ones:

    1. i-affection: Short *e and *o are raised to i and u when the following syllable contains a high vowel (*i, , *u, ). It does not happen when the vowels are separated by certain consonant groups.
    2. a-affection: Short *i and *u are lowered to e and o when the following syllable contains a non-high back vowel (*a, , *o, ).
    3. u-affection: Short *a, *e, *i are broken to short diphthongs au, eu, iu when the following syllable contains a *u or that was later lost. It is assumed that at the point the change operated, u-vowels that were later lost were short *u while those that remain were long . The change operates after i-affection so original *e may end up as iu.

    Nominal examples (reconstructed forms are Primitive Irish unless otherwise indicated):

  • sen "old (nominative singular)" < *senos, but sin "old (genitive singular)" < *senī (i-affection), siun "old (dative singular)" < *senu (i-affection and u-affection) < *senū < PIE *senōi, sinu "old (accusative plural)" < *senūs (i-affection but no u-affection because u remains) < PIE *senons.
  • fer "man (nominative singular)" < *wiros (a-affection), but fir "man (genitive singular)" < *wirī (no a-affection), fiur "man (dative singular)" < *wiru (u-affection) < *wirū < PIE *wirōi, firu "men (accusative plural)" < *wirūs (no u-affection because the u remains) < PIE *wirons.
  • nert "strength (nominative singular)", but neurt "strength (dative singular)" < *nertu (u-affection but no i-affection, which was blocked by the cluster rt) < *nertū < PIE *nertōi.
  • mil "honey" (i-affection) < PCelt *meli, milis "sweet" < *melissos (i-affection).
  • fiurt "miracle (nominative singular)" < *wirtus (u-affection; from Latin virtus), fert(a)e "miracle (nominative plural)" < *wirtowes.
  • Verbal paradigm example:

    The result of i-affection and a-affection is that it is often impossible to distinguish whether the root vowel was originally *e or *i (sen < *senos and fer < *wiros have identical declensions). However, note the cases of nert vs. fiurt above for which i-affection, but not a-affection, was blocked by an intervening rt.

    Proto-Celtic long vowels and diphthongs

    Proto-Celtic long vowels and diphthongs develop in stressed syllables as follows:

    The Old Irish diphthongs úi, éu, íu stem from earlier sequences of short vowels separated by *w, e.g. drúid- "druid" < *dru-wid- "tree-knower".

    Most instances of é and ó in nonarchaic Old Irish are due to compensatory lengthening of short vowels before lost consonants or to the merging of two short vowels in hiatus: cét /kʲeːd/ ‘hundred’ < Proto-Celtic kantom (cf. Welsh cant) < PIE *kṃtóm.


    See Proto-Celtic for various changes that occurred in all the Celtic languages, but these are the most important:

  • PIE *gʷ > Proto-Celtic *b (but PIE *gʷʰ > *gʷ).
  • Loss of aspiration in *bʰ *dʰ *gʰ *gʷʰ.
  • Loss of *p. Initially and intervocalically it was simply deleted; elsewhere, it variously became *w, *b, *x etc.
  • From Proto-Celtic to Old Irish, the most important changes are these:

  • Lenition and palatalisation, multiplying the entire set of consonants by 4. See #History for more details.
  • Loss of most final consonants. See #Syncope in detail.
  • Proto-Celtic *s is lenited to /h/, which then disappears between vowels. In general, Old Irish s when not word-initial stems from earlier geminate ss (often still written as such, especially in archaic sources).
  • Proto-Celtic *kʷ *gʷ remain in Ogam Irish (maqqi "son" (gen. sg.)) but become simple c g in Old Irish. Occasionally, they leave their mark by rounding the following vowel.
  • Proto-Celtic *w is lost early on between vowels, followed by early hiatus resolution. In some cases, *w combines with a preceding vowel to form a diphthong: béu béo "living, alive" < *bewas < *biwos < *gʷiwos. Other instances of *w become [β], which still remains in Ogam Irish. By Old Irish times, this becomes f- initially (e.g. fer "man" < *wiros, flaith "lordship" < *wlātis), lenited b after lenited voiced sounds (e.g. tarb "bull" < *tarwos, fedb "widow" < *widwā), f after lenited *s (lenited fïur "sister" < *swesōr), and is lost otherwise (e.g. dáu "two" < *dwōu, unlenited sïur "sister" < *swesōr).
  • Proto-Celtic *y becomes *iy after a consonant, much as in Latin. The vowel *i often survives before a lost final vowel, partly indicating the nature of the final vowel as a result of vowel affection: cride cridi cridiu "heart" (nom. gen. dat.) < *krideon *kridiī *kridiū < *kridiyom *kridiyī *kridiyū < Post-PIE *kṛdyom *kṛdyī *kṛdyōi. After this, *y is lost everywhere (after palatalising a preceding consonant).
  • Initial clusters

    Old Irish preserves, intact, most initial clusters unlike many other Indo-European languages.

    Preserved initial clusters:

  • sn- smr- sr- sl- sc- scr- scl-, e.g. snám "swimming", smiur "marrow", sruth "stream", scáth "shadow, reflection", scrissid "he scratches (out)", scléo "misery (?)".
  • cr- cl- cn-, e.g. crú "blood", cloth "fame", cnú "nut".
  • gr- gl- gn-, e.g. grían "sun", glé "clear", gnáth "customary".
  • tr- tl- tn-, e.g. tromm "heavy', tlacht "garment", tnúth "jealousy, passion".
  • dr- dl-, e.g. dringid "he climbs", dlong(a)id "he cleaves".
  • mr- ml-, e.g. mruig "land", mliuchtae "milch".
  • br- bl-, e.g. brú "belly", bláth "flower".
  • Modified initial clusters:

  • *wl- *wr- > fl- fr-, e.g. flaith "lordship" < *wlātis, froích "heather" < *wroikos.
  • *sp-/*sw- > s- (lenited f-), e.g. sïur "sister" (lenited fïur) < *suior < PIE *swesōr.
  • *st- > t-, e.g. tíagu "I go" < *stēgū-s < post-IE *steigʰō.
  • *pl- *pr- lose the *p.
  • PIE *gʷn- > Proto-Celtic *bn- > mn-, e.g. mná "woman" (gen. sg.) < *bnās < PIE *gʷneh₂s, an extremely archaic noun form.
  • Intervocalic clusters

    Many intervocalic clusters are reduced, becoming either a geminate consonant or a simple consonant with compensatory lengthening of the previous vowel. During the Old Irish period, geminates are reduced to simple consonants, occurring earliest when adjacent to a consonant. By the end of the Old Irish period, written ll mm nn rr are repurposed to indicate the non-lenited sounds /L m N R/ when occurring after a vowel and not before a consonant.

    Cluster reduction involving *n:

  • *nt *nk > unlenited /d g/ (normally written t c). Note that PCelt *ant,*ent > *ent > /eːd/ but *int *ont *unt > /idd odd udd/ like *nk: cét /kʲeːd/ "hundred" < PCelt *kantom (cf. Welsh cant) < PIE *kṃtóm; sét /sʲeːd/ "way" < *sentu- (vs. Breton hent); ro·icc, ric(c) /r(o)-iɡɡ/ "he reaches" < *ro-ink- (vs. Bret rankout "must, owe"); tocad /toɡað/ "luck" (vs. Bret tonkad "fate").
  • *ns > unlenited s with compensatory lengthening of a preceding vowel; *ans > *ens > és similarly to *ant *ank: géis "swan" < PCelt *gansi- < PIE *ǵʰh₂ens- (vs. Dutch gans "goose").
  • Cluster reduction involving *s *z:

  • Medial *sm *sn *sl > mm nn ll: am(m) "I am" < PIE *esmi.
  • Medially, *st > ss (but *str > str, *rst > rt).
  • *zb > db /ðv/, *zg > dg /ðɣ/ (but rg after an unstressed syllable), *zd > /dd/: net /nedd/ "nest" < PIE *nisdos /nizdos/.
  • Lenited stops *x generally disappear before sonorants *r *l *n *m, with compensatory lengthening of the preceding vowel. Many examples occur in reduplicated preterites or words with consonant-final prefixes (such as ad-):

  • du·air-chér "I have purchased" < *-xexr < PCelt *-kikra;
  • ·cúal(a)e "he heard" < *koxlowe < PCelt *kuklowe;
  • áram "number" < *að-rīm;
  • ám thám "a moving to and fro" < *aɣm θ-aɣm (verbal nouns of agid "he drives" and compound do·aig);
  • dál "assembly" < *daθl (cf. Old Welsh datl).
  • However, *θr, *βr, *βl survive: críathraid "he perforates" < PCelt *krētrāti-s; gabur "goat" < PCelt *gabros (cf. Welsh gafr); mebul "shame" (cf. Welsh mefl).


    Old Irish Wikipedia