Old Irish

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Old Irish
Pronunciation [ˈɡoːi̯ðʲelɡ]
Region Ireland, Isle of Man, western coast of Great Britain
Era 6th century–10th century; evolved into Middle Irish about the 10th century
Early forms
Primitive Irish
  • Old Irish
Language codes
ISO 639-2 sga
ISO 639-3 sga
Glottolog oldi1245[1]
Linguasphere 50-AAD-ad
This article contains IPA phonetic symbols. Without proper rendering support, you may see question marks, boxes, or other symbols instead of Unicode characters.

Old Irish (Old Irish: Goídelc) (sometimes called Old Gaelic[2][3]) is the name given to the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from c. AD 600–900. The primary contemporary texts are dated c. AD 700–850; by AD 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.[2]

Old Irish is known for having a particularly complex system of morphology and especially of allomorphy (i.e. 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 which the now extinct Cornish language also featured. Because these languages belong to the Brittonic branch of the Celtic language group (so-called "P-Celtic"), initial mutation must pre-date the split in the development paths of the Brittonic and Goidelic languages. No mutations are however attested in Gaulish material, therefore a parallel evolution of this 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, among them Rudolf Thurneysen (1857–1940) and Osborn Bergin (1873–1950).

Notable characteristics

The complex systems of allomorphy and consonant mutations – probably the two most salient characteristics of Old Irish compared with other old Indo-European languages — have been mentioned above. Other notable characteristics are:

  • A system of conjugated prepositions that is unusual in Indo-European languages (although found in many Semitic languages, e.g. Arabic), e.g. 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 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 (e.g. o-, yo-, ā-, -, i-, u-, r-, n-, s-, and consonant stems). Most of the complexities of PIE verbal conjugation are also maintained, in addition to new complexities introduced by various sound changes (see below).

Consonant mutations

In the system of initial consonant mutations, the initial consonant of a word must be modified in one or another way, depending on the nature of the preceding word. An example is "la teg" /la tʲeɣ/ "towards a house" vs. "fo theg" /fo θʲeɣ/ "under a house" "i teg" /i dʲeɣ/ "into a house", with the alternation /t ~ θ ~ d/ in the initial consonant of "teg" "house" triggered by the preceding preposition.

There are four types of mutation:

  • no change
  • "lenition" (softening, producing /b ~ v/, /t ~ θ/, /f ~ ∅/, etc.)
  • "nasalisation" (producing /b ~ mb/, /t ~ d/, etc.)
  • "aspiration" (only visible between two vowels, where an /h/ appears, e.g. "a ech" /a hex/ "her horse")

In general there is no way to predict from the form of a given word which type of mutation it will trigger. (Note that the spelling of the initial consonant does not always change to indicate mutation in Old Irish, although it generally does starting in Middle Irish).

In many cases the mutation has grammatical significance; an example is "a teg" /a tʲeɣ/ "her house" vs. "a theg" /a θʲeɣ/ "his house" vs. "a teg" /a dʲeɣ/ "their house", where the mutation is the only thing distinguishing the three meanings "her" vs. "his" vs. "their" of the possessive pronoun "a".

Mutations can also signal various other grammatical features, e.g. noun case in "fer becc" /fʲer bʲeɡ/ "small man (nom. sg.)" vs. "fer m-becc" /fʲer mbʲeɡ/ "small man (acc. sg.)" vs. "dá fer becc" /daː er vʲeɡ/ "two small men (nom.)", in this case with an alternation /b ~ v ~ mb/ signalling the different cases of the otherwise identical form "fer" (but note that "dá" "two" also mutates the following word, in this case causing the loss of /f/ in "fer"). Another grammatical feature signalled by mutations is relative clause attachment, where lenition indicates the beginning of a relative clause, often in place of any explicit relative pronoun (although in some cases the verbal ending also changes to a special relative form).

Verbal allomorphy

The system of Old Irish allomorphy, particularly in verbal conjugation, is notoriously complex and unpredictable, even among the already highly complex verbal morphology of other old Indo-European languages (e.g. Sanskrit, Ancient Greek, Latin). Not only does Old Irish preserve most aspects of the already quite complex Proto-Indo-European (PIE) verbal system, but adds major new complexities due the interaction of a series of sound changes with shifting stress positions.

Verbs are conjugated in three persons, two numbers (singular, plural), three voices (active, passive, deponent)[clarification needed], three moods (indicative, subjunctive, imperative), and four tenses (present, future, past imperfective, past perfective preterite) - and three aspects, aorist, perfective and imperfective. Most of the complexities of PIE verbal conjugation are still present: primary and secondary endings; thematic and athematic endings; active and deponent (originally mediopassive) endings, as well as innovative passive endings; multiple verb stems for each verb, which must be memorised as principal parts; and numerous means of verb-stem formation (reduplication, ablaut, n-infixing, various stem suffixes, etc.).

On top of this, however, there are different conjugations used when no vs. one prefix precedes (termed absolute vs. conjunct, respectively), e.g. biru "I carry", berid "he carries" vs. ní-biur "I do not carry", ní-beir "he does not carry" (with negative prefix ní-) or do⋅biur "I bring/give", do⋅beir "he brings/gives" (with verbal prefix do- "to"). (As shown in these examples, there is significant umlaut vowel variation in verbal paradigms, triggered by lost vowels; this operates in addition to the inherited system of Indo-European ablaut vowel variation.)

When two or more prefixes precede it gets even more complex, with a special conjunct prototonic conjugation required, e.g. ní-tabur "I do not bring/give", ní-tabair "he does not bring/give". In such cases, the stem merges with all but the first prefix in a complex and often unpredictable fashion, e.g. do⋅berat "they bring/give" vs. ní-taibret "they do not bring/give" but as⋅berat "they say" (with verbal prefix as- "out of") vs. ní-epret "they do not say".

In the s-subjunctive, the allormorphy is even more extreme, especially in the third-person singular: cf. indicative as⋅boind "he refuses" vs. ní⋅opaind "he does not refuse", subjunctive as⋅bó "he may refuse" vs. ní⋅op "he may not refuse". In many cases, from a synchronic perspective, the changes appear utterly random (e.g. do⋅rósc(a)i "he surpasses" vs. ní-derscaigi "he does not surpass") or even unrecognisable (e.g. imm⋅soí "he turns around" vs. ní-impaí "he does not turn around"). However, these forms mostly result from a series of regular sound changes (see below).[* 1]


Old Irish was the only member of the Goidelic/Gaelic branch of the Celtic languages, which is in turn a sub-family of the wider Indo-European language family that also includes the Slavonic, Italic/Romance, Indo-Aryan and Germanic sub-families, along with several others. Old Irish is the ancestor of all the 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. These inscriptions date from about the 4th to the 6th centuries. Primitive Irish appears to be very close to Common Celtic, the ancestor of all Celtic languages, and has a lot of the characteristics of other archaic Indo-European languages.


Relatively little survives in the way of strictly contemporary sources. These are mainly represented by shorter or longer glosses on the margins or between the lines of religious Latin manuscripts, most of them preserved in monasteries in Germany, Italy, Switzerland, France and Austria, having been taken there by early Irish missionaries. Whereas in Ireland, many of the older manuscripts appear to have been worn out through extended and heavy use, their counterparts on the Continent were much less prone to the same risk, because once they ceased to be understood, they were rarely consulted.[4]

The earliest Old Irish passages may be the transcripts found in the Cambrai Homily, which is thought to belong to the early 8th century. The Book of Armagh contains texts from the early 9th century. Important Continental collections of glosses from the 8th and 9th century include the Würzburg Glosses (mainly) on the Pauline Epistles, the Milan Glosses on a commentary to the Psalms and the St Gall Glosses on Priscian's Grammar. Further examples are found at Karlsruhe (Germany), Paris (France), Milan, Florence and Turin (Italy). A late 9th-century manuscript from the abbey at Reichenau, now in St. Paul in Carinthia (Austria), contains a spell and four Old Irish poems. The Liber Hymnorum and the Stowe Missal date from about 900 to 1050.

In addition to contemporary witnesses, the vast majority of Old Irish texts are attested in manuscripts of a variety of later dates. Manuscripts of the later Middle Irish period, for instance, such as the Lebor na hUidre and the Book of Leinster, contain texts which are thought to derive from written exemplars in Old Irish now lost and retain enough of their original form to merit classification as Old Irish. The preservation of certain linguistic forms which were current in the Old Irish period may provide reason to assume that an Old Irish original directly or indirectly underlies the transmitted text or texts.



The consonant inventory of Old Irish is shown in the chart below. The complexity of Old Irish phonology is due to a four-way split of phonemes inherited from Primitive Irish, with both a fortis–lenis and a "broad–slender" (velarised vs. palatalised) distinction arising due to 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/.)

  Labial Dental Alveolar Velar Glottal
Nasal broad m N  n ŋ  
slender Nʲ  nʲ ŋʲ  
Plosive broad p  b t  d k  ɡ  
slender pʲ  bʲ tʲ  dʲ kʲ  ɡʲ  
Fricative broad f  v θ  ð s x  ɣ h
slender fʲ  vʲ θʲ  ðʲ xʲ  ɣʲ
slender ṽʲ        
Approximant broad   R  r    
slender   Rʲ  rʲ    
Lateral broad   L  l    
slender   Lʲ  lʲ    

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/ and/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 (e.g. 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.


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, same as long vowels. (This is much like the situation in Old English, but different from e.g. Ancient Greek, whose shorter and longer diphthongs were bimoraic and trimoraic, respectively, e.g. /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:

  Monophthongs Diphthongs
Close i u ĭu
Mid e o ĕu (ŏu)1
Open a ău

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

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

  Monophthongs Diphthongs
Close iu ui
Mid e₁ː, e₂ː1 o₁ː, (o₂ː?)2 eu oi, (ou)3
Open ai, au3

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 due to 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/.[5] Perhaps /e₁ː/ was [eː] while /e₂ː/ was [ɛː]. They are clearly distinguished in later Old Irish, where /e₁ː/ becomes ía (but é before a palatal consonant), while /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/ only existed in early archaic Old Irish (c. AD 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). This late ó does not develop into úa, suggesting that áu > ó post-dated ó > úa.

Later Old Irish had the following inventory of long vowels:

  Monophthongs Diphthongs
Close iu, ia ui, ua
Mid eu oi?1

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:

Old Irish Pronunciation English Annotations
marba /ˈmarva/ kill 1

sg. subj.

léicea /ˈLʲeːɡʲa/ leave 1

sg. subj.

marbae /ˈmarve/ ([ˈmarvɘ]?) kill 2

sg. subj.

léice /ˈLʲeːɡʲe/ leave 2

sg. subj.

marbai /ˈmarvi/ ([ˈmarvɨ]?) kill 2

sg. indic.

léici /ˈlʲeːɡʲi/ leave 2

sg. indic.

súlo /ˈsuːlo/ eye gen.
doirseo /ˈdoRʲsʲo/ door gen.
marbu /ˈmarvu/ kill 1

sg. indic.

léiciu /ˈLʲeːɡʲu/ leave 1

sg. indic.

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 do not in general 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 (e.g. cenél "kindred, gender" < *cenethl; du⋅air-chér "I have purchased" < *-chechr, preterite of crenaid "buys"[6]);
  • 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 (cf. erríndem "highest" vs. rind "peak"[7]).


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 (e.g. the verbal prefix as- in as⋅beir /asˈberʲ/ "he says"). In such cases, the unstressed prefix is indicated in grammatical works with a following center 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: , .

A number of digraphs are also used:

The letter i is placed after a vowel letter to indicate that the following consonant was slender: 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:

Consonant letter Word-initial After a vowel
unmutated nasalised lenited
b /b/ /v/
c /k/ /ɡ/ /k, ɡ/
d /d/ /ð/
f /f/ /v/ silent /f/
g /ɡ/ /ɣ/
h See discussion below
l /L/ /l/
m /m/ /ṽ/
n /N/ /n/
p /p/ /b/ /p, b/
r /R/ /r/
s /s/ /h/ /s/
t /t/ /d/ /t, d/


  • A dash (—) in an entry indicates that the respective consonant sound is spelled differently under the respective mutation (lenition or nasalisation) and hence the indicated consonant letter does not occur in this situation (e.g. 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, for example 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:

Old Irish Pronunciation English
mac or macc /mak(k)/ son
bec or becc /bʲeɡ(ɡ)/ small
op or opp /ob(b)/ refuse
brat or bratt /brat(t)/ mantle
brot or brott /brod(d)/ goad
derc /dʲerk/ hole
derc /dʲerɡ/ red
daltae /daLte/ fosterling
celtae /kʲeLde/ who hide
anta /aNta/ of remaining
antae /aNde/ who remain

Geminate consonants appear to have existed at the beginning of the Old Irish period, but were simplified by the end, and the spelling generally reflects this, although double ll mm nn rr were eventually repurposed to indicate non-lenited variants of these sounds in certain positions.

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

Old Irish Pronunciation English
dub /duv/ black
mod /moð/ work
mug /muɣ/ slave
claideb /klaðʲǝv/ sword
claidib /klaðʲǝvʲ/ swords

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

Old Irish Pronunciation English
imb /imʲbʲ/ butter
odb /oðv/ knot (in a tree)
delb /dʲelv/ image
marb /marv/ dead

After n and r, d is a stop:

Old Irish Pronunciation English
bind /bʲiNʲdʲ/ melodious
cerd /kʲeRd/ "art, skill"

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

Old Irish Pronunciation English
long /Loŋɡ/ ship
delg or delc /dʲelɡ/ thorn
argat or arggat /arɡ(ɡ)ǝd/ silver
ingen[* 2] /inʲɣʲǝn/ daughter
ingen[* 2] /iNʲɡʲǝn/ nail, claw
bairgen /barʲɣʲǝn/ loaf of bread

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

Old Irish Pronunciation English
dám /daːṽ/ company
lom or lomm /Lom/ bare

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/.

Old Irish Pronunciation English
ech /ex/ horse
oíph /oif/ beauty
áth /aːθ/ ford

The letters l, n, and r are generally written double when they indicate the tense sonorants, single when they indicate the lax sonorants. Originally this reflected an actual difference between single and geminate consonants, as tense sonorants in many positions (e.g. between vowels or word-finally) developed from geminates. But 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 (e.g. word-initially or before a consonant).

Old Irish Pronunciation English
corr /koR/ crane
cor /kor/ putting
coll /koL/ hazel
col /kol/ sin
sonn /soN/ stake
son /son/ sound
ingen[* 2] /inʲɣʲǝn/ daughter
ingen[* 2] /iNʲɡʲǝn/ nail, claw

Written vowels a, ai, e, i in post-stressed 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:

Preceding consonant Following consonant Spelling Example
broad broad a dígal /ˈdʲiːɣǝl/ "vengeance" (nom.)
broad slender (in open syllable) a
broad slender (in closed syllable) ai dígail /ˈdʲiːɣǝlʲ/ "vengeance" (acc./dat.)
slender broad e dliged /ˈdʲlʲiɣʲǝð/ "law" (acc.)
slender slender i dligid /ˈdʲlʲiɣʲǝðʲ/ "law" (gen.)

It seems likely that the 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 (e.g. Gaulish, which still had the appearance of typical early Indo-European languages such as Latin or Ancient Greek). These changes were such that Irish was not recognized as Indo-European at all during much of the 19th century. The changes must have happened quite rapidly, perhaps in a one or two-century period c. AD 500–600, because almost none of the changes are visible in Primitive Irish (4th to 6th centuries AD) and all of them are already complete in archaic Old Irish (8th century AD). A capsule summary of the most important changes is (in approximate order):[8][9]

  1. Syllable-final *n (from PIE *m, *n) assimilated to the following phoneme, include across word boundaries in the case of syntactically connected words.
    • Voiceless stops became voiced: *mp *nt *nk > /b d ɡ/.
    • Voiced stops became prenasalised /mb nd ŋɡ/. These were reduced to simple nasals during the Old Irish period.
    • Before a vowel, /n-/ was attached to the beginning of the syllable.
  2. Lenition of all single consonants between vowels. This applied across word boundaries in the case of syntactically connected words.
    • Stops became fricatives.
    • *s became /h/ (later lost unless the following syllable was stressed).
    • *w was eventually lost (much later).
    • *m became a nasalised continuant (/w̃/; perhaps [w̃] or [β̃]).
    • *l *n *r remained, but the non-lenited variants were strengthened to /L N R/ (see phonology section above).
  3. 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.
  4. Palatalization of all consonants before front vowels.
  5. Loss of part or all of final syllables.
  6. Loss of most interior vowels (syncope).

These led to the following effects:

  • Both the palatalised ("slender") and lenited variants of consonants were phonemicised, multiplying the consonant inventory by 4 (broad, broad lenited, slender, slender lenited). *Variations between broad and slender became an important part of the grammar. e.g.:
    • 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). These 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: cf. 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.

Primitive Irish Old Irish Meaning
inigena[10] ingen daughter
qrimitir[11] cruimther priest
maqqi[12] maicc son (gen.)
velitas[13] filed poet (gen.)
Lugudeccas[14] Luigdech genitive of Lug(u)id (name)
Anavlamattias[15] Anfolmithe genitive of Anblamath (name)
Coillabotas[16] Coílbad genitive of name

Initial mutations

All words within a syntactic phrase were treated phonologically as a single unit for the purpose of lenition and nasal assimilation, producing extensive sandhi effects. Synchronically these were unpredictable, but diachronically they reflected the state of the original final syllable in Primitive Irish:

  • Lenition: If the word originally ended in a vowel, the first consonant of the following word was lenited.
  • Gemination: If the syllable originally ended in *-s, or in *-t or *-k after a vowel, the first consonant was geminated, while /h-/ appeared before a vowel-initial word (regularly from *-s, analogically in the other cases). By Old Irish times, this gemination appeared only after vowel-final words.
  • Nasalization (eclipsis): If the syllable originally ended in a nasal, the nasal is attached to the beginning of the following word, with various further changes (see above).

These mutations became an important part of the grammar, and remain with little change in modern Irish (see Irish initial mutations).

Mutations were only partly noted in Old Irish spelling:

  • Lenition is only clearly indicated in the case of initial voiceless stops (written ph th ch) and (in later Old Irish) initial /f- s-/ (written ḟ ṡ).
  • Nasalization is only clearly indicated in the case of initial voiced stops and vowels, where n- is prefixed (m- before b).
  • Gemination is only partly indicated when geminated consonants were produced (geminated consonants were in the process of reducing to single consonants in Old Irish times). It was not indicated at all when /h-/ resulted.

The fact that mutations applied more extensively than indicated in spelling is largely inferred from later written and modern spoken evidence.


forms of fer becc "small man", fer cumachtach "powerful man"
Singular Plural
Old Irish Prim Irish ending Old Irish Prim Irish ending
Nom fer becc /fʲer bʲegg/, fer cumachtach /k-/ *-os fir bicc /fʲirʲ vʲigʲgʲ/, fir chumach(a)ig /x-/ *-ī < PIE *-oi
Voc fir bicc /fʲirʲ vʲigʲgʲ/, fir chumach(a)ig /x-/ *-e firu biccu /fʲiru bʲiggu/, firu cumachtchu /k-/ *-ūs < PIE *-ōs
Acc fer m-becc /fʲer mbʲegg/, fer cumachtach /g-/ *-on < PIE *-om firu biccu /fʲiru bʲiggu/, firu cumachtchu /k-/ *-ūs < PIE *-ōns
Gen fir bicc /fʲirʲ vʲigʲgʲ/, fir chumach(a)ig /x-/ *-ī fer m-becc /fʲer mbʲegg/, fer cumachtach /g-/ *-on < PIE *-ōm
Dat fiur biucc /fʲĭŭr vʲĭŭgg/, fiur chumachtach /x-/ *-ū < *-ūi < PIE *-ōi fer(a)ib becc(a)ib /fʲerǝvʲ bʲeggǝvʲ/, fer(a)ib cumachtch(a)ib /k-/ -obis < PIE *-obhis

In the case of a "his, her, its, their", only the initial mutation of the following word distinguishes the various meanings.

initial mutation after a "his, her, its, their"
Effect ech "horse" bo "cow" teg "house" PIE form[17] Sanskrit form
Masc/Neut Sing Lenition a ech /a ex/ a bo /a vo/ a theg /a θʲeɣ/ *esyo[* 3] asya
Fem Sing Gemination a ech /a hex/ a bo /a bbo/ a teg /a ttʲeɣ/ *esyās < *esyeh₂s asyās
Plur Nasalization a n-ech /a nex/ a m-bo /a mbo/ a teg /a dʲeɣ/ Masc/Neut *eysōm? *eysoHom? *eysom? (*es-?)
Fem *eys-? (*es-?) *ih₂s-?[* 4]
ēṡām (fem. āsām)


These various changes, esp. 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, e.g.:

Example differences between deuterotonic and prototonic forms of various verbs. Stress falls directly after the center dot or hyphen.[18]
Earlier form Deuterotonic Meaning Prototonic Meaning
*ess-bero(n)t < PIE *-bheronti as·berat /as-ˈbʲerəd/ they say ní-epret /Nʲiː-ˈhebrʲəd/ they do not say
*cum-uss-ana con·osna he rests ní-cumsana he does not rest
*de-ro-uss-scochi do·rósc(a)i he surpasses ní-derscaigi he does not surpass
*de-lugi < PIE *-logheyeti do·lug(a)i he pardons ní-dílg(a)i he does not pardon
*de-ro-gn... do·róna he may do ní-derna he may not do

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

Possible derivation of some verbal forms
"they say" "they do not say" "he rests" "he does not rest" "he surpasses" "he does not surpass"
Post-PIE eks bheronti nē eks bheronti kom uks h₂eneh₂ti nē kom uks h₂eneh₂ti dē pro uks skokeyeti nē dē pro uks skokeyeti
Proto-Celtic eks ˈberonti nī ˈeks-beronti kom ˈuks-anāti nī ˈkom-uks-anāti dī ˈro-uks-skokīti nī ˈdī-ro-uks-skokīti
Early Irish ess-es ˈberont ní-s ˈess-beront kon-es ˈuss-anát ní-s ˈkom-uss-anát dí-s ˈro-uss-skokít ní-s ˈdi-ro-uss-skokít
Nasal assimilation ess-es ˈberodd ní-s ˈess-berodd --- --- --- ---
Lenition es-eh ˈberod Ní-h ˈes-berod kon-eh ˈus-anáθ Ní-h ˈkow̃-us-anáθ dí-h ˈRo-us-skoxíθ Ní-h ˈdi-ro-us-skoxíθ
Palatalization es-eh ˈbʲerod Nʲí-h ˈes-bʲerod --- Nʲí-h ˈkow̃-us-anáθ dʲí-h ˈRo-us-skoxʲíθ Nʲí-h ˈdʲi-ro-us-skoxʲíθ
Hiatus reduction --- --- --- --- dʲí-h ˈRós-skoxʲíθ Nʲí-h ˈdʲi-rós-skoxʲíθ
Umlaut (vowel affection) --- --- kon-eh ˈos-anáθ Nʲí-h ˈkuw̃-us-anáθ --- Nʲí-h ˈdʲe-rós-skoxʲíθ
Shortening of absolutely final vowel --- --- --- --- --- ---
Loss/assimilation of final consonant(s) es-e bʲ-ˈbʲerod Nʲí h-ˈes-bʲerod kon-e h-ˈos-aná Nʲí k-ˈkuw̃-us-aná dʲí R-ˈRós-skoxʲí Nʲí d-ˈdʲe-rós-skoxʲí
Mora reduction in unstressed final vowel es bʲ-ˈbʲerod --- kon h-ˈos-ana Nʲí k-ˈkuw̃-us-ana dʲí R-ˈRós-skoxʲi Nʲí d-ˈdʲe-rós-skoxʲi
Consonant assimilation es ˈbʲerod Nʲí h-ˈebʲ-bʲerod kon h-ˈos-ana Nʲí k-ˈkuw̃-us-ana dʲí R-ˈRós-skoxʲi Nʲí d-ˈdʲe-rós-skoxʲi
Syncope es ˈbʲerod Nʲí h-ˈebʲbʲrod kon h-ˈosna Nʲí k-ˈkuw̃sana dʲí R-ˈRósskxʲi Nʲíd-ˈdʲersskoxʲi
Further consonant assimilation --- Nʲí h-ˈebʲbʲrʲod kon ˈosna --- dʲí R-ˈRósski Nʲíd-ˈdʲerskoxʲi
Unstressed vowel reduction es ˈbʲerǝd Nʲí h-ˈebʲbʲrʲǝd --- Nʲí k-ˈkuw̃sǝna di R-ˈRósski Nʲí d-ˈdʲerskǝxʲi
Prepositional modification as ˈbʲerǝd --- --- --- do R-ˈRósski ---
Geminate reduction (non-vocalic-adjacent); sandhi geminate reduction as·ˈbʲerǝd Nʲíh-ˈebrʲǝd kon·ˈosna Nʲí-ˈkuw̃sǝna do·ˈRóski Nʲí-ˈdʲerskǝxʲi
Fricative voicing between unstressed syllables --- --- --- --- --- Nʲíd-ˈdʲerskǝɣʲi
Old Irish pronunciation as·ˈbʲerǝd Nʲí-h-ˈebrʲǝd kon·ˈosna Nʲí-ˈkuw̃sǝna do·ˈRóski Nʲí-ˈdʲerskǝɣʲi
Old Irish spelling as·berat ní-epret con·osna ní-(c)cumsana do·rósc(a)i ní-(d)derscaigi

The most extreme allomorphy of all came from the 3rd 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). This 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. Examples:

Examples of extreme allomorphy of 3rd person singular s-subjunctive, conjunct[19]
Present Indicative Present Subjunctive
Positive (Deuterotonic) Negative (Prototonic) Positive (Deuterotonic) Negative (Prototonic)
Primitive Irish Old Irish Primitive Irish Old Irish Primitive Irish Old Irish Primitive Irish Old Irish
"he refuses" *uss ˈbond-et(i) as·boind *nís ˈuss-bond-et(i) ní op(a)ind /obǝnʲdʲ/ *uss 'bod-s-t as·bó *nís ˈuss-bod-s-t ní op /ob/
"he remains over" *di ˈwo-uss-ret-et(i) do·fúarat *nís ˈdi-wo-uss-ret-et(i) ní díurat *di ˈwo-uss-ret-s-t do·fúair *nís ˈdi-wo-uss-ret-s-t ní diúair
"he repeats, amends" *ad ˈess-reg-et(i) ad·eirrig *nís ˈ*ad-ess-reg-et(i) (ní aithrig?? >) ní aithirrig *ad ˈess-reg-s-t ath·e(i)rr *nís ˈad-ess-reg-s-t ní aithir
"he can" *con ˈink-et(i) com·ic *nís ˈcom-ink-et(i) ní cum(a)ic > ní cum(u)ing, ní cumaing *con ˈink-s-t con·í *nís ˈcom-ink-s-t, *nís ˈcom-ink-ā-t ní cum, ní cumai
"it happens" *ad ˈcom-ink-et(i) (ad·cum(a)ic >) ad·cumaing *nís ˈad-com-ink-et(i) (ní ecm(a)ic >) ní ecmaing *ad ˈcom-ink-ā-t ad·cumai *nís ˈad-com-ink-ā-t ní ecm(a)i

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. That is, 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 this occurred only when the nasal had not previously been joined to a following voiced stop as a result of nasal assimilation; c.f. frecnd(a)irc "present" (disyllabic).
    • Remaining impossible clusters were generally simplified by deletion of consonants non-adjacent to vowels (e.g. between other consonants). Note, however, that Old Irish tolerated geminates adjacent to other consonants as well other quite complex clusters, including e.g., ainm /aNʲm/ "name" (one syllable), fedb /fʲeðβ/ "widow", do-aidbdetar /do-ˈaðʲβʲðʲǝdǝr/ "they are shown".[20]

Proto-Celtic short vowels, vowel affection

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

However, during the run-up to Old Irish a number of mutations (umlauts) take place, where former vowels are modified in various ways depending on following vowels (or sometimes surrounding consonants). These mutations are known in Celtic literature as affections or infections, of which the most important are:[21]

  1. i-affection: Short *e and *o are raised to i and u when the following syllable contains a high vowel (*i, *ī, *u, *ū). 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, *ā, *o, *ō[clarification needed]).
  3. u-affection: Short *a, *e, *i are broken to short diphthongs au, eu, iu when the following syllable contains a *u or *ū that was later lost. It is assumed that, at the point this change operated, u-vowels that were later lost were short *u, while those that remain were long *ū. This change operates after i-affection; hence, original *e may end up as iu.

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

  • sen "old (nom. sg.)" < *senos, but sin "old (gen. sg.)" < *senī (i-affection), siun "old (dat. sg.)" < *senu (i-affection and u-affection) < *senū < PIE *senōi, sinu "old (acc. pl)" < *senūs (i-affection but no u-affection because the u remains) < PIE *senons.
  • fer "man (nom. sg.)" < *wiros (a-affection), but fir "man (gen. sg.)" < *wirī (no a-affection), fiur "man (dat. sg.)" < *wiru (u-affection) < *wirū < PIE *wirōi, firu "men (acc. pl)" < *wirūs (no u-affection because the u remains) < PIE *wirons.
  • nert "strength (nom. sg.)", but neurt "strength (dat. sg.)" < *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 (nom. sg.)" < *wirtus (u-affection; from Latin virtus), fert(a)e "miracle (nom. pl.)" < *wirtowes.

Verbal paradigm example:

form Pronunciation Meaning Prim Irish Post-PIE Comments
Absolute 1sg biru /bʲiru/ "I carry" *berūs *bʰerō + -s i-affection
Absolute 2sg biri /bʲirʲi/ "you (sg.) carry" *berisis *bʰeresi + -s i-affection (unstressed *-es- > *-is- in Primitive Irish; also found in s-stems)
Absolute 3sg berith /bʲirʲǝθʲ/ "he carries" *beretis *bʰereti + -s Unstressed i = /ǝ/ with surrounding palatalised consonants; see #Orthography
Conjunct 1sg ⋅biur /bʲĭŭr/ "I carry" *beru < *berū *bʰerō i-affection + u-affection
Conjunct 2sg bir /bʲirʲ/ "you (sg.) carry" *beris < *berisi *bʰeresi i-affection (unstressed *-es- > *-is- in Primitive Irish)
Conjunct 3sg beir /bʲerʲ/ "he carries" *beret < *bereti *bʰereti i in ei signals palatalisation of following consonant; see #Orthography

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 (e.g. sen < *senos and fer < *wiros have identical declensions). Note however the cases of nert vs. fiurt above, where i-affection but not a-affection was blocked by intervening rt.

Proto-Celtic long vowels and diphthongs

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

Proto-Celtic archaic Old Irish later Old Irish Example(s)
í (gen. ríg) ‘king’ (cf. Latin rēx, Sanskrit rājan-)
rím ‘number’ (cf. OHG rīm, Latin rītus ‘rite’)
á máthir ‘mother’ (cf. Latin māter)
dán ‘gift’ (cf. Latin dōnum)
ú cúl ‘back’ (cf. Latin cūlus ‘ass, buttocks’)
*ai /ai/ (spelled áe or ) merged (both spellings used) cáech ‘one-eyed’ < PIE *káikos (cf. Latin caecus ‘blind’, Gothic háihs ‘one-eyed’)
*oi /oi/ (spelled óe or ) oín, óen ‘one’ < PIE *oinos (cf. archaic Latin oenos)
*ei > ē é ía ⋅tíagat ‘they go’ < archaic ⋅tégot < PIE *steigʰ- (cf. Ancient Greek steíkhein ‘to walk’, Gothic steigan ‘to go up’)[22]
*au (+C)[* 5] > ō ó úa úaithed, úathad ‘singleness’ < IE *h₂eu ‘again’ + *to- ‘that’ (cf. Ancient Greek autós ‘self’)
*eu/ou (+C)[* 5] > ō núa, núë ‘new’ < archaic núae < PC *noujos (cf. Gaulish novios) < IE *neu-io-s (cf. Gothic niujis)
túath ‘tribe, people’ < PC *toutā < IE *teutā (cf. Gothic þiuda)
rúad ‘red’ < PC *roudos < PIE *h₁reudʰ- (cf. Gothic rauþs)
*au (not +C)[* 6] áu ó ó < archaic áu, aue ‘ear’ < PC *ausos < IE *h₂eus- (cf. Latin auris)
< archaic náu ‘ship’ < PC *nāwā < PIE *neh₂u- (cf. Latin nāvis)
*ou (not +C)[* 6] óu > áu ‘cow’ < archaic báu < early archaic bóu (c. a.d. 700) < PC *bowos (gen.sg.) < PIE *gʷh₃-eu-

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 non-archaic Old Irish are due to compensatory lengthening of short vowels before lost consonants, or to the merging of two short vowels in hiatus, e.g. cét /kʲeːd/ ‘hundred’ < Proto-Celtic kantom (cf. Welsh cant) < PIE *kṃtóm.

PIE consonants


See Proto-Celtic for various changes that occurred in all the Celtic languages, most notably:

  • 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:

  • 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 (e.g. 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, e.g. béu béo "living, alive" < *bewas < *biwos < *gʷiwos.[23] 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, e.g. 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:[24]

  • 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:[25]

  • *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.[* 7]

Intervocalic clusters

A large number of 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/; similarly for *nk. E.g. 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").[26]
  • *ns > unlenited s with compensatory lengthening of a preceding vowel; *ans > *ens > és similarly to *ant *ank; e.g., géis "swan" < PCelt *gansi- < PIE *ǵʰh₂ens- (cf. Dutch gans "goose").

Cluster reduction involving *s *z:

  • Medial *sm *sn *sl > mm nn ll. E.g. 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/; e.g., net /nedd/ "nest" < PIE *nisdos /nizdos/.

Lenited stops *x *ɣ *θ *ð 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 (e.g. ad-) . Examples:[6]

  • 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).

But *θr, *βr, *βl survive, e.g. críathraid "he perforates" < PCelt *krētrāti-s; gabur "goat" < PCelt *gabros (cf. Welsh gafr); mebul "shame" (cf. Welsh mefl).



Old Irish had three genders, namely, masculine, feminine and neuter; three numbers, namely, singular, dual and plural, with the dual being attested only to a limited degree with somewhat distinct forms, though it is almost always preceded by the cardinal , meaning "two" (and as such has been retained in the modern Gaelic languages); and five cases (nominative, vocative, accusative, genitive and dative). Thurneysen had fourteen classes of noun, defined by the morphological marking on the stem, with seven vocalic stems and seven consonantal stems (including one class of irregular and indeclinable nouns). The full range of case is only evident in the noun phrase, where the article causes noun initial mutation, and where the initials of following adjectives are mutated according to the underlying case ending, thus in fer becc "the small man", nominative, differs from the accusative in fer /βer/ m-becc, though at times such mutations were not written. In the following, L shows lenition of the following adjective, N shows nasalisation (eclipsis) of the following adjective, and H shows prefixing of h to following vowel initial adjectives. (These mutations are related to the form of the case ending in Common Celtic. Endings with a final vowel triggered lenition; those with a final nasal consonant triggered eclipsis; and those with a final /s/ triggered prefixing of h. For the most part, the endings that can be reconstructed by these mutations agree with the corresponding forms in Sanskrit, Ancient Greek and/or Latin.)

Feminine ā-stems Singular Dual Plural
Nominative/Vocative túath L túaithL túatha(H)
Accusative túaithN
Genitive túaithe(H) túathL túathN
Dative túaithL túath(a)ib
Masculine o-stems Singular Dual Plural
Nominative fer ferL firL
Vocative firL firu(H)
Accusative ferN
Genitive firL ferN
Dative fiurL fer(a)ib
Neuter o-stems Singular Dual Plural
Nominative/Vocative/Accusative scélN scélL; scéla(L)
Genitive scéuil/scéoilL scélN
Dative scéulL scél(a)ib


Verbs stand initially in the sentence (preceded only by some particles, forming a "verbal complex", and very few adverbs). The verb can be either suffixed for tense, person, mood and aspect (often portmanteau suffixes), or these can be shown by vowel changes in the stem (e.g. as·beir present "says", as·rubart past "said", as·béra future "will say"). Before this core "verb phrase" are placed various other preverbal clitic particles, e.g. negative ni-/ní-, perfective ro- or one or more preverbal particles that modify the meaning of the verb in unpredictable ways (compare ā-, ex-, in-, dē-, etc. in Latin verbs). Personal pronouns as direct objects are infixed between the preverb and the verbal stem. In an overall sense, the verb structure is agglutinative. A single verb can stand as an entire sentence in Old Irish, in which case emphatic particles such as -sa and -se are affixed to the end of the verb.

Verbs are conjugated in present, imperfect, past, future and preterite tenses; indicative, subjunctive, conditional and imperative moods; and active and passive voices. The only verbal form lacking in Old Irish is the infinitive, this covered, as in the modern Gaelic languages, by the verbal noun. Old Irish inherits a large amount of Indo-European verbal morphology, including:

Most verbs have, in addition to the tenses, voices, and moods named above, two sets of forms: a conjunct form, and an absolute form. The absolute form occurs when the verb occurs absolutely sentence-initial with no preverbs, while the conjunct form occurs when the verb is preceded by one or more preverbs. Absolute and conjunct forms are distinguished primarily by the endings. In addition, the conjunct form comes in two variants, deuterotonic ("second-stressed", when exactly one preverb precedes and the stress is on the first syllable of the verbal stem) and prototonic ("first-stressed", when more than one preverb precedes and the stress is on the second preverb). These variants are marked by (sometimes radical) changes in the verbal stem and non-initial preverbal particle(s), which merge with the stem. This is due to the Celtic version of Wackernagel's law, where stress falls in second position whenever there is one or more preverbs.

The difference between absolute and conjunct endings is thought to reflect an additional particle *-es added to the absolute verbal form.[27] Final -i in the conjunct forms was apparently lost early on (cf. a similar change in Latin).

See below for an example of absolute vs. conjunct endings, and deuteronic vs. prototonic stems.

Present tense

The following is an example of a strong present-tense verb (class B I), showing the absolute, conjunct deuterotonic and conjunct prototonic forms.

Conjugation of berid "he carries", do⋅beir "he gives, brings" < *to-beret(i), ní-tab(a)ir "he does not give, bring" < *nís to-beret(i), as⋅beir "he says" < *ess-beret(i), ní-ep(a)ir "he does not say" < *nís ess-beret(i)
Absolute Conjunct
Deuterotonic Prototonic
Old Irish PCelt Old Irish PCelt Old Irish
1st Sing biru *berū-s do⋅biur as⋅biur *-berū ní-tabur ní-epur
2nd Sing biri *beresi-s do⋅bir as⋅bir *-beres(i) ní-tab(a)ir ní-ep(a)ir
3rd Sing berid, -ith *bereti-s do⋅beir as⋅beir *-beret(i) ní-tab(a)ir ní-ep(a)ir
1st Pl berm(a)i *beromos-es do⋅beram as⋅beram *-beromos ní-taibrem ní-eprem
2nd Pl *beirthe *beretes-es[28] do⋅berid, -ith as⋅berid, -ith *-beretes[28] ní-taibrid, -ith ní-eprid, -ith
3rd Pl ber(a)it *beronti-s do⋅berat as⋅berat *-beront(i) ní-taibret ní-epret

The following present-tense formations existed:

Weak verbs:

  • A I: a-presents (e.g. mór(a)id "he magnifies", conjunct ·móra), with a suffix *-ā- < PIE *-eh₂ (cf. Latin -āre)
  • A II: i-presents (e.g. lé(i)cid "he leaves", conjunct ·lé(i)ci), with a suffix *-ī- < PIE causative *-éye- with o-grade, PIE denominative *-eyé-, PIE stative *-eh₁ (cf. Latin -ēre, -īre)
  • A III: hiatus verbs (e.g. raïd/ráïd "he rows", conjunct ·rá; gniïd/gníïd "he does"), with a root that synchronically ends with a vowel

Strong verbs:

  • B I: Verbs with alternating root-final broad/slender quality (e.g. berid "he carries", agid "he drives", canid "he sings") < PIE simple thematic verbs
  • B II: Verbs originally with consistent root-final slender quality (e.g. a(i)rid "he plows", ga(i)bid "he takes", gu(i)did "he prays") < PIE thematic verbs in *-y-
  • B III: Verbs with n-infix (e.g. bongid "he breaks", with reduplicated preterite bobag-) < PIE n-infix verbs
  • B IV: Verbs with broad n-suffix (e.g. cren(a)id "he buys", cf. Sanskrit krīṇā́ti, 3rd sing. subjunctive ·cria) < PIE -neh₂- verbs
  • B V: Verbs originally with alternating broad/slender n-suffix (e.g. ara·chrin "he decays", pl. ara·chrinat) < PIE -neu-/-nu- verbs

Other forms

The subjunctive comes in two variants:

  • a-subjunctive (cf. Latin subjunctives in -ā-)
  • s-subjunctive, apparently < PIE s-aorist subjunctive

In the s-subjunctive, the s is attached directly to the root. The endings are partly athematic, especially the 3rd singular, with original suffix *-s-t that leads to truncation of the root: cf. as·boind "he refuses" < *uss-ˈbond-et, prototonic ·op(a)ind < *ˈuss-bond-et; subj. as·bó < *uss-ˈbod-s-t, prototonic ·op /ob/ < *ˈuss-bod-s-t; 2 sg. subj. as·bóis < *uss-ˈbod-s-es, prototonic ·obbais < *ˈuss-bod-s-es with thematic *-s-es.[* 8]

The imperfect is built off the same stem as the present, but with different endings. The same endings are used in the past subjunctive, attached to the present subjunctive stem.

The future comes in four variants:

  • f-future, made to weak verbs;
  • reduplicated a-future;
  • é-future (é replaces verb-stem vowel);
  • reduplicated s-future (cf. Sanskrit desiderative jighāṃsati "he wants to kill" < PIE *gʷhi-gʷhn̥-h₁s-eti, root *gʷhen-).

The preterite comes in four variants:

  • s-preterite;
  • t-preterite;
  • reduplicated suffixless preterite;
  • non-reduplicated suffixless preterite.


Old Irish follows the typical VSO (verb-subject-object) structure shared by most Insular Celtic languages (even though other orders are possible, especially under Bergin's Law). Verbs are all fully conjugated, and have most of the forms typical of Indo-European languages (see above). Personal pronouns, when used as direct objects, are prefixed to the verb with which they are associated (after other prefixes, and therefore are often referred to as infixes). Prepositions have the same status as the Latin prepositions, including the property of being verb prefixes.

See also


  1. Primitive Irish *di-s-ro-uss-skokīt vs. *nī-s-di-ro-uss-skokīt, *embi-s-sawet vs. *nī-s-embi-sawet, with the stressed syllable underlined.
  2. 2.0 2.1 2.2 2.3
    • ingen /inʲɣʲǝn/ "daughter" < Ogam inigena < Proto-Celtic *eni-genā (cf. Latin indigenā "(female) native", Ancient Greek engónē "granddaughter".
    • ingen /iNʲɡʲǝn/ "claw, nail" < Proto-Celtic *angʷīnā < PIE *h₃ṇgʷh- (cf. Latin unguis).
  3. Per Sihler 1995, Ringe 2006; *eso according to Beekes 1995. See footnote for genitive plural.
  4. The PIE form of the genitive plural (both ending and stem) is somewhat unclear. The ending is traditionally reconstructed as *-ōm, but Ringe (2006: 56) reconstructs *-oHom, while both Sihler (1995: 391) and Beekes (1995: 213, 229) reconstruct *-om. Ringe and Sihler both reconstruct a masculine/neuter stem *eys-, while Beekes reconstructs *es-. Sihler and Beekes both reconstruct the feminine stem as identical to the masculine stem (*eys- for Sihler, *es- for Beekes), while Ringe reconstructs a separate feminine stem *ih₂s-. These differences are based on the divergent attested outcomes, with the various scholars differing as to which parts of which attested forms are inherited and which are due to analogy.
  5. 5.0 5.1 When followed by a consonant in Old Irish.
  6. 6.0 6.1 When not followed by a consonant in Old Irish. This includes words originally followed by *s, which was lost by Old Irish times.
  7. Originally a neuter proterokinetic noun of the form *gʷenh₂ (nom. sg.), *gʷneh₂s (gen. sg.). The original PIE nominative is still preserved in poetic/legal Old Irish N "woman" (still neuter!) < Proto-Celtic *ben < PIE *gʷenh₂. The normal Old Irish nominative is benL (feminine) < Proto-Celtic *benā < *ben + normal feminine *-ā. No other IE language preserves the original neuter gender.
  8. The root of this verb is *bod-, originally *bud- < PIE *bhudh- (cognate with Old English bēodan "to offer, announce", Sanskrit bodhati "to awaken, inquire"); the variant *bod- occurred in the present indicative through a-infection and was generalised. The *-n- is a present-tense infix (cf. the cognate Ancient Greek verb punthánomai "I inquire", aorist eputhómēn "I inquired").


  1. Nordhoff, Sebastian; Hammarström, Harald; Forkel, Robert; Haspelmath, Martin, eds. (2013). "Old Irish (to 900)". Glottolog. Leipzig: Max Planck Institute for Evolutionary Anthropology.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. 2.0 2.1 Koch, John Thomas (2006). Celtic culture: a historical encyclopedia. ABC-CLIO. p. 831. The Old Irish of the period c. 600–c. 900 AD is as yet virtually devoid of dialect differences, and may be treated as the common ancestor of the Irish, Scottish Gaelic, and Manx of the Middle Ages and modern period; Old Irish is thus sometimes called 'Old Gaelic' to avoid confusion.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. Ó Baoill, Colm (1997). "13: The Scots-Gaelic Interface". The Edinburgh History of the Scots Language. Edinburgh University Press. p. 551. The oldest form of the standard that we have is the language of the period c. AD 600–900, usually called 'Old Irish' – but this use of the word 'Irish' is a misapplication (popular among English-speakers in both Ireland and Scotland), for that period of the language would be more accurately called 'Old Gaelic'.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. Thurneysen 1946, p. 4.
  5. Kortlandt 2007, p. 8.
  6. 6.0 6.1 Thurneysen 1946, p. 79.
  7. Thurneysen 1946, p. 32.
  8. Kortlandt 2007.
  9. Greene 1973.
  10. Thurneysen 1946, p. 18.
  11. Thurneysen 1946, p. 137.
  12. Thurneysen 1946, p. 181.
  13. Thurneysen 1946, p. 58.
  14. Thurneysen 1946, p. 98.
  15. Thurneysen 1946, pp. 192–193.
  16. Thurneysen 1946, p. 42.
  17. Sihler 1995, p. 391.
  18. Thurneysen 1946, p. 68.
  19. Fortson 2004, p. 324.
  20. Thurneysen 1946, pp. 70,100.
  21. Thurneysen 1946, pp. 46–50,57.
  22. Thurneysen 1946, p. 36.
  23. Thurneysen 1946, p. 125.
  24. Thurneysen 1946, pp. 128–140.
  25. Thurneysen 1946, pp. 123–139.
  26. Thurneysen 1946, pp. 126–127.
  27. Thurneysen 1946, p. 363.
  28. 28.0 28.1 Sihler 1995, p. 465.


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