Old Irish grammar

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This article describes the grammar of the Old Irish language.

Grammatical processes[edit]

Initial mutations[edit]

In the system of initial consonant mutations, the initial consonant of a word is modified in one or another way, depending on the nature of the preceding word: la tech /la tʲex/ "towards a house" vs. fo thech /fo θʲex/ "under a house", i tech /i dʲex/ "into a house", with the alternation /t ~ θ ~ d/ in the initial consonant of tech "house" triggered by the preceding preposition.

There are three types of mutation:

  • Lenition, a weakening of the initial consonant. This generally turns plosives into fricatives, among other effects.
  • Nasalisation, originally a prepending of a nasal consonant to the word, which caused further changes.
  • Aspiration and gemination, causing either gemination of the initial consonant, or the insertion of /h/.

The mutations became an important part of the grammar and remain, with little change, in Modern Irish (see Irish initial mutations). They were often crucial in distinguishing various grammatical forms, which would be homophones if not for the mutations. For example, in the case of the possessive determiner a, only the initial mutation of the following word distinguishes the meanings "his", "her", and "their":

Meanings distinguished by initial mutations
No change Lenition Nasalization Aspiration/gemination
ech /ex/ "horse" a ech /a ex/ "his horse" a n-ech /a nex/ "their horse" a ech /a hex/ "her horse"
bo /bo/ "cow" a bo /a vo/ "his cow" a m-bo /a mbo/ "their cow" a bo /a bbo/ "her cow"
tech /tʲex/ "house" a thech /a θʲex/ "his house" a tech /a dʲex/ "their house" a tech /a ttʲex/ "her house"
fer becc /fʲer bʲeɡ/ "small man" (nominative) dá fer becc /daː er vʲeɡ/ "two small men" (nominative) fer m-becc /fʲer mbʲeɡ/ "small man" (accusative)

Another grammatical feature signalled by mutations is relative clause attachment, in which 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).

In general, there is no way to predict from the form of a given word the type of mutation that 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).

Initial mutations were originally sandhi effects, and depended on the shape of the original final syllable in Primitive Irish. It was grammaticalised by the loss of final syllables in the transition from Primitive Irish to Old Irish. In Old Irish, the process was already grammatical to a large degree, and was limited to applying across words within a single syntactic phrase (e.g. between a noun and a modifying adjective, or between a preposition and the rest of the prepositional phrase). Initial mutations did not apply across phrase boundaries generally, but there are some instances where this does occur in the earliest Old Irish attestations.


Lenition is the weakening of a consonant according to a particular pattern. It applied to consonants appearing between vowels in Primitive Irish. When a preceding word ended in a vowel, the first consonant of the following word was lenited.

Lenition was not indicated in the spelling except in the case of initial voiceless stops, which were written ph th ch when lenited. In later Old Irish, initial f s come to be written ḟ ṡ when lenited, with a dot (a so-called punctum delens) above the letter.

Lenition occurs after:

  • Certain case forms within a noun phrase, either of the noun or a preceding article or possessive. These include, at least:
    • Nominative and vocative singular of all feminines
    • Dative singular of all genders
    • Nominative, vocative, accusative and genitive dual of all masculines and feminines
    • Nominative, vocative and accusative plural of all neuters (but inconsistently after -a)
  • Certain prepositions
  • Certain conjunctions
  • Certain infixed pronouns


Nasalisation, also known as eclipsis in Modern Irish grammar, is the prepending of a nasal consonant to the word. It was caused by a preceding word ending in a nasal consonant. Due to later changes involving clusters of nasals and other consonants, in particular the coalescing of nasal-stop clusters to voiceless plosives (such as /nt/ > /d/), nasalisation may also manifest itself as voicing in Old Irish.

Nasalisation was not indicated in the spelling except for initial voiced stops and vowels, where n- is prefixed (m- before b).

Nasalisation occurs after:

  • Certain case forms within a noun phrase, either of the noun or a preceding article or possessive. These include, at least:
    • Nominative, vocative and accusative singular and dual of all neuters
    • Accusative singular of all masculines and feminines
    • Genitive plural of all genders
  • Certain prepositions
  • Certain conjunctions
  • Certain infixed pronouns

Aspiration and gemination[edit]

Originally two different effects, aspiration and gemination came to be triggered in the same environments and thus can be treated as one type of mutation.

Aspiration involved prepending an additional /h/ to a vowel-initial word. It was primarily caused by syllables formerly ending in /s/, which lenited to /h/ between vowels. In gemination, an initial consonant was geminated by a preceding word originally ending in /k/, /s/ or /t/ after a vowel. By analogy, words originally ending in /k/ and /t/ came to aspiration before vowel-initial words as well.

Gemination was only occasionally indicated, and as geminated consonants were in the process of reducing to single consonants in Old Irish times, the mutation effect itself was waning. Aspiration was not indicated at all.

Aspiration/gemination occurs after:

  • Within a noun phrase, either of the noun or a preceding article or possessive, all forms that end in a vowel but do not trigger lenition or nasalisation. This includes, at least:
    • Genitive singular of all feminines
    • Vocative and accusative plural of all genders
  • Certain prepositions
  • and ba


Palatalisation as such is phonological, but it also has a grammatical aspect to it. Certain case forms of nouns automatically trigger palatalisation of the final consonant of a word, as do forms of verbs. Consequently, the quality of the final consonant can often vary between different forms of the same word.

Palatalisation also occurs when a syllable that originally contained a front vowel undergoes syncope. Since Old Irish generalised the palatal or nonpalatal quality across an entire consonant cluster, when the front vowel was lost, the palatalisation of the preceding consonants "extended" to the entire resulting consonant cluster, consisting of both the consonants before the syncopated vowel and the consonants after it. This could lead to alternations between palatalisation in the syncopated forms and nonpalatalisation in the unsyncopated forms of a word. For example, the noun dorus /ˈdorus/ "door" originally had a front vowel e in the second syllable (Proto-Celtic *dworestu), but this did not cause palatalisation due to the u-affection of the final vowel. However, when the noun was syncopated in certain case forms, the palatalisation reappeared and spread also to the final s, seen in the genitive singular doirseo /ˈdorʲsʲo/ and dative plural doirsib /ˈdorʲsʲəvʲ/.

Palatalisation can sometimes affect the immediately preceding vowel:

  • íaé.
  • áe, óe, . This is purely an orthographical distinction, and is not adhered to strongly in the manuscripts. It's used more often in normalised spellings for clarity.

Vowel affection[edit]

Vowel affection is the changing of the height of a vowel to more closely match the height of the vowel in a following syllable. It is similar to Germanic umlaut, but more pervasive. It was originally a relatively automatic process, but because the final vowels were later mostly lost in the transition to Old Irish, the process became unpredictable and grammaticalised. Three different kinds of vowel affection existed in Old Irish, lowering, raising and u-insertion.

Lowering was caused by a (former) low vowel a or o in the following syllable, and affected the underlying short vowels i and u, changing them to e and o respectively. It occurred regardless of the preceding consonants, and was thus rather common.

Raising was the reverse development: when followed by a (former) high vowel, short i or u, in the following syllable, the vowels e and o were changed to i and u. It did not occur in all cases, as it was limited by the intervening consonants. It occurred only when at most one consonant stood between the syllables, and the consonant had to be voiced (this included sonorants). Thus, while the noun cenn /kʲeN/ was raised to cinn /kʲiNʲ/ in the genitive singular form (along with palatalisation), ech /ex/ was not raised and retained its original vowel in its genitive singular form eich /exʲ/.

The underlying vowel of a word remained when the vowel e formerly followed. For example, in masculine o-stems, the vocative singular form had e in the ending, but the other forms had other vowels which caused either raising or lowering. In neuter o-stems, all forms had raising or lowering endings, none originally contained e. This can make it difficult to ascertain what the original underlying vowel was.

U-insertion was a third effect, caused by a (formerly) following u. It involved inserting the vowel u (or o, as an orthographic variant) after an existing vowel, and occurred with the long vowel é and the short vowels a, e and i. The results were as follows:

  • aau.
  • eiu if raising can take place, eu/eo otherwise.
  • iiu.
  • ééu/éo, sometimes also íu.

U-insertion did not necessarily occur in all cases where it might be expected, in particular when the u that might cause the effect was still present. For example, the accusative plural of ech may be euchu/eochu, but echu is also found, lacking u-insertion. For fer, the accusative plural is firu, never *fiuru.


Old Irish has 3 genders: masculine, feminine and neuter; 3 numbers: singular, dual and plural; and 5 cases: nominative, vocative, accusative, genitive and dative. The dual is predominantly preceded by the cardinal number "two". The full range of forms 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, though at times such mutations were not written. In the following, L shows lenition, N shows nasalisation, and H shows aspiration/gemination. In addition, there was some syncretism in forms regardless of mutations: certain forms were always identical. These were:

  • Nominative/vocative/accusative of all neuter nouns in all numbers.
  • Nominative/vocative/accusative dual of all nouns.
  • Vocative/accusative plural of all nouns.
  • Dative dual/plural of all nouns.


The o-stems could be masculine or neuter, and were the most widespread kind of noun, thus this class is well attested. They descend from the Proto-Indo-European thematic inflection.

Masculine o-stems
Singular Dual Plural
Nominative fer ferL firL
Vocative firL firuH
Accusative ferN
Genitive firL ferN
Dative fiurL feraib

In the neuter variant, the genitive and dative forms were the same as those of the masculine variant, while the nominative, vocative and accusative differed.

Neuter o-stems
Singular Dual Plural
Nominative scélN scélN scélL, scéla(L)
Genitive scéilL scélN
Dative scéulL scélaib


The io-stems were originally simply o-stems with a /j/ before the endings. Later sound changes deleted this consonant, but its presence caused some of the case endings to be preserved where they were deleted in the plain o-stem inflection. The final consonant is either always palatalised, or never.

Masculine io-stems
Singular Dual Plural Singular Dual Plural
Nominative céileH céileL céiliL daltaeH daltaeL daltaiL
Vocative céiliL céiliuH daltaiL daltuH
Accusative céileN daltaeN
Genitive céiliL céileN daltaiL daltaeN
Dative céiliuL céilib daltuL daltaib
Neuter io-stems
Singular Dual Plural Singular Dual Plural
Nominative crideN crideN crideL cumachtaeN cumachtaeN cumachtaeL
Genitive cridiL crideN cumachtaiL cumachtaeN
Dative cridiuL cridib cumachtuL cumachtaib


The ā-stems were always feminine, and were the most common type of feminine noun.

Feminine ā-stems
Singular Dual Plural
Nominative túathL túaithL túathaH
Accusative túaithN
Genitive túaitheH túathL túathN
Dative túaithL túathaib


The iā-stems were originally a variant of the ā-stems, but were preceded by a /j/ which caused changes similar to those in the io-stem inflection. Again, the final consonant could be always palatalised, or never.

Feminine iā-stems
Singular Dual Plural Singular Dual Plural
Nominative guideL guidiL guidiH ungaeL ungaiL ungaiH
Accusative guidiN ungaiN
Genitive guideH guideL guideN ungaeH ungaeL ungaeN
Dative guidiL guidib ungaiL ungaib


The ī-stems were always feminine, and were a variant of the iā-stem inflection in which a few case forms lacked an overt ending. In these forms, the final consonant was always palatalised. The forms with an ending could be either palatalised or not, depending on the noun. The ī-stem inflection continues the so-called devī- or ī/yā-inflection of Proto-Indo-European.

There were two sub-variants. The original, "long" variant had endings in the accusative and optionally in the dative singular, while the newer "short" variant had no ending and only palatalisation in these forms, by analogy with the ā-stems.

Feminine ī-stems
Singular Dual Plural Singular Dual Plural
Nominative rígainL rígainL rígnaiH aithisL aithisL aithisiH
Accusative rígnaiN aithisN
Genitive rígnaeH rígnaeL rígnaeN aithiseH aithiseL aithiseN
Dative rígainL, rígnaiL rígnaib aithisL aithisib


The i-stems could have any gender. The masculine and feminine variants were identical except for one detail: the nominative singular of feminine i-stems caused lenition, while it did not for masculine i-stems. The plural forms could either be always palatalised, or never (depending on the noun), while in the singular and dual, the palatalisation depended on the ending.

Masculine/feminine i-stems
Singular Dual Plural Singular Dual Plural
Nominative cnáim cnáimL cnámaiH súilL súilL súiliH
Vocative cnáimL
Accusative cnáimN súilN
Genitive cnámo, -aH cnámo, -aL cnámaeN súlo, -aH súlo, -aL súileN
Dative cnáimL cnámaib súilL súilib

Neuter i-stems were relatively rare. Like in the o-stems, only the nominative, vocative and accusative differed from the masculine variety, while the genitive and dative forms were the same.

Neuter i-stems
Singular Dual Plural
Nominative muirN muirN muireL
Genitive moro, -aH moro, -aN muireN
Dative muirL muirib


The u-stems could be masculine or neuter. Feminine u-stem nouns had originally existed, but they had all been converted into ā-stems by the time Old Irish was written. None of the endings triggered palatalisation. However, palatalisation did occur when a syllable (formerly) containing a front vowel was contracted.

Masculine u-stems
Singular Dual Plural
Nominative guth guthL gothae, -ai, -aH
Vocative guthuH
Accusative guthN
Genitive gotho, -aH gotho, -aL gothaeN
Dative guthL gothaib

Neuter u-stems were not very common. The genitive and dative forms were the same as in the masculine variety.

Neuter u-stems
Singular Dual Plural
Nominative dorusN dorusN dorusL, doirsea
Genitive doirseo, -aH doirseo, -aN doirseN
Dative dorusL doirsib

Velar stems[edit]

The velar stems, also called "guttural stems", belonged to the larger class of "consonant stems", which mostly shared the same endings. They were masculine or feminine, and had a stem ending in a velar consonant, ch, g (/ɣ/) or c /ɡ/. The final consonant itself was lost in the nominative and vocative singular. Word-final palatalised -ich was voiced to -ig, partially merging the two types.

Masculine/feminine velar stems
Singular Dual Plural Singular Dual Plural Singular Dual Plural
Nominative sail sailigL sailig H rígL ríg lie, liaH liicL lieic, liaic, liic
Vocative sailcheaH rígaH *lie, *liaH leccaH
Accusative sailigN rígN lieic, liaic, liicN
Genitive sailech sailechL sailechN ríg rígL rígN liac(c) *lieic, *liaic, *liicL liac(c)N
Dative sailigL, sailL sailchib rígL, L rígaib lieic, liaic, liicL *lecaib

Dental stems[edit]

The dental stems were also consonant stems, and had a stem ending in a dental consonant, th, d (/ð/) or t (/d/). The final consonant itself was lost in the nominative and vocative singular. Unstressed word-final -th was generally converted to -d early on, so that the two types became indistinguishable in most forms.

Masculine/feminine dental stems
Singular Dual Plural Singular Dual Plural Singular Dual Plural
Nominative cing cingid, -thL cingid, -th araeH araidL araid caraeH caraitL carait
Vocative cingtheaH aradaH, araduH cairtea, -deaH
Accusative cingid, -thN araidN caraitN
Genitive cinged, -th cinged, -thL cinged, -thN arad aradL aradN carat caratL caratN
Dative cingid, -thL, cingL cingthib araidL, araeL aradaib caraitL cairtib, -dib

Only a few neuters existed.

Neuter dental stems
Singular Dual Plural
Nominative détN détN détL
Genitive dét ? détN
Dative déitL détaib


The r-stems were limited to a handful of words for family members. The final -r was preserved throughout the paradigm, and all but one had th before the r.

Masculine/feminine r-stems
Singular Dual Plural Singular Dual Plural
Nominative máthair *máthairL máithir siur sieirL seithir
Vocative máithreaH sethraH
Accusative máthairN sieirN, siairN
Genitive máthar *mátharL máithreN, máthraeN sethar *setharL setharN
Dative máthairL máithrib, máthraib sieirL, siairL sethraib


The s-stems were all neuter, with one exceptional "ns-stem", which was masculine. The final consonant had disappeared everywhere, leaving the name a bit of a misnomer. The class is called "s-stem" because of its relationship to nouns of this class in other Indo-European languages.

Neuter s-stems
Singular Dual Plural Singular Dual Plural
Nominative nemN nemN nimeL tegN, techN tegN, techN tigeL, taigeL
Genitive nimeH nimeL nimeN tigeH, taigeH tigeL, taigeL tigeN, taigeN
Dative nimL nimib tigL, taigL tigib, taigib

In the sole masculine noun of this class, the s actually does surface in most forms.

Masculine s-stems
Singular Dual Plural
Nominative H L mís
Vocative *H mísaH
Accusative mísN
Genitive mís mísN
Dative mísL, L mísaib


The n-stems were masculine, feminine or neuter, though the neuters behaved differently from the masculines and feminines. There were several subclasses among the masculine and feminine n-stems:

  • Lenited final n
    • Final vowel in nominative singular
    • No final vowel in nominative singular
  • Unlenited n(n)

The nouns with lenited final n included agent nouns ending in -am/-em, among other nouns. The nominative singular could be either endingless or end in -u or -e; those with a vowel had three possible dative singular forms.

Masculine/feminine n-stems, lenited
Singular Dual Plural Singular Dual Plural
Nominative talam talmainL talmain toimtiuH toimtinL toimtin
Vocative talmanaH toimtenaH
Accusative talmainN toimtinN
Genitive talman talmanL talmanN toimten toimtenL toimtenN
Dative talmainL, talamL talmanaib toimteL, toimtiuL, toimtinL toimtenaib

The nouns with unlenited -n(n) inflected as follows:

Masculine/feminine n-stems, unlenited
Singular Dual Plural
Nominative gobaeH gobainnL gobainn
Vocative goibneaH
Accusative gobainnN
Genitive gobann gobannL gobannN
Dative gobainnL, gobaeL goibnib

The neuters of this class continued the Indo-European proterokinetic neuters in *-men-. Consequently, they almost all ended in -m(m) in Old Irish.

Neuter n-stems
Singular Dual Plural Singular Dual Plural
Nominative céimmN céimmN céimmennL ainmN ainmN anmannL
Genitive céimmeH ? céimmennN anmaeH ? anmannN
Dative céimmimmL, céimmL céimmennaib anmaimmL, ainmL anmannaib

Irregular nouns[edit]


Adjectives agree with nouns in case, gender, and number, and have positive, comparative, and superlative forms. Demonstrative adjectives have proximal, medial, and distal forms.


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 add meaning of the verb stem (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:

Independent and dependent forms[edit]

Most verbs have, in addition to the tenses, voices, and moods named above, two sets of forms: an independent and a dependent conjugation. The independent conjugation occurs when the verb occurs absolutely sentence-initial with no preverbs, while the dependent conjugation occurs when the verb is preceded by one or more preverbs. The formation of the independent and dependent conjugations depends on whether a verb is simple or complex. A complex verb is a verb that is always combined with a preverb, while all other verbs are simple verbs. The dependent conjugation of a simple verb is essentially the same as the independent conjugation of a complex verb, though different terminology is used:

Independent Dependent
Simple verb Absolute inflection Conjunct inflection
Complex verb Deuterotonic inflection Prototonic inflection

The absolute and conjunct inflections are distinguished primarily by the endings, 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-). The difference between absolute and conjunct endings is thought to reflect an additional particle *-es added to the absolute verbal form.[1] Final -i in the conjunct forms was apparently lost early on (cf. a similar change in Latin).

The difference between deuterotonic and prototonic inflections involves a stress shift. The stress is always placed on the second preverb from the beginning, due to the Celtic version of Wackernagel's law. Consequently, when a preverb is attached to a verb that already has one, the stress shifts one preverb to the left. This stress shift is accompanied by (sometimes radical) changes in the verbal stem and all but the first preverbal particle(s), which merge with the stem, e.g. do⋅berat "they bring/give", as⋅berat "they say" vs. ní-taibret "they do not bring/give", ní-epret "they do not say". In the s-subjunctive, the allomorphy is even more extreme, especially in the third-person singular: 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 (do⋅rósc(a)i "he surpasses" vs. ní-derscaigi "he does not surpass") or even unrecognisable (imm⋅soí "he turns around" vs. ní-impaí "he does not turn around"). However, the forms usually result from a series of regular sound changes.[* 1]


Two main classifications of Old Irish verbs exist, both based on the formation of the present indicative: the Thurneysen classification and the McCone classification. Both systems classify verbs broadly between weak and strong, the distinction being that weak verbs have a 3rd person singular conjunct form ending in a vowel, while strong verbs have a 3rd person singular conjunct form ending in a consonant. This distinction, like the strong-weak distinction found in the Germanic languages, reflects the PIE split between primary and secondary verbs. McCone's system additionally has a separate class for so-called "hiatus" verbs, in which the root itself ends in a vowel rather than the verb having a vocalic suffix, as in the "true" weak verbs. Thurneysen groups these with the weak verbs.

Thurneysen McCone Characteristic Example Origin
A I W1 3rd sg. conj. -a mór(a)id, ·móra "magnify" PC *-ā- < PIE *-eh₂- (cf. Latin -āre)
A II W2a 3rd sg. conj. -i lé(i)cid, ·lé(i)ci "leave" PC *-ī- < PIE denominative *-eyé-
W2b 3rd sg. conj. -i, root vowel o or u roithid, ·roithi "make run" PC *-ī- < PIE causative *-éye-
A III H1 Hiatus verbs: root ending -a raïd/ráïd, ·rá "row" PIE simple thematic verbs (usually of seṭ roots)
H2 Hiatus verbs: root ending -i gniïd/gníïd, ·gní "do"
H3 Hiatus verbs: root ending other vowels sceïd/scéid, ·scé "vomit"
B I S1a Palatalisation in 2rd and 3rd sg, 2nd pl. beirid, ·beir "carry" PIE simple thematic verbs
S1b Palatalisation in 3rd sg conjunct only canaid, ·cain "sing" ?
B II S2 Palatalisation in all forms gaibid, ·gaib "take" PIE thematic verbs in *-ye-
B III S1c n-infix, palatalisation as B I boingid "break", with reduplicated preterite bobag- PIE n-infix verbs
B IV S3a Nonpalatalised n-suffix crenaid "buy", 3rd sing. subjunctive ·cria PIE n-infix verbs to (vowel-final) seṭ roots
B V S3b Alternating broad/slender n-suffix ara·chrin "decay", pl. ara·chrinat PIE -new- ~ -nu-

Old Irish verbs have, however, up to five principal parts, so that for the complete conjugation of a verb all five inflectional stems must be known. These are:

  • Present stem: forms the present and imperfect indicative, and the imperative.
  • Subjunctive stem: forms the present and past subjunctive
  • Future stem: forms the future
  • Preterite active stem: forms the active preterite forms
  • Preterite passive stem: forms the passive preterite forms

Subjunctive stem types[edit]

The subjunctive comes in two variants, both continuing the PIE s-aorist subjunctive.[citation needed]

Type Verb types
a-subjunctive Weak and hiatus verbs, strong verbs with a root ending in any other consonant
s-subjunctive Strong verbs with a root ending in a dental or velar consonant or in -nn

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.[* 2]

Future stem types[edit]

The future comes in four variants.

Type Verb types Remarks
f-future All weak verbs, H3 hiatus verbs Added to present stem; same endings as a-subjunctive, except 1st sg. conjunct.
s-future Verbs that have an s-subjunctive Formed like s-subjunctive, sometimes with additional reduplication. Same endings as s-subjunctive, except 1st sg. absolute.
a-future H1 hiatus verbs, S1 and S2 strong verbs with root ending in b, l, m, n, r, a few other weak or hiatus verbs Same endings as a-subjunctive. Either reduplicated or with é in the root.
i-future H2 and S3 hiatus verbs with root-final i Same endings as W2 present, except 2nd sg. Either reduplicated or with íu in the root.

Preterite active stem types[edit]

The preterite active comes in four variants:

Type Verb types Remarks
s-preterite All weak and hiatus verbs, and gaibid "take", ibid "drink Reduplication in most hiatus verbs.
t-preterite All strong verbs with root ending in l or r, some ending in g, and em- "take", sem- "pour".
Reduplicated preterite Some strong verbs
Long vowel preterite Some strong verbs Originally also reduplicated, but the reduplication was lost and various other changes resulted.

Preterite passive stem types[edit]

The preterite passive occurs only in one type, with a t-suffix, originally to the zero-grade root. It originates in the PIE verbal adjective in *-tós.


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[2] do⋅berid, -ith as⋅berid, -ith *-beretes[2] ní-taibrid, -ith ní-eprid, -ith
3rd Pl ber(a)it *beronti-s do⋅berat as⋅berat *-beront(i) ní-taibret ní-epret


Prepositions inflect for person and number, and different prepositions govern different cases, sometimes depending on the semantics intended.


Old Irish has VSO word order shared by most Insular Celtic languages. Other orders are possible, especially under Bergin's Law. Verbs are all fully conjugated and have most forms typical of Indo-European languages. 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.


  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. ^ 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. ^ Thurneysen 1946, p. 363.
  2. ^ a b Sihler 1995, p. 465.