Old Irish grammar


This article describes the grammar of the Old Irish language.

Grammatical processes

Initial mutations

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 "towards a house" vs. fo thech "under a house", i tech "into a house", with the alternation in the initial consonant of tech "house" triggered by the preceding preposition.
There are three types of mutation:
The mutations became an important part of the grammar and remain, with little change, in Modern Irish. 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":
No changeLenitionNasalizationAspiration/gemination
ech "horse"a ech "his horse"a n-ech "their horse"a ech "her horse"
bo "cow"a bo "his cow"a m-bo "their cow"a bo "her cow"
tech "house"a thech "his house"a tech "their house"a tech "her house"
fer becc "small man" dá fer becc "two small men" fer m-becc "small man"

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

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 above the letter.
Lenition occurs after:
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, 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.
Nasalisation occurs after:
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 to a vowel-initial word. It was primarily caused by syllables formerly ending in, which lenited to between vowels. In gemination, an initial consonant was geminated by a preceding word originally ending in, or after a vowel. By analogy, words originally ending in and 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:
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 "door" originally had a front vowel e in the second syllable, 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 and dative plural doirsib.
Palatalisation can sometimes affect the immediately preceding vowel:
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 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 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. Thus, while the noun cenn was raised to cinn in the genitive singular form, ech was not raised and retained its original vowel in its genitive singular form eich.
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 following u. It involved inserting the vowel u after an existing vowel, and occurred with the long vowel é and the short vowels a, e and i. The results were as follows:
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.

Articles

Old Irish had a definite article but no indefinite article. This meant a noun without an article can refer to either a general reference, or an indefinite reference to a singular occurrence of a noun.

The definite article

The definite article is used similarly to the English one, marking definite noun phrases.
There was also a restriction that prohibited two definite articles in the same noun phrase. When a definite-marked noun is modified by a genitive definite noun phrase, the modified noun loses its article. The definite article can also be used for the introduction of a new character into a narrative, where in English an indefinite article is expected.

Declension of the definite article

The definite article is declined for case, gender, and number, and phonological context.

Morphophonology of the definite article

The declined forms of the article are also influenced by the initial phoneme of the following word.
Accusative and especially dative articles undergo mandatory fusion with a preceding preposition, to the point that the dative article seldom ever appears independently. The dative article suffix lacks -s- if the preposition normally lenites a following noun or is oc. The dative article suffix contains -s- if it fails to lenite a following noun, or is tre. For may or may not take -s-.
Examples of the article fusing with the preposition include:
Old Irish has three 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 dá "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:
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. They are characterized by a genitive singular formed by palatalizing the final consonant of the word. Some monosyllables may have their root vowel e or o raised to i or u respectively when forming the genitive singular. Additionally, their dative singular forms are a constant target for u-infection.
The masculine o-stems' nominative plurals were identical to their genitive singulars and had an accusative plural ending in -u. The accusative plural tended to trigger vowel raising, syncope of multisyllabic words, and occasionally u-infection.
The declensions of fïach "raven" and fíach "debt" demonstrate the contrast between a hiatus of two vowels and a similar-looking diphthong. fíach also demonstrates ía and é alternations, the former appearing in front of unpalatalized consonants and the latter appearing before palatalized consonants.
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. There were two forms of the nominative-accusative plural, an endingless form and a longer form that ended in -a. The endingless form was common after numerals and the definite article, while the long form tended to occur when the noun is used without an article.

io-stems

The io-stems were originally simply o-stems with a 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.

ā-stems

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

iā-stems

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

ī-stems

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.

i-stems

The i-stems could have any gender. This declension class was characterized by the alternation between a nominative singular ending in a slender consonant and the genitive singular depalatalizing that consonant when attaching the signature genitive ending without fail. The genitive singular formation for monosyllables would also lower any root vowel i or u into e and o respectively. The plural forms could either be always palatalised, or never, while in the singular and dual, the palatalisation depended on the ending.
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.
Several irregular vowel alternations within i-stem nouns existed. bíail "axe" demonstrates the opposite of the usual ía/é alternation - ía appears here in front of a slender final consonant while é appeared before a broad consonant. A few other words alternated between a in the nominative singular and e in the genitive singular, such as aig "ice".
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.

u-stems

The u-stems could be masculine or neuter, and their declensions resembled that of i-stems. Like the i-stems, monosyllables would have their nominative singular root vowel lowered from i and u to e and o in the genitive singular form. Feminine u-stem nouns had originally existed, but they had all been converted into ā-stems by the time Old Irish was written. The major difference between u-stems and i-stems were that the nominative singular and its homophones always ended in an unpalatalized consonant, when the opposite was true of the i-stems. None of the endings triggered palatalisation by themselves. However, palatalisation did occur when a syllable containing a front vowel was contracted; the front vowel itself would then be erased by a u-infection in the inflections that did not involve this syncope.
The masculine u-stem nominative plural was often in flux, and attestations varied wildly in its form, with endings in -e, -a, and -i all being attested.
Neuter u-stems were not very common. The genitive and dative forms were the same as in the masculine variety. Like the neuter o-stems, they had two forms for the nominative/accusative plural; one identical with the nominative singular but triggering lenition instead of nasalization, and a form ending in -a. The two forms shared similar usage tendencies as their o-stem counterparts.

Velar stems

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 or c. 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.

Dental stems

The dental stems were also consonant stems, and had a stem ending in a dental consonant, th, d or t. 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.
Only a few neuters existed.

r-stems

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. Later varieties of Irish attached velar-stem endings to the plural of all members of this class. Only bráthair "brother" survived into Modern Irish with its r-stem declension intact.

s-stems

The s-stems were all neuter. 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.

n-stems

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:
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.
The nouns with unlenited -n inflected as follows:
The neuters of this class continued the Indo-European proterokinetic neuters in *-men-. Consequently, they almost all ended in -m in Old Irish.
One neuter r/n-heteroclitic noun existed, arbor "grain".
Singular
Nominativearbor
Vocativearbor
Accusativearbor
GenitivearbaeH
DativearbaimmL

Irregular nouns

Ben "woman" preserved a vestige of Indo-European ablaut, with a zero-grade stem *bn- evolving to mn-. The ablaut allowed several instances of the Proto-Celtic feminine theme long vowel ā to survive into Irish intact in its declension paradigm, since the zero-grade allowed the thematic vowel in those inflections to become tonic syllable nuclei and thus evade several vowel reductions that affected the rest of the ā-stems.
There was one noun, duine, which suppleted its plural forms from another root. Its singular declined like a masculine io-stem while its plural declined like an i-stem. The dual forms of this term are unattested.
Also irregular were a few miscellaneous consonant-stem nouns that were neither velar stems, dental stems, nt-stems, nor n-stems. Three of these nouns retained vestiges of a consonant-stem declension with a stem-final -w- in Proto-Celtic. These three nouns are bó "cow", cnú "nut", and crú "blood". The original -w- had vanished in almost all forms.
Another miscellaneous consonant stem, mí "month", had a root ending in -ns- in Proto-Celtic.

Adjectives

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

Verbs

Verbs stand initially in the sentence. The verb can be either suffixed for tense, person, mood and aspect, or these can be shown by vowel changes in the stem. 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. 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: 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:
IndependentDependent
Simple verbAbsolute inflectionConjunct inflection
Complex verbDeuterotonic inflectionPrototonic 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". The difference between absolute and conjunct endings is thought to reflect an additional particle *-es added to the absolute verbal form. Final -i in the conjunct forms was apparently lost early on.
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 changes in the verbal stem and all but the first preverbal particle, 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 or even unrecognisable. However, the forms usually result from a series of regular sound changes. A few verbs form their prototonic forms irregularly. Two verbs beginning with the prefix ro-, ro·cluinethar and ro·finnadar form their prototonic forms by solely deleting the prefix without any stem change. Two other verbs, fo·ceird and do·bidci use suppletion to create their prototonic forms.

Classification

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.
ThurneysenMcConeCharacteristicExampleOrigin
A IW13rd sg. conj. -amórid, ·móra "magnify"PC *-ā- < PIE *-eh₂-
A IIW2a3rd sg. conj. -ilécid, ·léci "leave"PC *-ī- < PIE denominative *-eyé-
A IIW2b3rd sg. conj. -i, root vowel o or uroithid, ·roithi "make run"PC *-ī- < PIE causative *-éye-
A IIIH1Hiatus verbs: root ending -araïd/ráïd, ·rá "row"PIE simple thematic verbs
A IIIH2Hiatus verbs: root ending -igniïd/gníïd, ·gní "do"PIE simple thematic verbs
A IIIH3Hiatus verbs: root ending other vowelssceïd/scéid, ·scé "vomit"PIE simple thematic verbs
B IS1a & S1bPalatalisation in 2rd and 3rd sg, 2nd pl.beirid, ·beir "carry"PIE simple thematic verbs
B IS1cPalatalisation in 3rd sg conjunct onlycanaid, ·cain "sing"?
B IIS2Palatalisation in all formsgaibid, ·gaib "take"PIE thematic verbs in *-ye-
B IIIS1dn-infix, palatalisation as B Iboingid "break", with reduplicated preterite bobag-PIE n-infix verbs
B IVS3aNonpalatalised n-suffixcrenaid "buy", 3rd sing. subjunctive ·criaPIE n-infix verbs to seṭ roots
B VS3bAlternating broad/slender n-suffixara·chrin "decay", pl. ara·chrinatPIE -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:
Reduplication in Old Irish verbal conjugation tends to happen in the formation of s-futures, a-futures and reduplicated preterites, especially in strong verbs.
However, due to various historical phonetic deletions, the reduplication may not be obvious, and in some cases the reduplication of one verb would be analogically extended to other verbs that did not reduplicate similarly. For example, sligid "strikes down" has a reduplicated preterite selaig "struck down" and an s-future silis "will strike down", with a lost reduplicated s formerly in front of the l in both paradigms.
PresentReduplicated preterites-futureNotesEnglish translation
sligidselaigsiliss lost when reduplicatingstrikes down, fells
lingidleblaingInitial reduplicating Proto-Celtic *ɸ lost, initial l later restored.leaps
·seinn sephainnsibsaProto-Celtic *sw becoming /f/ in preterite, leading to the medial labiodentals in preterite and s-future.plays musical instruments, strikes
orgaidiurait Vowel-initial reduplicationkills
ro·cluinetharro·cúalaero·cechladarIn Proto-Celtic, the preterite reduplicated with *o. Reduplicating *k in the middle of the word was then lost, causing compensatory lengthening. Long o proceeded to break into a diphthong. Future stem demonstrates lowering of reduplicating i to e in front of a.hears
fichidfíchfeisProto-Celtic reduplicating *w was lost intervocally, but remained word-initially as Old Irish f.fights

Augmentation

Old Irish verbs may systematically use certain verbal prefixes to express either perfect aspect or potentiality. Such prefixes are called augments. Perfective augmentation is generally performed on the preterite indicative, creating perfect-aspect forms, while potential augmentation is applied to subjunctive forms. Both augmentations may be done albeit much less commonly on the present indicative, and rarely appear elsewhere.
Augmentation of the preterite marked the later relevance or significance of a past action, and as such often, but not always, corresponds to the perfect aspect. Additionally, augmenting a preterite verb in a subordinate clause indicates the completion of an action in that clause before the action indicated by another non-subordinated preterite phrase, slightly resembling a pluperfect. This sort of augmentation may also accompany another verb in the habitual or gnomic present to describe an action preceding another within an aphorism.
Augmentation of the subjunctive indicates marks the potentiality of an action, and can be used instead of the general potential verb con·icc "can, to be able to". It is also not uncommon for the present indicative to be able to receive potential augments as well. Hence one can say Ní·dérnai "he can't do it" instead of Ní·cumaing a dénum "he can't do it".

Formation of augmented forms

The vast majority of verbs use ro- as their augment. However, there are several major exceptions to using ro-.
Furthermore, some verbs are prohibited from using augments entirely. These verbs include those derived from the roots ·icc and ·gnin, any verbs already lexically containing the ro- prefix, ad·cota "to get", and fo·gaib "to find".

Subjunctive stem types

The subjunctive comes in three variants, all continuing the PIE s-aorist subjunctive.
TypeVerb types
a-subjunctiveWeak and hiatus verbs, strong verbs with a root ending in any other consonant
e-subjunctiveHiatus verbs with a root ending in i
s-subjunctiveStrong 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" <, prototonic ·opind < ; subj. as·bó <, prototonic ·op < ; 2 sg. subj. as·bóis <, prototonic ·obbais < with thematic *-s-es.
In the e-subjunctive, the root-final vowel i of a suitable hiatus verb is transformed into e in the subjunctive and is followed directly by a personal ending with neither -s- nor -a- being additionally suffixed in between.
The below table, comparing the conjugations of the a- and s-subjunctives, uses beirid "to carry" and do·beir "to give, bring" as examples of a-subjunctive formation while téit "to go" and at·reig "to rise" serve as examples of s-subjunctive formations. For e-subjunctive formations, these are sparsely attested outside of the very common verbs at·tá "to be" and do·gní "to do", and go unused in the prototonic forms of compounds, where a-subjunctives are used instead.

Future stem types

The future comes in four variants.
TypeVerb typesRemarks
f-futureAll weak verbs, H3 hiatus verbsAdded to present stem; same endings as a-subjunctive, except 1st sg. conjunct.
s-futureVerbs that have an s-subjunctiveFormed like s-subjunctive, usually with additional reduplication. Same endings as s-subjunctive, except 1st sg. absolute.
a-futureH1 hiatus verbs, S1 and S2 strong verbs with root ending in b, l, m, n, r, a few other weak or hiatus verbsSame endings as a-subjunctive. Either reduplicated or with é in the root.
i-futureH2 and S3 hiatus verbs with root-final iSame endings as W2 present, except 2nd sg. Either reduplicated or with íu in the root.

In the below table, beirid "to carry" and its derivative do·beir "to bring, give" is once again used to demonstrate an a-future conjugation. For s-future formations, cingid "to step" and fo·loing "to support, sustain" are drawn upon.

Preterite active stem types

The preterite active comes in four variants:
TypeVerb typesRemarks
s-preteriteAll weak and hiatus verbs, and gaibid "take", ibid "drinkReduplication in most hiatus verbs.
t-preteriteAll strong verbs with root ending in l or r, some ending in g, and em- "take", sem- "pour".
Reduplicated preteriteSome strong verbs
Long vowel preteriteSome strong verbsOriginally also reduplicated, but the reduplication was lost and various other changes resulted.

The reduplicated and long vowel preterites share a conjugation pattern. No second-person plural absolute forms are attested for any preterite formation, and no non-third-person absolute forms are attested for any t-preterite formations.
The preterite conjugations of léicid "to leave, let" for the absolute s-preterite, orcaid "to slay" for the absolute t-preterite, do·beir "to give, to bring" for the conjunct t-preterite, téit "to go" for the absolute suffixless preterite, and do·icc "to reach" for the conjunct suffixless formation are listed in the below table. In addition, the augmented preterite forms of do·beir "to give" for the conjunct s-preterite and as·beir for an unstressed conjunct t-preterite are also provided.

Preterite passive stem types

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.

Example

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

Prepositions

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

Pronouns

Independent personal pronouns

Independent personal pronouns have been reduced to emphatic and topical function, and only occur in the nominative generally following the copula. The copula remains in its third-person singular forms regardless the person and number of the independent pronoun, with the exception of the third-person plural, which forces the copula into its third-person plural forms.
However, in the modern Goidelic languages they have become much more common, even for non-emphatic purposes.

Infixed personal pronouns

By far the most prolific Old Irish personal pronoun formations are their affixed personal pronouns. These serve as direct object pronouns and are always attached onto the preverb preceding the stressed portion of a deuterotonic verbal complex. If a deuterotonic formation does not exist by default, the preverb no is used with the conjunct forms of the simple verb to concoct deuterotonic forms. For example, the simple verb caraid, conjunct ·cara "loves" can form a deuterotonic base no·cara onto which infixed pronouns can be attached.
The infixed pronouns belong to three classes, conventionally labelled A, B, and C. The three classes vary by the phonological context of the preverb or syntactical context of the clause containing it. They are attached between the first preverb and the next stressed syllable.
Various irregularities in the phonological manifestations of the pronouns exist.
There also existed a set of negative modal pronouns that substitute for the negative imperative particle ná and the negative relative or interrogative particle nád whenever a direct object pronoun was called for. These pronouns were built off a stem nach- or nách-.

Possessive pronouns

Possessive pronouns in Old Irish, as expected, have genitive function. Additionally, when modifying verbal nouns, they may encode the direct object of a transitive verbal noun and the subject of an intransitive verbal noun. Unlike genitive modifiers, they are placed before the modified noun. They do not inflect for case and are immune to any word-initial mutation. However, mo "my" and do "your " lose their in front of a word beginning with a vowel. The initial consonant of do is also devoiced in this situation to and may also be optionally lenited after that to.

Fusion of possessive pronouns with prepositions

Like the definite article, possessive pronouns undergo several compulsory contractions with any preceding prepositions. The fusion is more straightforward, but still has several irregularities.
A much less frequent type of pronominal formation is the suffixed pronoun. Suffixed pronouns also denote direct objects, but are instead exclusive to the third-person singular absolute forms of simple verbs. They cause mandatory syncope of the vowel in front of the voiced dental fricative d that serves as the absolute third-person singular ending, as well as devoicing that consonant termination to th. For example, caraid "she loves" suffixed with the suffixed pronoun -i "him" creates carthai "she loves him", exhibiting the pronouns' signature syncope and devoicing.
There also existed a masculine or neuter suffixed pronoun that can be instead attached to absolute simple verbs' first-person singular future forms in -a, first-person plural forms ending in -mi, and third-person plural forms in -it. This suffixed pronoun took on the form -it. Its vowel suppressed the final vowels of the former two endings and syncopated the vowel of the third.

Syntax

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. Prepositions have the same status as the Latin prepositions, including the property of being verb prefixes.

Relative clauses

in Old Irish are indicated via multiple mutually exclusive strategies. No relative pronouns are used, instead favoring mutations of verbs. The modified noun always precedes the verb beginning its associated relative clause.
A leniting relative clause, with the preceding noun serving as its subject, lenites the initial consonant of a deuterotonic form of a verb, inflected appropriately for person and number. If no such form deuterotonic form already exists, the dummy particle no is used with the simplex's conjunct forms to create the deuterotonic form. For example, Do·ceir in fer could make a relative phrase in fer do·cheir by placing the subject in fer in front of the verb and leniting the initial stressed consonant of the verb do·ceir.
If the object is the antecedent of the relative clause, lenition is not necessary.
Simplex verbs in the third person, first person plural, and in the passive have special relative forms. For instance, from Caraid in fer mo fiair "the man loves my sister" can be made a relative clause In fer caras mo fiair "the man who loves my sister". Unlike the leniting relative construction, the antecedent can always be either the subject or the object of the relative verb, so that there could also be In fer caras mo fiur "the man my sister loves".
Several conjunctions and constructions cause the insertion of a nasal mutation into a following clause. These phenomena are known as nasalizing relative clauses. These clauses occur, non-exhaustively, when:
The nasal mutation for the manifests according to a complex set of rules. Relative forms of simple verbs simply face nasal mutation word-initially. Deuterotonic verbs instead infix the nasal mutation immediately after the first preverb. Class C pronouns go immediately after this nasal infix. Relative forms of the copula, such as bes, go unnasalized but the nasal mutation applies to the following word after the copula instead.

Emphasis

Old Irish does not rely on intonation changes to relay emphasis, unlike English. Instead, a set of particles are suffixed onto words to emphasize a given element of the sentence. The particles, also referred to with the Latin name notae augentes can be attached to verbs and nouns alike. The emphatic suffixes vary by person and number, but contain major syncretism in the third person; the emphatic suffixes for the third person masculine and neuter singular in addition to the third-person plural are identical. The emphatic suffixes are:
On verbs, they can be used to emphasize the subject or object of a verb when they are encoded within its conjugation or infixed pronoun. Their appearance on verbs is governed by an animacy hierarchy, organized in four tiers. The four tiers, from highest to lowest, are first person, second person, third person human, and third-person inanimate. A nota of a lower tier cannot appear if the subject or object of the would-be-affixed verb belongs to a higher tier. A vast majority of notae refer specifically to people. Additionally, for third-person notae, an overtly expressed or relative subject for the verb means that a third-person nota must refer to an object by default.
Hence:
The emphatic particles can also emphasize conjugated prepositions.
They can also emphasize possessive pronouns indirectly by being suffixed after the possessed object, since possessive pronouns go unstressed.
Another strategy for emphasis is to front the emphasized element into a copular clause, and convert the remainder of the sentence into a relative clause. Take for example the basic sentence Marbais fer mo charait "a man killed my friend". Copular emphasis can create:
Genitive and possessive modifiers of verbal nouns exhibit behaviour analogous with that of an ergative–absolutive language. Genitive modifiers indicate the object of a transitive verbal noun, with the transitive subject instead being indicated by a prepositional phrase. On the other hand, intransitive verbs do indeed allow genitive modifiers to indicate their subject.
Preceding the verbal noun by oc "at" and the appropriate conjugation of the verb at·tá "to be" indicates progressive aspect.