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 /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

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

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 coaliscing 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

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
ní and ba

Palatalisation

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 spreaded 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:

é → éu/éo, sometimes íu, as if it had undergone u-insertion.
éu/éo → íu.
ía → é.
áe, óe → aí, oí. 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

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:

a → au.
e → iu if raising can take place, eu/eo otherwise.
i → iu.
é → éu/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.

Nouns

Old Irish had three genders, namely, masculine, feminine and neuter; three numbers, namely, singular, dual and plural; and five cases (nominative, vocative, accusative, genitive and dative). The dual is attested only to a limited degree with somewhat distinct forms, though it is almost always preceded by the cardinal [dá] Error: {{Lang}}: text has italic markup (help) "two", and as such has been retained in the modern Gaelic languages.

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.

o-stems

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	fer^L	fir^L
Vocative	fir^L		firu^H
Accusative	fer^N		firu^H
Genitive	fir^L	fer^L	fer^N
Dative	fiur^L	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	scél^N	scél^N	scél^L, scéla^(L)
Vocative
Accusative
Genitive	scéuil^L	scél^N	scél^N
Dative	scéul^L	scélaib

io-stems

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	céile^H	céile^L	céili^L	daltae^H	daltae^L	daltai^L
Vocative	céili^L		céiliu^H	daltai^L		daltu^H
Accusative	céile^N		céiliu^H	daltae^N		daltu^H
Genitive	céili^L	céile^L	céile^N	daltai^L	daltae^L	daltae^N
Dative	céiliu^L	céilib		daltu^L	daltaib

Neuter io-stems
	Singular	Dual	Plural	Singular	Dual	Plural
Nominative	cride^N	cride^N	cride^L	cumachtae^N	cumachtae^N	cumachtae^L
Vocative
Accusative
Genitive	cridi^L	cride^N	cride^N	cumachtai^L	cumachtae^N	cumachtae^N
Dative	cridiu^L	cridib		cumachtu^L	cumachtaib

ā-stems

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

Feminine ā-stems
	Singular	Dual	Plural
Nominative	túath^L	túaith^L	túatha^H
Vocative	túath^L		túatha^H
Accusative	túaith^N		túatha^H
Genitive	túaithe^H	túath^L	túath^N
Dative	túaith^L	túathaib

iā-stems

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	guide^L	guidi^L	guidi^H	ungae^L	ungai^L	ungai^H
Vocative	guide^L		guidi^H	ungae^L		ungai^H
Accusative	guidi^N		guidi^H	ungai^N		ungai^H
Genitive	guide^H	guide^L	guide^N	ungae^H	ungae^L	ungae^N
Dative	guidi^L	guidib		ungai^L	ungaib

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.

Feminine ī-stems
	Singular	Dual	Plural	Singular	Dual	Plural
Nominative	rígain^L	rígain^L	rígnai^H	aithis^L	aithis^L	aithisi^H
Vocative	rígain^L		rígnai^H	aithis^L		aithisi^H
Accusative	rígnai^N		rígnai^H	aithis^N		aithisi^H
Genitive	rígnae^H	rígnae^L	rígnae^N	aithise^H	aithise^L	aithise^N
Dative	rígain^L, rígnai^L	rígnaib		aithis^L	aithisib

i-stems

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	cnáim^L	cnámai^H	súil^L	súil^L	súili^H
Vocative	cnáim^L		cnámai^H	súil^L		súili^H
Accusative	cnáim^N		cnámai^H	súil^N		súili^H
Genitive	cnámo, -a^H	cnámo, -a^L	cnámae^N	súlo, -a^H	súlo, -a^L	súile^N
Dative	cnáim^L	cnámaib		súil^L	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	muir^N	muir^N	muire^L
Vocative
Accusative
Genitive	moro, -a^H	moro, -a^N	muire^N
Dative	muir^L	muirib

u-stems

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	guth^L	gothae, -ai, -a^H
Vocative	guth		guthu^H
Accusative	guth^N		guthu^H
Genitive	gotho, -a^H	gotho, -a^L	gothae^N
Dative	guth^L	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	dorus^N	dorus^N	dorus^L, doirsea
Vocative
Accusative
Genitive	doirseo, -a^H	doirseo, -a^N	doirse^N
Dative	dorus^L	doirsib

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 (/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	sailig^L	sailig	rí^H	ríg^L	ríg	lie, lia^H	liic^L	lieic, liaic, liic
Vocative	sail		sailchea^H	rí^H		ríga^H	*lie, lia*^H		lecca^H
Accusative	sailig^N		sailchea^H	ríg^N		ríga^H	lieic, liaic, liic^N		lecca^H
Genitive	sailech	sailech^L	sailech^N	ríg	ríg^L	ríg^N	liac(c)	*lieic, liaic, liic^L	liac(c)^N
Dative	sailig^L, sail^L	sailchib		ríg^L, rí^L	rígaib		lieic, liaic, liic^L	*lecaib

Dental stems

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, -th^L	cingid, -th	arae^H	araid^L	araid	carae^H	carait^L	carait
Vocative	cing		cingthea^H	arae^H		arada^H, aradu^H	carae^H		cairtea, -dea^H
Accusative	cingid, -th^N		cingthea^H	araid^N		arada^H, aradu^H	carait^N		cairtea, -dea^H
Genitive	cinged, -th	cinged, -th^L	cinged, -th^N	arad	arad^L	arad^N	carat	carat^L	carat^N
Dative	cingid, -th^L, cing^L	cingthib		araid^L, arae^L	aradaib		carait^L	cairtib, -dib

Only a few neuters existed.

Neuter dental stems
	Singular	Dual	Plural
Nominative	dét^N	dét^N	dét^L
Vocative
Accusative
Genitive	dét	?	dét^N
Dative	déit^L	détaib

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.

Masculine/feminine r-stems
	Singular	Dual	Plural	Singular	Dual	Plural
Nominative	máthair	*máthair^L	máithir	siur	sieir^L	seithir
Vocative	máthair		máithrea^H	siur		sethra^H
Accusative	máthair^N		máithrea^H	sieir^N, siair^N		sethra^H
Genitive	máthar	*máthar^L	máithre^N, máthrae^N	sethar	*sethar^L	sethar^N
Dative	máthair^L	máithrib, máthraib		sieir^L, siair^L	sethraib

s-stems

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	nem^N	nem^N	nime^L	teg^N, tech^N	teg^N, tech^N	tige^L, taige^L
Vocative
Accusative
Genitive	nime^H	nime^L	nime^N	tige^H, taige^H	tige^L, taige^L	tige^N, taige^N
Dative	nim^L	nimib		tig^L, taig^L	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	mí^H	mí^L	mís
Vocative	*mí^H		mísa^H
Accusative	mís^N		mísa^H
Genitive	mís	mí^L	mís^N
Dative	mís^L, mí^L	mísaib

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:

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	talmain^L	talmain	toimtiu^H	toimtin^L	toimtin
Vocative	talam		talmana^H	toimtiu^H		toimtena^H
Accusative	talmain^N		talmana^H	toimtin^N		toimtena^H
Genitive	talman	talman^L	talman^N	toimten	toimten^L	toimten^N
Dative	talmain^L, talam^L	talmanaib		toimte^L, toimtiu^L, toimtin^L	toimtenaib

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

Masculine/feminine n-stems, unlenited
	Singular	Dual	Plural
Nominative	gobae^H	gobainn^L	gobainn
Vocative	gobae^H		goibnea^H
Accusative	gobainn^N		goibnea^H
Genitive	gobann	gobann^L	gobann^N
Dative	gobainn^L, gobae^L	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	céimm^N	céimm^N	céimmenn^L	ainm^N	ainm^N	anmann^L
Vocative
Accusative
Genitive	céimme^H	?	céimmenn^N	anmae^H	?	anmann^N
Dative	céimmimm^L, céimm^L	céimmennaib		anmaimm^L, ainm^L	anmannaib

Irregular nouns

Adjectives

Verbs

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-] Error: {{Lang}}: text has italic markup (help), [ex-] Error: {{Lang}}: text has italic markup (help), [in-] Error: {{Lang}}: text has italic markup (help), [dē-] Error: {{Lang}}: text has italic markup (help), 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] Error: {{Lang}}: text has italic markup (help) and [-se] Error: {{Lang}}: text has italic markup (help) 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:

extensive ablaut variations, made significantly more complicated by vowel affection and syncope
reduplication
primary and secondary endings
thematic and athematic endings
deponent verbs
multiple ways of forming each of the various tenses and moods, and no general cross-tense/mood conjugational classes, i.e. in general a series of principal parts must be memorised for each verb, much as in Latin or Ancient Greek.
n-infix verbs

Independent and dependent forms

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 accopanied 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]}

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.

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-
A II	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
B I	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

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

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

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

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 (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
	Absolute		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

Syntax

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.

Notes

^ 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.
^ 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").

References

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

[2] 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.

[3] 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").

[FOOTNOTEThurneysen1946363-1] Thurneysen 1946, p. 363.

[FOOTNOTESihler1995465-4] Sihler 1995, p. 465.

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