Proto-Celtic language
Proto-Celtic, or Common Celtic, is the reconstructed ancestral proto-language of all known Celtic languages, and a descendant of Proto-Indo-European. It is not attested in writing but has been partly reconstructed through the comparative method. Proto-Celtic is generally thought to have been spoken between 1300 and 800 BC, after which it began to split into different languages. Proto-Celtic is often associated with the Urnfield culture and particularly with the Hallstatt culture. Celtic languages share common features with Italic languages that are not found in other branches of Indo-European, suggesting the possibility of an earlier Italo-Celtic linguistic unity.
Proto-Celtic is currently being reconstructed through the comparative method by relying on later Celtic languages. Though Continental Celtic presents much substantiation for Proto-Celtic phonology, and some for its morphology, recorded material is too scanty to allow a secure reconstruction of syntax, though some complete sentences are recorded in the Continental Gaulish and Celtiberian. So, the main sources for reconstruction come from Insular Celtic languages with the oldest literature found in Old Irish and Middle Welsh, dating back to authors flourishing in the 6th century AD.
Dating
Proto-Celtic is usually dated to the Late Bronze Age, ca. 1200–900 BC. The fact that it is possible to reconstruct a Proto-Celtic word for 'iron' has long been taken as an indication that the divergence into individual Celtic languages did not start until the Iron Age ; otherwise, descendant languages might have developed their own, unrelated words for the metal. However, Schumacher and Schrijver suggest a date for Proto-Celtic as early as the 13th century BC, the time of the Canegrate culture, in northwest Italy, and the Urnfield culture in Central Europe, implying that the divergence may have already started in the Bronze Age.Sound changes from Proto-Indo-European
The phonological changes from Proto-Indo-European to Proto-Celtic may be summarized as follows. The changes are roughly in chronological order, with changes that operate on the outcome of earlier ones appearing later in the list.Late PIE
These changes are shared by several other Indo-European branches.- *e is colored by an adjacent laryngeal consonant:
- * eh₂, h₂e > ah₂, h₂a
- * eh₃, h₃e > oh₃, h₃o
- Palatovelars merge into the plain velars:
- * ḱ > k
- * ǵ > g
- * ǵʰ > gʰ
- Epenthetic *a is inserted after a syllabic sonorant if a laryngeal and another sonorant follow
- Laryngeals are lost:
- * before a following vowel
- * following a vowel in syllables before the accent
- * following a vowel before a consonant, or word finally, resulting in compensatory lengthening, thus
- * between plosives in non-initial syllables
- Two adjacent dentals become two adjacent sibilants
Italo-Celtic
The following sound changes are shared with the Italic languages in particular, and are cited in support of the Italo-Celtic hypothesis.- Dybo's rule: long close vowels are shortened before resonant + stressed vowel. Note that something like Dybo's rule seems to have also operated in Germanic.
- * īR´ / ? *iHR´ > iR´
- * ūR´ / ? *uHR´ > uR´
- Possibly, post-consonantal laryngeals are lost when before pre-tonic close vowels:
- * CHiC´ > CiC´
- * CHuC´ > CuC´
- Development of initial stress, following the previous two changes. But note that this seems to have been an areal feature, shared, for example with the Indo-European Germanic languages and the non-Indo-European Etruscan language.
- Possibly, vocalization of laryngeals to *ī between a *CR cluster and consonantal *j
- Syllabic laryngeals become *a
- Syllabic resonants before a voiced unaspirated stop become *Ra
- *m is assimilated or lost before a glide:
- * mj > nj
- * mw > w
- *p assimilates to *kʷ when another *kʷ follows later in the word this change may have occurred late in Celtic; B) it seems not to have operated on some words in Irish; and C) a similar assimilation also occurred in Germanic.
- Word-initially, HR̩C > aRC
- Before voiceless stops, CR̩HT > CRaT
- CR̩HV > CaRHV
- CR̩HC > CRāC
Early PC
- Sequences of velar and *w merge into the labiovelars :
- * kw > kʷ
- * gw > gʷ
- * gʰw > gʷʰ
- *gʷ merges into *b.
- Aspirated stops lose their aspiration and merge with the voiced stops :
- * bʰ > b
- * dʰ > d
- * gʰ > g
- * gʷʰ > gʷ
- *e before a resonant and *a becomes *a as well : *ǵʰelH-ro > *gelaro > *galaro / *gérH-no > *gerano > *garano.
- Epenthetic *i is inserted after syllabic liquids when followed by a plosive:
- * l̩T > liT
- * r̩T > riT
- Epenthetic *a is inserted before the remaining syllabic resonants:
- * m̩ > am
- * n̩ > an
- * l̩ > al
- * r̩ > ar
- All remaining nonsyllabic laryngeals are lost.
- ē > ī
- ō > ū in final syllables
- Long vowels are shortened before a syllable-final resonant ; this also shortens long diphthongs.
Late PC
- Plosives become *x before a different plosive or *s
- p > b before liquids
- p > w before nasals
- p > ɸ
- ō > ā
- ey > ē
- ew > ow
- uwa > owa
Phonological reconstruction
Consonants
The following consonants have been reconstructed for Proto-Celtic :Allophones of plosives
Eska has recently proposed that PC stops allophonically manifest similarly to those in English. Voiceless stop phonemes were aspirated word-initially except when preceded by, hence aspirate allophones ; unaspirated voiced stops were devoiced to word-initially.This allophony may be reconstructed to PC from the following evidence:
- Modern Celtic languages like Welsh, Breton, and all modern Goidelic languages have such plosive aspiration and voice allophony already attested.
- Several old Celtic languages used letters for voiceless stop phonemes to write both voiceless stop phonemes and their voiced counterparts, especially non-word-initially.
- The Celtiberian Luzaga's Bronze has the curious spelling of an accusative determiner sdam, where the d is clearly meant to spell. This implies that Celtiberian had a voiceless allophone.
Evolution of plosives
Proto-Indo-European voiced aspirate stops *bʰ, *dʰ, *gʰ/ǵʰ, merge with *b, *d, *g/ǵ in PC. The voiced aspirate labiovelar *gʷʰ did not merge with *gʷ, though: plain *gʷ became PC *b, while aspirated *gʷʰ became *gʷ. Thus, PIE gʷen- 'woman' became Old Irish and Old Welsh ben, but PIE gʷʰn̥- 'to kill, wound' became Old Irish gonaid and Welsh gwanu.PIE *p is lost in PC, apparently going through the stages *ɸ and *h before being completely lost word-initially and between vowels. Next to consonants, PC *ɸ underwent different changes: the clusters *ɸs and *ɸt became *xs and *xt respectively already in PC. PIE *sp- became Old Irish s and Brythonic f; while argues there was an intermediate stage *sɸ-, finds it more economical to believe that *sp- remained unchanged in PC, that is, the change *p to *ɸ did not happen when *s preceded.
In Gaulish and the Brittonic languages, the Proto-Indo-European kʷ phoneme becomes a new p sound. Thus, Gaulish petuar, Welsh pedwar "four", but Old Irish cethair and Latin quattuor. Insofar as this new fills the gap in the phoneme inventory which was left by the disappearance of the equivalent stop in PIE, we may think of this as a chain shift.
The terms P-Celtic and Q-Celtic are useful for grouping Celtic languages based on the way they handle this one phoneme. But a simple division into P- / Q-Celtic may be untenable, as it does not do justice to the evidence of the ancient Continental Celtic languages. The unusual shared innovations among the Insular Celtic languages are often also presented as evidence against a P- vs Q-Celtic division, but they may instead reflect a common substratum influence from the pre-Celtic languages of Britain and Ireland,, or simply continuing contact between the insular languages; in either case they would be irrelevant to the genetic classification of Celtic languages.
Q-Celtic languages may also have in loan words, though in early borrowings from Welsh into Primitive Irish, was used by sound substitution due to a lack of a phoneme at the time:
- Latin Patricius "Saint Patrick"' > Welsh > Primitive Irish > Old Irish Cothrige, later Pádraig;
- Latin presbyter "priest" > early form of word seen in Old Welsh premter primter > Primitive Irish > Old Irish cruimther.
Vowels
The PC vowel system is highly comparable to that reconstructed for PIE by Antoine Meillet. The following monophthongs are reconstructed:The following diphthongs have also been reconstructed:
Morphology
Nouns
The morphological structure of nouns and adjectives demonstrates no arresting alterations from the parent language. Proto-Celtic is believed to have had nouns in three genders, three numbers and five to eight cases. The genders were masculine, feminine and neuter; the numbers were singular, plural and dual. The number of cases is a subject of contention: while Old Irish may have only five, the evidence from Continental Celtic is considered rather unambiguous despite appeals to archaic retentions or morphological leveling. These cases were nominative, vocative, accusative, dative, genitive, ablative, locative and instrumental.Nouns fall into nine or so declensions, depending on stem. There are *o-stems, *ā-stems, *i-stems, *u-stems, dental stems, velar stems, nasal stems, *r-stems and *s-stems.
*''o''-stem nouns
makkʷos 'son'| Case | Singular | Dual | Plural |
| Nominative | *makkʷos | *makkʷou | *makkʷoi |
| Vocative | *makkʷe | *makkʷou | *makkʷūs |
| Accusative | *makkʷom | *makkʷou | *makkʷūs |
| Genitive | *makkʷī | *makkʷūs | *makkʷom |
| Dative | *makkʷūi | *makkʷobom | *makkʷobos |
| Ablative | *makkʷū | *makkʷobim | *makkʷobis |
| Instrumental | *makkʷū | *makkʷobim | *makkʷūs |
| Locative | *makkʷei | *makkʷou | *makkʷobis |
However, Celtiberian shows -o- stem genitives ending in -o rather than -ī: aualo " of Avalos". Also note that the genitive singular does not match Proto-Indo-European's -osyo, which would have yielded -osjo.
- dūnom 'stronghold'
| Case | Singular | Dual | Plural |
| Nominative | *dūnom | *dūnou | *dūnā |
| Vocative | *dūnom | *dūnou | *dūnā |
| Accusative | *dūnom | *dūnou | *dūnā |
| Genitive | *dūnī | *dūnūs | *dūnom |
| Dative | *dūnūi | *dūnobom | *dūnobos |
| Ablative | *dūnū | *dūnobim | *dūnobis |
| Instrumental | *dūnū | *dūnobim | *dūnūs |
| Locative | *dūnei | *dūnou | *dūnobis |
As in the masculine paradigm, the genitive singular does not match Proto-Indo-European's -osyo, which would have yielded -osjo.
*''ā''-stem nouns
E.g. ɸlāmā 'hand' (Old Irish lám; Welsh llaw\\*''i''-stems
E.g. sūlis 'sight, view, eye'| Case | Singular | Dual | Plural |
| Nominative | *sūlis | *sūlī | *sūlīs |
| Vocative | *sūli | *sūlī | *sūlīs |
| Accusative | *sūlim | *sūlī | *sūlīs |
| Genitive | *sūleis | *sūljous | *sūljom |
| Dative | *sūlei | *sūlibom | *sūlibos |
| Ablative | *sūlī | *sūlibim | *sūlibis |
| Instrumental | *sūlī | *sūlibim | *sūlibis |
| Locative | *sūlī | *sūlibim | *sūlibis |
E.g. mori 'body of water, sea'
| Case | Singular | Dual | Plural |
| Nominative | *mori | *morī | *moryā |
| Vocative | *mori | *morī | *moryā |
| Accusative | *mori | *morī | *moryā |
| Genitive | *moreis | *moryous | *moryom |
| Dative | *morei | *moribom | *moribos |
| Ablative | *morī | *moribim | *moribis |
| Instrumental | *morī | *moribim | *moribis |
| Locative | *morī | *moribim | *moribis |
*''u''-stem nouns
E.g. bitus 'world, existence'| Case | Singular | Dual | Plural |
| Nominative | *bitus | *bitou | *bitowes |
| Vocative | *bitu | *bitou | *bitowes |
| Accusative | *bitum | *bitou | *bitūs |
| Genitive | *bitous | *bitowou | *bitowom |
| Dative | *bitou | *bitubom | *bitubos |
| Ablative | *bitū | *bitubim | *bitubis |
| Instrumental | *bitū | *bitubim | *bitubis |
| Locative | *bitū | *bitubim | *bitubis |
E.g. *beru "rotisserie spit"
| Case | Singular | Dual | Plural |
| Nominative | *beru | *berou | *berwā |
| Vocative | *beru | *berou | *berwā |
| Accusative | *beru | *berou | *berwā |
| Genitive | *berous | *berowou | *berowom |
| Dative | *berou | *berubom | *berubos |
| Ablative | *berū | *berubim | *berubis |
| Instrumental | *berū | *berubim | *berubis |
| Locative | *berū | *berubim | *berubis |
Velar and dental stems
Before the *-s of the nominative singular, a velar consonant was fricated to *-x : *rīg- "king" > *rīxs. Likewise, final *-d devoiced to *-t-: *druwid- "druid" > *druwits.E.g. "king"
| Case | Singular | Dual | Plural |
| Nominative | *rīxs | *rīge | *rīges |
| Vocative | *rīxs | *rīge | *rīges |
| Accusative | *rīgam | *rīge | *rīgās |
| Genitive | *rīgos | *rīgou | *rīgom |
| Dative | *rīgei | *rīgobom | *rīgobos |
| Ablative | *rīgī | *rīgobim | *rīgobis |
| Instrumental | *rīge | *rīgobim | *rīgobis |
| Locative | *rīgi | *rīgobim | *rīgobis |
E.g. "druid"
| Case | Singular | Dual | Plural |
| Nominative | *druwits | *druwide | *druwides |
| Vocative | *druwits | *druwide | *druwides |
| Accusative | *druwidem | *druwide | *druwidās |
| Genitive | *druwidos | *druwidou | *druwidom |
| Dative | *druwidei | *druwidobom | *druwidobos |
| Ablative | *druwidī | *druwidobim | *druwidobis |
| Instrumental | *druwide | *druwidobim | *druwidobis |
| Locative | *druwidi | *druwidobim | *druwidobis |
E.g. "friend"
| Case | Singular | Dual | Plural |
| Nominative | *karants | *karante | *karantes |
| Vocative | *karants | *karante | *karantes |
| Accusative | *karantam | *karante | *karantās |
| Genitive | *karantos | *karantou | *karantom |
| Dative | *karantei | *karantobom | *karantobos |
| Ablative | *karantī | *karantobim | *karantobis |
| Instrumental | *karante | *karantobim | *karantobis |
| Locative | *karanti | *karantobim | *karantobis |
Nasal stems
Generally, nasal stems end in *-on-; this becomes *-ū in the nominative singular: *abon- "river" > *abū.E.g. "river"
| Case | Singular | Dual | Plural |
| Nominative | *abū | *abone | *abones |
| Vocative | *abū | *abone | *abones |
| Accusative | *abonam | *abone | *abonās |
| Genitive | *abonos | *abonou | *abonom |
| Dative | *abonei | *abnobom | *abnobos |
| Ablative | *abonī | *abnobim | *abnobis |
| Instrumental | *abone | *abnobim | *abnobis |
| Locative | *aboni | *abnobim | *abnobis |
E.g. "name"
| Case | Singular | Dual | Plural |
| Nominative | *anman | *anmanī | *anmanā |
| Vocative | *anman | *anmanī | *anmanā |
| Accusative | *anman | *anmanī | *anmanā |
| Genitive | *anmēs | *anmanou | *anmanom |
| Dative | *anmanei | *anmambom | *anmambos |
| Ablative | *anmanī | *anmambim | *anmambis |
| Instrumental | *anmane | *anmambim | *anmambis |
| Locative | *anmani | *anmambim | *anmambis |
*''s''-stem nouns
Generally,*s-stems contain an *-es-, which becomes *-os in the nominative singular: *teges- 'house' > *tegos.E.g. "house"
| Case | Singular | Dual | Plural |
| Nominative | *tegos | *tegese | *tegesa |
| Vocative | *tegos | *tegese | *tegesa |
| Accusative | *tegos | *tegese | *tegesa |
| Genitive | *tegesos | *tegesou | *tegesom |
| Dative | *tegesi | *tegesobom | *tegesobos |
| Ablative | *tegesī | *tegesobim | *tegesobis |
| Instrumental | *tegese | *tegesobim | *tegesobis |
| Locative | *tegesi | *tegesobim | *tegesobis |
*''r''-stem nouns
- r-stems are rare and principally confined to names of relatives. Typically they end in *-ter-, which becomes *-tīr in the nominative and *-tr- in all other cases aside from the accusative: *ɸater- 'father' > *ɸatīr, *ɸatros.
| Case | Singular | Dual | Plural |
| Nominative | *ɸatīr | *ɸatere | *ɸateres |
| Vocative | *ɸatīr | *ɸatere | *ɸateres |
| Accusative | *ɸateram | *ɸatere | *ɸaterās |
| Genitive | *ɸatros | *ɸatrou | *ɸatrom |
| Dative | *ɸatrei | *ɸatrebom | *ɸatrebos |
| Ablative | *ɸatrī | *ɸatrebim | *ɸatrebis |
| Instrumental | *ɸatre | *ɸatrebim | *ɸatrebis |
| Locative | *ɸatri | *ɸatrebim | *ɸatrebis |
E.g. *mātīr 'mother'
| Case | Singular | Dual | Plural |
| Nominative | *mātīr | *mātere | *māteres |
| Vocative | *mātīr | *mātere | *māteres |
| Accusative | *māteram | *mātere | *māterās |
| Genitive | *mātros | *mātrou | *mātrom |
| Dative | *mātrei | *mātrebom | *mātrebos |
| Ablative | *mātrī | *mātrebim | *mātrebis |
| Instrumental | *mātre | *mātrebim | *mātrebis |
| Locative | *mātri | *mātrebim | *mātrebis |
Pronouns
The following personal pronouns in Celtic can be reconstructed as follows:The following third-person pronouns in Proto-Celtic may also be reconstructed.
Forms of the masculine singular relative pronoun *yo- can be found in the first Botorrita plaque: The form io-s in line 10 is the nominative singular masculine of the relative pronoun from Proto-Indo-European *yo-, which shows up in Old Irish only as the aspiration for leniting relative verb forms. Line 7 has the accusative singular io-m and the dative singular io-mui of the same root.
Adjectives
Adjectives in Proto-Celtic had positive, comparative, superlative and equative degrees of comparison.Positive-degree inflection classes
Four inflection classes for positive-degree adjectives are known. Most adjectives belonged to the o-ā class, in which the adjectives inflected like masculine o-stems, neuter o-stems and feminine ā-stems when agreeing with nouns of their respective genders. A much smaller minority of adjectives were i- and u-stems.Consonant-stem adjectives also existed but were vanishingly rare, with only relics in Old Irish like té "hot" < *teɸents.
Comparative degree
The comparative degree was formed on most adjectives by attaching *-yūs to the adjective stem. For instance, *senos "old" would have a comparative *senyūs "older". However, some Caland system adjectives instead had a comparative ending in *-is, which was then extended to *-ais. For example, *ɸlitanos "wide" had a comparative *ɸletais.Superlative degree
The superlative was formed by simply attaching *-isamos to the adjective stem. In some adjectives where the stem ends in *s, the suffix is truncated to *-amos by haplology. Thus, *senos "old" would have a superlative *senisamos "oldest" but *trexsnos would have a superlative *trexsamos.Verbs
From comparison between early Old Irish and Gaulish forms it seems that Continental and Insular Celtic verbs developed differently and so the study of Irish and Welsh may have unduly weighted past opinion of Proto-Celtic verb morphology. It can be inferred from Gaulish and Celtiberian as well as Insular Celtic that the Proto-Celtic verb had at least three moods:- indicative — seen in e.g. 1st Gaulish delgu "I hold", Old Irish tongu "I swear"
- imperative — seen in e.g. 3rd Celtiberian usabituz, Gaulish appisetu
- subjunctive — seen in e.g. 3rd Gaulish buetid "may he be", Celtiberian asekati
- present — seen in e.g. Gaulish uediíu-mi "I pray", Celtiberian zizonti "they sow"
- preterite — seen in e.g. 3rd Gaulish sioxti, Lepontic KariTe
- imperfect — perhaps in Celtiberian kombalkez, atibion
- future — seen in e.g. 3rd Gaulish bissiet, Old Irish bieid "he shall be"
Verbs were formed by adding suffixes to a verbal stem. The stem might be thematic or athematic, an open or a closed syllable.
Primary endings
The primary endings in Proto-Celtic were as follows. They were used to form the present, future, and subjunctive conjugations.Present-stem formations
Proto-Celtic possessed a diverse set of ways to form present stems. They can be roughly be divided into two broad categories of athematic and thematic.- Thematic verbs feature a connecting vowel between the present stem and the basic primary endings. This vowel is -o- in the first-person and third-person plural and -e- in the third-person singular and second-person forms. The first-person singular of these verbs end in *-ū.
- Athematic verbs feature no such connecting vowel, and their 1st-person singular forms end in *-mi instead of *-ū.
| Inflectional class | Root ablaut | Affix | Class | KPV designation |
| Thematic | e-grade | Simple thematic | A-1 | |
| Thematic | e-grade | *-ye- | e-grade *-ye- | A-5 |
| Thematic | e-grade | *-de- | e-grade *-de- | A-6 |
| Thematic | o-grade | -ī- -eyo- | *-eye- causative/iterative | |
| Thematic | zero grade | Thematized root athematic | A-2 | |
| Thematic | zero grade | tudáti-type thematic | A-2 | |
| Thematic | zero grade | *-ske- | *-ske- inchoative | A-3 |
| Thematic | zero grade | *-ye- | zero-grade *-ye- | A-4 |
| Thematic | zero grade | Nasal infix | Aniṭ-root nasal-infix | A-8 |
| Thematic | zero grade | i-reduplication | i-reduplicated present | A-15 |
| Thematic | *-āye- | Denominative | ||
| Athematic | e-grade | CeRH-root present | A-13 | |
| Athematic | zero grade | *-na- | seṭ-root nasal-infix | A-8 |
| Athematic | zero grade | *-nu- | *-new- present | A-10 |
| Athematic | zero grade | *-ī- | essive | A-7 |
| Athematic | *-ā- | factitive |
Nasal-infix presents
In Proto-Celtic, the Indo-European nasal infix presents split into two categories: ones originally derived from laryngeal-final roots, and ones that were not. In seṭ verbs, the nasal appears at the end of the present stem, while in aniṭ-derived verbs the nasal was followed by a root-final stop.To ''aniṭ'' roots
Aniṭ nasal infix verbs conjugated exactly like basic thematic verbs in the present tense.However, the origin of the invariant root vowel in -o- in *CewC- roots in Old Irish is unclear. Usually, it is held that the consonantism in these verbs was generalized in favour of the plural stem *CunC- in Old Irish. One would expect alternation between o in the 1st- and 3rd- person plural and -u- elsewhere in the present; but for both contexts Old Irish only attests -o-.
The following verbs can be reconstructed in this class:
- To *CeyC- roots:,,,
- Double-nasal presents:,,
- To *CewC- roots:,,,,,,,,
- Others:,
To ''seṭ'' roots
The seṭ nasal-infix presents were further subdivided into subcategories based on the root-final laryngeal. Traditionally two subclasses have long been accepted, the h₁ subclass and h₂. h₃ nasal-infixed verbs were often leveled to act like h₂ verbs, being also cited with a -na- suffix; the only original difference between the two would have been the 3rd-person plural ending in *-nonti instead of *-nanti.
The nasal-infix seṭ verbs in Proto-Celtic underwent multiple levelings. First, the suffixal vowel in the plural forms was harmonized so that they would all be the short counterpart to the vowel in the singular forms. Then all the long vowels in the singular were shortened to make the suffix vowel identical in quality and length across all person-number combinations.
The following seṭ-root nasal presents are reconstructible for Proto-Celtic:*h₁-final roots:
- * -ni- relics:,,
- * Converted to -na- before Old Irish:,, *h₂ subclass:,,,,,,,, *h₃-final roots:,,
- Semivowel-final aniṭ root:,
- Unknown laryngeal:,,,
Preterite formations
There were two or three major preterite formations in Proto-Celtic, plus another moribund type.- The s-preterite
- The reduplicated suffixless preterite
- The t-preterite
- The root aorist
t-preterite
The Old Irish t-preterite was traditionally assumed to be a divergent evolution from the s-preterite, but that derivation was challenged by Jay Jasanoff, who alleges that they were instead imperfects of Narten presents. Either derivation requires Narten ablaut anyway, leading to a stem vowel i in the singular and e in the plural. The stem vowel in the t-preterite was leveled to *e if the next consonant was either velar or *m, and *i in front of *r or *l.Suffixless preterites
A number of suffixless preterite formations featured reduplication. The nature of the reduplication depends on the structure of the root.| Root | Meaning | Shape | Preterite stem | Notes |
| *keng- | "to step" | Other root types | *ke-kong- | Classic Indo-European reduplication, where the root is put in the o-grade and the prefixed reduplicant is formed with the first consonant followed by *e. |
| *nigʷ- | "to wash" | *CeiT- | *ni-noig- | In Proto-Celtic, roots with a semivowel before a non-laryngeal consonant have the reduplicant formed not with the first consonant of the root followed by *e, but instead the first consonant of the root followed by the semivowel. The root itself remains in the o-grade. |
| *duk- | "to lead, carry" | *CeuT- | *du-douk- | In Proto-Celtic, roots with a semivowel before a non-laryngeal consonant have the reduplicant formed not with the first consonant of the root followed by *e, but instead the first consonant of the root followed by the semivowel. The root itself remains in the o-grade. |
| *gʷed- | "to pray" | *CeT- | *gʷād- | Roots ending in only a single stop as their coda generally merely change the stem vowel to *ā to form their preterite, without apparent reduplication. It originally spread from ād-, the preterite stem for *ed- "to eat". |
| *kerd- | "to throw, put" | *CeRT- | *kard- | A few roots in *CeRT- also had the *CeT- preterite formation applied to them but the long *ā was shortened due to Osthoff's law. |
| *dā- | "to give" | *CeH- | *de-dū *ded- | Laryngeal-final roots produced long vowels in the root syllable in the singular, but not in the plural. Usually the singular stem was generalized in Celtic, but in these cases the plural stem was generalized. |
| *kʷri- | "to buy" | *CeiH- | *kʷi-kʷr- | The treatment for *CeH- roots was also extended to *CeiH- roots. Due to the roots' semivowel, the reduplicant also contains the semivowel. |
Future formations
One major formation of the future in Celtic, the s-future, is possibly a descendant of the Proto-Indo-European se-desiderative, with i-reduplication in multiple verbs. The Old Irish a- and s-future may derive from this same Proto-Indo-European paradigm. According to the philologist Calvin Watkins, certain Old Irish s-future forms may have emerged from a type of Proto-Indo-European desiderative class in which the initial consonant was reduplicated with an intervening i-vowel followed by a sigmatic suffix with the accent placed on the thematic vowel. For instance, Watkins reconstructs a pre-form gʷʰigʷʰr̥- as the ancestor of the Old Irish future form. The linguists Eugen Hill and Jay Jasanoff compare this formation to the reduplicated desiderative of Indo-Iranian and reconstruct an originally thematic paradigm. Hill, in particular, cites the Old Irish term rigid, for which he reconstructs a Proto-Celtic form ri-rix-sū, itself perhaps—according to Hill—from pre-Proto-Celtic *ri-riǵ-sō. The linguist Frederick Kortlandt further proposes that the reduplicated future of Old Irish may parallel several reduplicated forms in Italic, such as Oscan fifikus. However, the Kortlandt alternatively suggests that the s-future and s-subjunctive ultimately derive from the Proto-Indo-European sigmatic aorist and reflect an athematic paradigm. Kortlandt argues that this older athematic inflection was then replaced by secondary thematic endings. Thus, Kortlandt derives Old Irish future forms such as fessa from wiweksom and from gʷedses. Moreover, Kortlandt notes the existence of a full-grade Old Irish future form and a zero-grade form, which may parallel Sanskrit and respectively. According to Kortlandt, the recessive accent of both forms and the full-grade of the former indicate an originally athematic inflection. Jasanoff argues that whereas the Old Irish reduplicated future derives from a thematic source, the unreduplicated s-future is etymologically connected to the Sabellic athematic future, both of which—according to Jasanoff—hold athematic origins. Another future formation, attested only in Gaulish, is the -sye-desiderative.Subjunctive formations
Most verbs took one subjunctive suffix in Proto-Celtic, -s-, followed by the thematic primary endings. The subjunctive in Proto-Celtic was a descendant of the subjunctive of an Indo-European sigmatic formation. The -ase- variant originated in roots that ended in a laryngeal in Proto-Indo-European; when the *-se- suffix was attached right after a laryngeal, the laryngeal regularly vocalized into *-a-. It would then analogically spread to other Celtic strong verb roots ending in sonorants in addition to the weak verbs, even if the root did not originally end in a laryngeal.There were also two, possibly three verbs that did not use -se-, instead straight-out taking thematised primary endings. They are: *bwiyeti "to be, exist", *klinutor "to hear", and possibly *ɸalnati “to approach, drive”.
Primary subjunctive formations in Proto-Celtic generally use the e-grade of the verb root, even if the present stem uses the zero-grade.
Imperative formation
Imperative endings in Proto-Celtic were as follows:Second-person singular imperative
The second-person singular imperative was generally endingless in the active; no ending was generally added to athematic verbs. On thematic -e/o- verbs, the imperative ended in thematic vowel *-e. However, there is also another second-person singular active imperative ending, -si, which was attached to the verb root athematically even with thematic strong verbs.The thematic deponent second-person singular imperative ending was *-eso. The -the in Old Irish is secondary.
Third-person imperative
The third-person imperative endings in Insular Celtic, Gaulish and Celtiberian have completely separate origins from each other. The Insular Celtic endings are derived from *-tou, *-ntou, Gaulish endings from *-tu, *-ntu, and the Celtiberian third-person imperative singular ending stems from *-tūd.Example conjugations
Scholarly reconstructions may be summarised in tabular format.Copula
The copula *esti was irregular. It had both athematic and thematic conjugations in the present tense. Schrijver supposes that its athematic present was used clause-initially and the thematic conjugation was used when that was not the case.Vocabulary
The vast majority of reliably reconstructible lexical items in Proto-Celtic have good Indo-European etymologies, unlike what is found in, for example, the Greek language—at least 90% according to Matasovic. These include most of the items on the Swadesh list of basic vocabulary. But a few words that do not have Indo-European cognates, so may be borrowings from substrate or adstrate Pre-Indo-European languages, are also from basic vocabulary, including *bodyo- ‘yellow’, *kani "good," and *klukka "stone." It is notable that fully 32 items have been reconstructed for Proto-Celtic with the meaning "fight."Examples of morphology derivation from PIE
Two examples of verbs
| Pronoun | PIE | PC |
| 1st Sg. | *bʰéroh₂ | *berū |
| 2nd Sg. | *bʰéresi | *beresi |
| 3rd Sg. | *bʰéreti | *bereti |
| 1st Pl. | *bʰéromos | *beromosi |
| 2nd Pl. | *bʰérete | *beretesi |
| 3rd Pl. | *bʰéronti | *beronti |
| Pronoun | PIE | PC |
| 1st Sg. | *h₁ésmi | *esmi |
| 2nd Sg. | *h₁ési | *esi |
| 3rd Sg. | *h₁ésti | *esti |
| 1st Pl. | *h₁smós | *esmosi |
| 2nd Pl. | *h₁sté | *estes |
| 3rd Pl. | *h₁sénti | *senti |