Proto-Celtic language

These changes were 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 (R̥HR > RaHR)
• Laryngeals are lost:
  • before a following vowel (HV > V)
  • following a vowel in syllables before the accent (VHC´ > VC´)
  • following a vowel, resulting in compensatory lengthening, thus (VH > V̄)
  • between plosives in non-initial syllables (CHC > CC)
• Two adjacent dentals become two adjacent sibilants (TT > ss)

The following sound changes are shared with the Italic languages in particular, and are cited in support of the Italo-Celtic hypothesis.[8]

• Dybo's rule: long close vowels are shortened (or a laryngeal is lost) before resonant + stressed vowel.
  • 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.
• Possibly, vocalization of laryngeals to *ī between a *CR cluster and consonantal *j (CRHjV > CRījV)
• Syllabic laryngeals become *a (CHC > CaC)
• Syllabic resonants before a voiced unaspirated stop become *Ra (R̥D > RaD)
• *m is assimilated or lost before a glide:
  • mj > nj
  • mw > w
• *p assimilates to *kʷ when another *kʷ follows later in the word (p…kʷ > kʷ…kʷ)
• sVs > ss, sTVs > Ts

One change shows non-exact parallels in Italic: the vocalization of syllabic resonants next to laryngeals depending on the environment. Similar developments appear in Italic, but for the syllabic nasals *m̥, *n̥, the result is Proto-Italic *əm, *ən (> Latin em ~ im, en ~ in).

• Word-initially, HR̥C > aRC
• Before voiceless stops, CR̥HT > CRaT
• CR̥HV > CaRHV
• CR̥HC > CRāC

• Sequences of velar and *w merge into the labiovelars (it is uncertain if this preceded or followed the next change; that is, whether gw > b or gw > gʷ, but Schumacher 2004 argues on p. 372 that this change came first; moreover, it is also found in Proto-Italic, and thus arguably belongs to the previous section):
  • kw > kʷ
  • gw > gʷ
  • gʰw > gʷʰ
• gʷ > b
• Aspirated stops lose their aspiration and merge with the voiced stops (except that this counterfeeds the previous change, so *gʷʰ > *gʷ doesn't result in a merger):
  • bʰ > b
  • dʰ > d
  • gʰ > g
  • gʷʰ > gʷ
• *e before a resonant and *a (but not *ā) becomes *a as well (eRa > aRa): *ǵʰelH-ro > *gelaro > *galaro / *gérH-no > *gerano > *garano (Joseph's rule).
• Epenthetic *i is inserted after syllabic liquids when followed by a plosive:
  • l̥T > liT
  • r̥T > riT
• Epenthetic *a is inserted before the remaining syllabic resonants:
  • m̥ > am
  • n̥ > an
  • l̥ > al
  • r̥ > ar
• All remaining nonsyllabic laryngeals are lost.
• ē > ī
• ō > ū in final syllables
• Long vowels are shortened before a syllable-final resonant (V:RC > VRC); this also shortens long diphthongs. (Osthoff's law)

• Plosives become *x before a different plosive or *s (C₁C₂ > xC₂, Cs > xs)
• p > b before liquids (pL > bL)
• p > w before nasals (pN > wN)
• p > ɸ (except possibly after *s)
• ō > ā
• ew > ow
• uwa > owa

The following consonants have been reconstructed for Proto-Celtic:

In contrast to the parent language, Proto-Celtic does not use aspiration as a feature for distinguishing phonemes. So the Proto-Indo-European voiced aspirated stops *bʰ, *dʰ, *gʰ/ǵʰ merged with *b, *d, *g/ǵ. The voiced aspirate labiovelar *gʷʰ did not merge with *gʷ, though: plain *gʷ became *b in Proto-Celtic, while aspirated *gʷʰ became *gʷ. Thus, PIE *gʷen- 'woman' became Old Irish ben and Old Welsh ben, but PIE *gʷʰn̥- 'to kill, to wound' became Old Irish gonaid and Welsh gwanu.

Proto-Indo-European *p was lost in Proto-Celtic, apparently going through the stages *ɸ (as in the table above) and *h (perhaps attested by the toponym Hercynia if this is of Celtic origin) before being lost completely word-initially and between vowels. Adjacent to consonants, Proto-Celtic *ɸ underwent different changes: the clusters *ɸs and *ɸt became *xs and *xt respectively already in Proto-Celtic. PIE *sp- became Old Irish s (lenited f-, exactly as for PIE *sw-) and Brythonic f; while Schrijver 1995, p. 348 argues there was an intermediate stage *sɸ- (in which *ɸ remained an independent phoneme until after Proto-Insular Celtic had diverged into Goidelic and Brythonic), McCone 1996, pp. 44–45 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. (Similarly, Grimm's law did not apply to *p, t, k after *s in Germanic, and later the same exception occurred again in the High German consonant shift.)

In Gaulish and the Brittonic languages, a new *p sound has arisen as a reflex of the Proto-Indo-European *kʷ phoneme. Consequently, one finds Gaulish petuar[ios], Welsh pedwar "four", compared to Old Irish cethair and Latin quattuor. Insofar as this new /p/ fills the space in the phoneme inventory which was lost 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 when we wish to group the Celtic languages according to the way they handle this one phoneme. However a simple division into P- and Q-Celtic may be untenable, as it does not do justice to the evidence of the ancient Continental Celtic languages. The large number of unusual shared innovations among the Insular Celtic languages are often also presented as evidence against a P-Celtic 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 Celtic language classification in the genetic sense.

Q-Celtic languages may also have /p/ in loan words, though in early borrowings from Welsh into Primitive Irish /kʷ/ was used by sound substitution due to a lack of a /p/ phoneme at the time:

• Latin Patricius "Saint Patrick"' > Welsh > Primitive Irish Qatrikias > Old Irish Cothrige, later Pádraig;
• Latin presbyter "priest" > early form of word seen in Old Welsh premter primter > Primitive Irish qrimitir > Old Irish cruimther.

Gaelic póg "kiss" was a later borrowing (from the second word of the Latin phrase osculum pacis "kiss of peace") at a stage where p was borrowed directly as p, without substituting c.

The Proto-Celtic vowel system is highly comparable to that reconstructed for Proto-Indo-European by Antoine Meillet. The following monophthongs have been reconstructed:

Type	Front		Central		Back
	long	short	long	short	long	short
Close	iː	i			uː	u
Mid		e				o
Open			aː	a

The following diphthongs have also been reconstructed:

The morphology (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 the normal masculine, feminine and neuter, the three numbers were singular, plural and dual. The number of cases is a subject of contention:[11] 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 the stem. There are *o-stems, *ā-stems, *i-stems, *u-stems, dental stems, velar stems, nasal stems, *r-stems and *s-stems.

• makkʷos 'son' (masculine) (Old Irish mac ~ Welsh, Cornish and Breton mab)

• dūnom 'stronghold' (neuter)

E.g. *ɸlāmā 'hand' (feminine) (Old Irish lám; Welsh llaw, Cornish leuv, Old Breton lom)

E.g. *wolkās 'hawker' (masculine) (Gallic Latinised Volcae)

E.g. *sūlis 'sight, view, eye' (feminine) (Brittonic sulis ~ Old Irish súil)

E.g. *mori 'body of water, sea' (neuter) (Gallic Mori- ~ Old Irish muir ~ Welsh môr)

E.g. *bitus 'world, existence' (masculine) (Gallic Bitu- ~ Old Irish bith ~ Welsh byd ~ Breton bed)

E.g. *dānu 'valley river' (neuter?)

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.[12]

E.g. *rīxs 'king' (masculine) (Gallic -rix; Old Irish rí; Middle Welsh rhi, Old Breton ri, [13]Germanic *-riks, as seen in Haimariks, ancestor of the name "Henry" and related forms)

E.g. *druwits 'druid' (masculine) (Gallic druis; Old Irish druí; Middle Welsh dryw "druid; wren", Old Cornish druw)

E.g. *karnuxs 'carnyx' (masculine?)

E.g. *karants 'friend' (masculine) (Gallic carant-; Old Irish cara; Welsh câr "kinsman; friend", pl. ceraint, Breton kar "relative", pl. kerent)

Generally, nasal stems end in *-on-; this becomes *-ū in the nominative singular: *abon- "river" > *abū.

E.g. *abū 'river' (feminine) (Welsh afon, Breton (obs.) aven, Scottish Gaelic abhainn)

E.g. *anman 'name' (neuter) (Gaulish anuan-; Old Irish ainm; Breton anv; Welsh enw)

Generally, *s-stems end in *-es-, which becomes *-os in the nominative singular: *teges- 'house' > *tegos.

E.g. *tegos 'house' (masculine), Old Irish teg, tech, dative tigh; Welsh tŷ, Breton ti.

• 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.

E.g. *ɸatīr 'father' (masculine)

E.g. *mātīr 'mother' (feminine)

From comparison between early Old Irish and Gaulish forms it seems that Continental and Insular Celtic verbs were to develop differently and so the study of Irish and Welsh may have unduly weighted past opinion of proto-Celtic verbal 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 sg. Gaulish delgu "I hold", Old Irish tongu "I swear"
• imperative — seen in e.g. 3rd sg. Celtiberian usabituz, Gaulish appisetu
• subjunctive — seen in e.g. 3rd sg. Gaulish buetid "may he be", Celtiberian asekati

and four tenses:

• present — seen in e.g. Gaulish uediíu-mi "I pray", Celtiberian zizonti "they sow"
• preterite — seen in e.g. 3rd sg. Gaulish sioxti, Lepontic KariTe
• imperfect — perhaps in Celtiberian kombalkez, atibion
• future — seen in e.g. 3rd sg. Gaulish bissiet, Old Irish bieid "he shall be"

A probable optative mood also features in Gaulish (tixsintor) and an infinitive (with a characteristic ending -unei) in Celtiberian.[14][15]

Verbs were formed by adding suffixes to a verbal stem. The stem might be thematic or athematic, an open or a closed syllable.

Example conjugations

Scholarly reconstructions [7][16][17][18] may be summarised in tabular format.

Conjugation like *bere/o- 'bear, carry, flow'

Conjugation like *mārā- 'greaten, magnify, enlarge'