Proto-Celtic is generally thought to have been spoken between 1300 and 800 BC, after which it began to split into different languages.
So, the main sources for reconstruction come from Insular Celtic languages with the oldest literature found in Old Irish[1] and Middle Welsh,[2] dating back to authors flourishing in the 6th century AD.
[3] The fact that it is possible to reconstruct a Proto-Celtic word for 'iron' (traditionally reconstructed as *īsarnom) has long been taken as an indication that the divergence into individual Celtic languages did not start until the Iron Age (8th century BC to 1st century BC); otherwise, descendant languages would have developed their own, unrelated words for their metal.
The following sound changes are shared with the Italic languages in particular, and are cited in support of the Italo-Celtic hypothesis.
[7] One change shows non-exact parallels in Italic: vocalization of syllabic resonants next to laryngeals depending on the environment.
Similar developments appear in Italic, but for the syllabic nasals *m̩, *n̩, the result is Proto-Italic *əm, *ən (> Latin em ~ im, en ~ in).
PIE *sp- became Old Irish s (f- when lenited, 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.
Thus, Gaulish petuar[ios], Welsh pedwar "four", but Old Irish cethair and Latin quattuor.
Insofar as this new /p/ 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.
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: 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 PC vowel system is highly comparable to that reconstructed for PIE by Antoine Meillet.
The number of cases is a subject of contention:[16] while Old Irish may have only five, the evidence from Continental Celtic is considered[by whom?]
These cases were nominative, vocative, accusative, dative, genitive, ablative, locative and instrumental.
E.g. *ɸlāmā 'hand' (feminine) (Old Irish lám; Welsh llaw, Cornish leuv, Old Breton lom) E.g. *sūlis 'sight, view, eye' (feminine) (Brittonic sulis ~ Old Irish súil) E.g. *mori 'body of water, sea' (neuter) (Gaulish Mori- ~ Old Irish muir ~ Welsh môr) E.g. *bitus 'world, existence' (masculine) (Gaulish Bitu- ~ Old Irish bith ~ Welsh byd ~ Breton bed) E.g. *beru "rotisserie spit" (neuter) Before the *-s of the nominative singular, a velar consonant was fricated to *-x : *rīg- "king" > *rīxs.
E.g. *abū "river" (feminine) E.g. *anman "name" (neuter) Generally,*s-stems contain an *-es-, which becomes *-os in the nominative singular: *teges- 'house' > *tegos.
[23] Consonant-stem adjectives also existed but were vanishingly rare, with only relics in Old Irish like té "hot" < *teɸents.
These endings are:[27]: 62–67 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.[30] Many suffixless preterite formations featured reduplication.
[31] Primary subjunctive formations in Proto-Celtic generally use the e-grade of the verb root, even if the present stem uses the zero-grade.
[33][19]: 140 The third-person imperative endings in Insular Celtic, Gaulish and Celtiberian have completely separate origins from each other.
[37] 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.