5. Italic and Celtic.—It is now universally admitted that the Celtic languages stand in a much closer relation than any other group to the Italic. It may even be doubted whether there was any real frontier-line at all between the two groups before the Etruscan invasion of Italy (see [Etruria]: Language; [Liguria]). The number of morphological innovations on the Indo-European system which the two groups share, and which are almost if not wholly peculiar to them, is particularly striking. Of these the chief are the following.
(i.) Extension of the abstract-noun stems in -ti- (like Greek φάτις with Attic βάσις, &c.) by an -n- suffix, as in Lat. mentio (stem mentiōn-) = Ir. (er-)mitiu (stem miti-n-), contrasted with the same word without the n-suffix in Sans. mati-, Lat. mens, Ind.-Eur. *mṇ-ti-. A similar extension (shared also by Gothic) appears in Lat. iuventū-t-, O. Ir. óitiu (stem oiliūt-) beside the simple -tu- in nouns like senātus.
(ii.) Superlative formation in -is-ṃmo- as in Lat. aegerrimus for *aegr-isṃmos, Gallic Οὐξισάμη the name of a town meaning “the highest.”
(iii.) Genitive singular of the o-stems (second declension) in -ī Lat. agri, O. Ir. (Ogam inscriptions) magi, “of a son.”
(iv.) Passive and deponent formation in -r, Lat. sequitur = Ir. sechedar, “he follows.” The originally active meaning of this curious -r suffix was first pointed out by Zimmer (Kuhn’s Zeitschrift, 1888, xxx. 224), who thus explained the use of the accusative pronouns with these “passive” forms in Celtic; Ir. -m-berar, “I am carried,” literally “folk carry me”; Umb. pir ferar, literally ignem feratur, though as pir is a neuter word (= Gr. πῦρ) this example was not so convincing. But within a twelvemonth of the appearance of Zimmer’s article, an Oscan inscription (Conway, Camb. Philol. Society’s Proceedings, 1890, p. 16, and Italic Dialects, p. 113) was discovered containing the phrase ůltiumam (iůvilam) sakrafỉr, “ultimam (imaginem) consecraverint” (or “ultima consecretur”) which demonstrated the nature of the suffix in Italic also. This originally active meaning of the -r form (in the third person singular passive) is the cause of the remarkable fondness for the “impersonal” use of the passive in Latin (e.g., itur in antiquam silvam, instead of eunt), which was naturally extended to all tenses of the passive (ventum est, &c.), so soon as its origin was forgotten. Fuller details of the development will be found in Conway, op. cit. p. 561, and the authorities there cited (very little is added by K. Brugmann, Kurze vergl. Gramm. 1904, p. 596).
(v.) Formation of the perfect passive from the -to- past participle, Lat. monitus (est), &c., Ir. léic-the, “he was left,” ro-léiced, “he has been left.” In Latin the participle maintains its distinct adjectival character; in Irish (J. Strachan, Old Irish Paradigms, 1905, p. 50) it has sunk into a purely verbal form, just as the perfect participles in -us in Umbrian have been absorbed into the future perfect in -ust (entelust, “intenderit”; benust, “venerit”) with its impersonal passive or third plural active -us(s)so (probably standing for -ussor) as in benuso, “ventum erit” (or “venerint”).
To these must be further added some striking peculiarities in phonology.
(vi.) Assimilation of p to a qṷ in a following syllable as in Lat. quinque = Ir. cóic, compared with Sans. pánca, Gr. πέντε, Eng. five, Ind.-Eur. *penqe.
(vii.) Finally—and perhaps this parallelism is the most important of all from the historical standpoint—both Italic and Celtic are divided into two sub-families which differ, and differ in the same way, in their treatment of the Ind.-Eur. velar tenuis q. In both halves of each group it was labialized to some extent; in one half of each group it was labialized so far as to become p. This is the great line of cleavage (i.) between Latinian (Lat. quod, quandō, quinque; Falisc. cuando) and Osco-Umbrian, better called Safine (Osc. pod, Umb. panū- [for *pandō], Osc.-Umb. pompe-, “five,” in Osc. půmperias “nonae,” Umb. pumpeḓia-, “fifth day of the month”); and (ii.) between Goidelic (Gaelic) (O. Ir. cóic, “five,” maq, “son”; modern Irish and Scotch Mac as in MacPherson) and Brythonic (Britannic) (Welsh pump, “five,” Ap for map, as in Powel for Ap Howel).
The same distinction appears elsewhere; Germanic belongs, broadly described, to the q-group, and Greek, broadly described, to the p-group. The ethnological bearing of the distinction within Italy is considered in the articles [Sabini] and [Volsci]; but the wider questions which the facts suggest have as yet been only scantily discussed; see the references for the “Sequanian” dialect of Gallic (in the inscription of Coligny, whose language preserves q) in the article [Celts]: Language.