To these must be further added some striking peculiarities in phonology.
(vi.) Assimilation of _p_ to a _q^u_ in a following syllable as in Lat. _quinque_ = Ir. _cóic_, compared with Sans. _pánca_, Gr. [Greek: pente], 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_, _quando_, _quinque_; Falisc. _cuando_) and Osco-Umbrian, better called Safine (Osc. _pod_, Umb. _panu_- [for *_pando_], Osc.-Umb. _pompe_-, "five," in Osc. _pumperias_ "nonae," Umb. _pumpedia_-, "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_.
From these primitive affinities we must clearly distinguish the numerous words taken into Latin from the Celts of north Italy within the historic period; for these see especially an interesting study by J. Zwicker, _De vocabulis et rebus Gallicis sive Transpadanis apud Vergilium_ (Leipzig dissertation, 1905).
6. _Greek and Italic._--We have seen above (§ 4, i., ii., iii.) certain broad characteristics which the Greek and the Italic groups of language have in common. The old question of the degree of their affinity may be briefly noticed. There are deep-seated differences in morphology, phonology and vocabulary between the two languages--such as (a) the loss of the forms of the ablative in Greek and of the middle voice in Latin; (b) the decay of the fricatives (_s_, _v_, _^i_) in Greek and the cavalier treatment of the aspirates in Latin; and (c) the almost total discrepancy of the vocabularies of law and religion in the two languages--which altogether forbid the assumption that the two groups can ever have been completely identical after their first dialectic separation from the parent language. On the other hand, in the first early periods of that dialectic development in the Indo-European family, the precursors of Greek and Italic cannot have been separated by any very wide boundary. To this primitive neighbourhood may be referred such peculiarities as (a) the genitive plural feminine ending in -_asom_ (Gr. [Greek: -aôn], later in various dialects [Greek: -eôn, -ôn, -an]; cf. Osc. _egmazum_ "rerum"; Lat. _mensarum_, with -_r_- from -_s_-), (b) the feminine gender of many nouns of the -_o_- declension, cf. Gr. [Greek: hê hodos], Lat. _haec fagus_; and some important and ancient syntactical features, especially in the uses of the cases (e.g. (c) the genitive of price) of the (d) infinitive and of the (e) participles passive (though in each case the forms differ widely in the two groups), and perhaps (f) of the dependent moods (though here again the forms have been vigorously reshaped in Italic). These syntactic parallels, which are hardly noticed by Kretschmer in his otherwise careful discussion (_Einleit._ p. 155 seq.), serve to confirm his general conclusion which has been here adopted; because syntactic peculiarities have a long life and may survive not merely complete revolutions in morphology, but even a complete change in the speaker's language, e.g. such Celticisms in Irish-English as "What are you after doing?" for "What have you done?" or in Welsh-English as "whatever" for "anyhow." A few isolated correspondences in vocabulary, as in _remus_ from *_ret-s-mo_-, with [Greek: eretmos] and in a few plant-names (e.g. [Greek: prason] and _porrum_), cannot disturb the general conclusion, though no doubt they have some historical significance, if it could be determined.