(iv.) _Accentuation._--One marked innovation common to the western groups as compared with what Greek and Sanskrit show to have been an earlier feature of the Indo-European parent speech was the development of a strong expiratory (sometimes called stress) accent upon the first syllable of all words. This appears early in the history of Italic, Celtic, Lettish (probably, and at a still later period) in Germanic, though at a period later than the beginning of the "sound-shifting." This extinguished the complex system of Indo-European accentuation, which is directly reflected in Sanskrit, and was itself replaced in Latin and Oscan by another system already mentioned, but not in Latin till it had produced marked effects upon the language (e.g. the degradation of the vowels in compounds as in _conficio_ from _cón-facio_, _includo_ from _ín-claudo_). This curious wave of accentual change (first pointed out by Dieterich, _Kuhn's Zeitschrift_, i., and later by Thurneysen, _Revue celtique_, vi. 312, _Rheinisches Museum_, xliii. 349) needs and deserves to be more closely investigated from a chronological standpoint. At present it is not clear how far it was a really connected process in all the languages. (See further Kretschmer, _op. cit._ p. 115, K. Brugmann, _Kurze vergleichende Grammatik_ (1902-1904), p. 57, and their citations, especially Meyer-Lübke, _Die Betonung im Gallischen_ (1901).)
To these larger affinities may be added some important points in which the Italic group shows marked resemblances to other groups.
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 [Greek: phatis] with Attic [Greek: basis], &c.) by an -_n_- suffix, as in Lat. _mentio_ (stem _mention_-) = Ir. (_er_-)_mitiu_ (stem _miti-n_-), contrasted with the same word without the _n_-suffix in Sans. _mati_-, Lat. _mens_, Ind.-Eur. *_mn-ti_-. A similar extension (shared also by Gothic) appears in Lat. _iuventu-t_-, O. Ir. _óitiu_ (stem _oiliut_-) beside the simple -_tu_- in nouns like _senatus_.