on). In the variety of Romance underlying Sardo and some other dialects of the islands, the ten vowels simply fell together pairwise: in no way are Latin e, ē, say, reflected differently. In Proto-Western-Romance, the ancestor of French, Iberian, Italian north of the Spezia-Rimini line, etc., however, things happened differently: Latin /a ā/ merged totally, as in Sardo, but the other vowels all behaved differently. Upon losing the feature of length, Latin /ī ū/ merged with nothing, but the short high vowels, front and back, merged with the long mid vowels: thus, Latin /i ē/ are uniformly reflected as PWRom. *ẹ (in the standard Romance notation), and /u ō/ become *ọ. PWRom. *ẹ is reflected in French (in open syllables) as /wa/ (spelled oi); voile "sail", foin "hay", doigt "finger", quoi "what", are from Latin vēlum, fēnum, digitus (via *dictu), quid, respectively. There is no way of telling in French which one of the two Latin vowels is the source of any given /wa/. Another example is provided by Japonic languages. Proto-Japanese had 8 vowels; it has been reduced to 5 in modern Japanese, but in Yaeyama, the vowel mergers progressed further, to 3 vowels. Split In a split (Hoenigswald's "secondary split"), a new contrast arises when allophones of a phoneme cease being in complementary distribution and are therefore necessarily independent structure points, i.e. contrastive. This mostly comes about because of some loss of distinctiveness in the environment of one or more allophones of a phoneme. A simple example is the rise of the contrast between nasal and oral vowels in French. A full account of this history is complicated by the subsequent changes in the phonetics of the nasal vowels, but the development can be compendiously illustrated via the present-day French phonemes /a/ and /ã/: Step 1: *a > *ã when a nasal immediately follows: *čantu "song" > (still phonemically ); Step 2: at some point in the history of French when speakers consistently stopped making an oral closure with the tongue, we had , that is (if not ) and finally, with the loss of the final stop, modern French chant "song", distinct from French chat "cat" solely by the contrast between the nasal and the oral articulation of the vowels, and thus with many other forms in which /a/ and contrast. Note 1: the nasalization of a vowel before a nasal is found very widely in the