the old acute also lengthened vowels). In the emerging modern Polish, however, the long vowels were shortened again but sometimes (depending on dialect) with a change in quality (the vowels tended to become higher). The latter changes came to be incorporated into the standard language only in the case of long o and the long nasal vowel. The vowel shift may thus be presented as follows: long oral > short oral (certain dialects: , ) long oral > short oral (certain dialects: , or ) long oral or > short oral or long oral > short oral (certain dialects: ), written ó long oral > short oral , written u long nasal > short nasal , written ą Note that the that was once a long is still distinguished in script as ó, except in some words which were later respelled, such as , , (instead of etymological , , ). In most circumstances, consonants were palatalized when followed by an original front vowel, including the soft yer (ь) that was often later lost. For example: *dьnь became dzień ('day'), while *dьnьmъ became dniem ('day' instr.). Nasal vowels *ę and *ǫ of late Proto-Slavic merged (*ę leaving a trace by palatalizing the preceding consonant) to become the medieval Polish vowel , written ø. Like other Polish vowels, it developed long and short variants. The short variant developed into present-day ę, while the long form became , written ą, as described above. Overall: Proto-Slavic *ę > ię when short, ią when long (where the i represents palatalization of the preceding consonant) Proto-Slavic *ǫ > ę when short, ą when long The historical shifts are the reason for the alternations o:ó and ę:ą commonly encountered in Polish morphology: *rogъ ('horn') became róg due to the loss of the following yer (originally pronounced with a long o, now with ), and the instrumental case of the same word went from *rogъmъ to rogiem (with no lengthening of the o). Similarly, *dǫbъ ('oak') became dąb (originally with the long form of the nasal vowel), and in the instrumental case, *dǫbъmъ the vowel remained short, causing the modern dębem. Dialectal variation Polish dialects differ particularly in their realization of nasal vowels, both in terms of whether and when they are decomposed to an oral vowel followed by a nasal consonant and in terms of the quality of the vowels used. Also, some dialects preserve nonstandard