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".