A "Great Shift" of these occurred in English during the middle ages, when several of them became diphthongs.
One form of this concept is "r-colored" when the nucleus of a syllable is a rhotic segment, and this concept is often classified by its backness and height, which are determined by the position of the tongue. Harmony of them occurs in many Altaic languages, where those near the beginning of a word affect later ones, and some of them are not usually written in many Semitic languages. A "Great Shift" of these occurred in English during the middle ages, when several of them became diphthongs. FTP, name this linguistic concept, English examples of which include a and o.
One form of this concept is "r-colored" when the nucleus of a syllable is a rhotic segment, and this concept is often classified by its backness and height, which are determined by the position of the tongue.
{Vowel}s