Vowel whose quality does not change over the duration of the vowel is called a monophthong. Monophthongs are sometimes called "pure" or "stable" vowels. A vowel sound that glides from one quality to another is called a diphthong, and a vowel sound that glides successively through three qualities is a triphthong. All languages have monophthongs and many languages have diphthongs, but triphthongs or vowel sounds with even more target qualities are relatively rare cross-linguistically. English has all three types: the vowel sound in "hit" is a monophthong , the vowel sound in "boy" is in most dialects a diphthong , and
Triphthong realizations of are possible, and are regarded as "very strongly Cockney". Among these, the triphthongal realization of occurs most commonly. There is not a complete agreement about the distribution of these; according to , they "occur in sentence-final position", whereas according to , these are "most common in final position". Bernese German has the following triphthongs: Northern Bavarian has the following triphthongs: The Northern Bavarian triphthongs have evolved from combinations of former long vowels or diphthongs from the Middle High German (MHG) period and vocalized "r". Portuguese: Some Portuguese triphthongs appear in places where some speakers can break the first