Vowel breaking or diphthongization is a vowel shift in which a monophthong becomes a diphthong. Lengthening also occurs if the preceding vowel is a close diphthong or . The merged vowel was a diphthong, transcribed or . Verb stems may never end in a long vowel or a diphthong. In Urdu, hamza usually represents a diphthong between two vowels. In the case of a diphthong or a digraph, the second vowel takes the diacritics. Monophthongization or smoothing is a vowel shift in which a diphthong becomes a monophthong. Indonesian has four diphthong phonemes only in open syllables. V can be realized as a doubled vowel or a diphthong. Syllables ending in a diphthong and consonant are rare in Classical Latin. Additionally, the digraph "ie" generally represents the phoneme , which is not a diphthong. The diphthong is pronounced in some dialects. The diphthong "oo" is pronounced as . Some linguists use the terms "diphthong" and "triphthong" only in this phonemic sense. The development of the Standard German diphthong "ei" reflects this early adoption.