of any pharyngealization or velarization, . (The classical pronunciation of pharyngealization still occurs in the Mehri language, and the similar sound without velarization, , exists in other Modern South Arabian languages.) Other changes may also have happened. Classical Arabic pronunciation is not thoroughly recorded and different reconstructions of the sound system of Proto-Semitic propose different phonetic values. One example is the emphatic consonants, which are pharyngealized in modern pronunciations but may have been velarized in the eighth century and glottalized in Proto-Semitic. Literary Arabic Vowels Consonants The phoneme is represented by the Arabic letter () and has many standard pronunciations. is characteristic of north Algeria, Iraq, and most of the Arabian peninsula but with an allophonic in some positions; occurs in most of the Levant and most of North Africa; and is standard in Egypt, coastal Yemen, and western Oman. Generally this corresponds with the pronunciation in the colloquial dialects. In Sudan and Yemen, as well as in some Sudanese and Yemeni varieties, it may be either or , representing the original pronunciation of Classical Arabic. and () are velar, post-velar, or uvular. is pronounced as velarized in الله , the name of God, q.e. Allah, when the word follows a, ā, u or ū (after i or ī it is unvelarized: bismi l–lāh ). The emphatic consonant was actually pronounced , or possibly —either way, a highly unusual sound. The medieval Arabs actually termed their language 'the language of the Ḍād' (the name of the letter used for this sound), since they thought the sound was unique to their language. (In fact, it also exists in a few other minority Semitic languages, e.g., Mehri.) Arabic has consonants traditionally termed "emphatic" (), which exhibit simultaneous pharyngealization as well as varying degrees of velarization (depending on the region), so they may be written with the "Velarized or pharyngealized" diacritic () as: . This simultaneous articulation is described as "Retracted Tongue Root" by phonologists. In some transcription systems, emphasis is shown by capitalizing the letter, for example, is written ; in others the letter is underlined or has a dot below it, for example, . Syllable structure In surface pronunciation, every vowel must be preceded by a consonant (which may include the glottal stop ). There are no cases of hiatus within a word (where two vowels occur next to each other, without an intervening consonant). Some words do have an underlying