a high tone. (These include prepositions, clitic pronouns for subject and object, impersonal subject pronouns and focus markers.) There are therefore three possible "accentual patterns" in word roots. Phonetically there are three tones on long vowels: high, low and falling: On a long vowel or diphthong, a sequence of high-low is realised as a falling tone. On a long vowel or diphthong, a sequence of low-high is realised as high-high. (Occasionally, it is a rising tone.) This use of tone may be characterized as pitch accent. It is similar to that in Oromo. Stress is connected with tone. The high tone has strong stress; the falling tone has less stress and the low tone has no stress. When needed, the conventions for marking tone on written Somali are as follows: acute accent - high tone grave accent - low tone circumflex - falling tone Tones on long vowels are marked on the first vowel symbol. Phonotactics The syllable structure of Somali is (C)V(C). Root morphemes usually have a mono- or di-syllabic structure. Clusters of two consonants do not occur word-initially or word-finally, i.e., they only occur at syllable boundaries. The following consonants can be geminate: , , , , , , , and . The following cannot be geminate: , and the fricatives. Two vowels cannot occur together at syllable boundaries. Epenthetic consonants, e.g. and , are therefore inserted. Phonological processes Allophones The voiced stops (, , and ) are devoiced in word-initial and word-final position. Between two vowels they become fricatives. The voiceless stops and are realised as and in syllable-final position. is realised as in syllable-final position. Between vowels, is usually voiced to . All vowels are nasalised before or after a nasal consonant. Epenthesis When a vowel occurs in word-initial position, a glottal stop () is inserted before it. Sandhi Phonological changes occur at morpheme boundaries (sandhi) for specific grammatical morphemes. There may be assimilation or elision. One unusual change which can occur is to . Coalescence also occurs. This is a kind of external sandhi in which words join, undergoing phonological processes such as elision. In Somali it is sometimes obligatory and sometimes it is dependent on the speech style. Vowel harmony Roots have front-back vowel harmony. There is also a process of vowel harmony in strings longer than a word, known as "harmonic groups". Prosody Intonation (as opposed to tone, see above) does not carry