Onset Italian allows up to three consonants in syllable-initial position, though there are limitations: CC + any voiceless stop or . E.g. spavento ('fright') + any voiced stop, . E.g. srotolare ('unroll') , or any stop + . E.g. frana ('landslide') , or any stop except + . E.g. platano ('planetree') , or any stop or nasal + . E.g. fiume ('river'), vuole ('he/she wants'), siamo ('we are'), suono ('sound') In words of foreign (mostly Greek) origin which are only partially assimilated, other combinations such as (e.g. pneumatico), (e.g. mnemonico), (e.g. tmesi), and (e.g. pseudo-) occur. As an onset, the cluster + voiceless consonant is inherently unstable. Phonetically, word-internal s+C normally syllabifies as 'toad', (neighborhood of Rome). Phonetic syllabification of the cluster also occurs at word boundaries if a vowel precedes it without pause, e.g. 'the history', implying the same syllable break at the structural level, , thus always latent due to the extrasyllabic , but unrealized phonetically unless a vowel precedes. A competing analysis accepts that while the syllabification is accurate historically, modern retreat of i-prosthesis before word initial +C (e.g. erstwhile con isforzo 'with effort' has generally given way to con sforzo) suggests that the structure is now underdetermined, with occurrence of or variable "according to the context and the idiosyncratic behaviour of the speakers." CCC + voiceless stop or + . E.g. spregiare ('to despise') + voiced stop + . E.g. sbracciato ('with bare arms'), sdraiare ('to lay down'), sgravare ('to relieve') + + . E.g. sclerosi ('sclerosis') + + . E.g. sbloccato ('unblocked') or any stop + + . E.g. priego (antiquated form of prego 'I pray'), proprio ('(one's) own' / proper / properly), pruovo (antiquated form of provo 'I try') or any stop or nasal + + . E.g. quieto ('quiet'), continuiamo ('we continue') The last combination is however rare and one of the approximants is often vocalised, e.g. quieto , continuiamo Nucleus The nucleus is the only mandatory part of a syllable (for instance, a 'to, at' is a word) and must be a vowel or a diphthong. In a falling diphthong the most common second elements are or but other combinations such as idea , trae may also be interpreted as diphthongs. Combinations of with vowels are often labelled diphthongs, allowing for combinations of with falling diphthongs to be called triphthongs. One view holds that it is more accurate to label as consonants