addition to synalepha across word boundaries, sequences of vowels in hiatus become diphthongs in fast speech; when this happens, one vowel becomes non-syllabic (unless they are the same vowel, in which case they fuse together) as in ('poet') and ('teacher'). Similarly, the relatively rare diphthong may be reduced to in certain unstressed contexts, as in , . In the case of verbs like ('relieve'), diphthongs result from the suffixation of normal verbal morphology onto a stem-final (that is, would be || + ||). This contrasts with verbs like ('to extend') which, by their verbal morphology, seem to have stems ending in . Spanish also possesses triphthongs like and, in dialects that use a second person plural conjugation, , , and (e.g. , 'ox'; , 'you change'; , '(that) you may change'; and , 'you ascertain'). Non-syllabic and can be reduced to , , as in ('beatitude') and ('poetess'), respectively; similarly, non-syllabic can be completely elided, as in (e.g. 'right away'). The frequency (though not the presence) of this phenomenon differs amongst dialects, with a number having it occur rarely and others exhibiting it always. Prosody Spanish is usually considered a syllable-timed language. Even so, stressed syllables can be up to 50% longer in duration than non-stressed syllables. Although pitch, duration, and loudness contribute to the perception of stress, pitch is the most important in isolation. Primary stress occurs on the penultima (the next-to-last syllable) 80% of the time. The other 20% of the time, stress falls on the ultima and antepenultima (third-to-last syllable). Nonverbs are generally stressed on the penultimate syllable for vowel-final words and on the final syllable of consonant-final words. Exceptions are marked orthographically (see below), whereas regular words are underlyingly phonologically marked with a stress feature [+stress]. In addition to exceptions to these tendencies, particularly learned words from Greek and Latin that feature antepenultimate stress, there are numerous minimal pairs which contrast solely on stress such as sábana ('sheet') and sabana ('savannah'), as well as límite ('boundary'), limite ('[that] he/she limit') and limité ('I limited'). Lexical stress may be marked orthographically with an acute accent (ácido, distinción, etc.). This is done according to the mandatory stress rules of Spanish orthography, which are similar to the tendencies above (differing with words like distinción) and are defined so as to unequivocally indicate where the stress lies in a given written word. An acute accent may also be used to