As a phonological unit the syllable performs several functions, that may be combined into the main three: constitutive, distinctive and identificatory.
The constitutive function of the syllable manifests itself in the fact that the syllable forms higher-level units - words, accentual or rhythmic groups, utterances. Two aspects of this function can be emphasized. On the one hand, the syllable is a unit in which segmental phonemes are realized. L. Bondarko has proved experimentally that the relations between the distinctive features of the phonemes and their acoustic correlates can be revealed only within the syllable. On the other hand, within a syllable or a sequence of syllables prosodic (or suprasegmental) features of speech are also realized. These are distinctive variations in loudness (stress) in pitch (tone), and in duration (tempo, length). Thus syllables may be stressed and unstressed, high, mid or low, rising or falling, long or short. All these prosodic features are significant for constituting the stress—pattern of a word and the tonal and rhythmic structures of an utterance.
In forming words and utterances the syllable performs the delimitative function which is inseparable from the constitutive function. Some syllables can occur only word-initially (/ɡr/, /str/) and others only word-finally; /tn/, /dn/, /stl/ thus making the boundaries between words.
The distinctive function of the syllable is to differentiate words and word combinations. It has been mentioned that phonemes exist and function within the syllable. Therefore words are actually differentiated by the syllable as one articulatory and perceptible unit. For instance, the monosyllabic words /bi :t/ "beat" and /b i :d/ "bead" differ not only in their consonant phonemes/t/and /d/, but also in the length of/h/, which is conditioned by the neighbouring fort is and lenis consonants- Such words as /ɡɑ:dn/ "garden" - /ɡɑ:dz/ "guards", /bi:tn/ "beaten" - /bi:ts/ "beats" are distinguished not only by the phonemes /n/ versus /z/ and /n/ versus /s/ but also by their syllables as bisyllabic and monosyllabic words.
V. Vassilyev notes that the existence of such pairs of words makes it possible to consider syllabicity the only distinctive feature of the words and, on this account he distinguishes a separate phonological unit - the syllabeme.
Syllable division (syllabification) is very important too in distinguishing words and utterances.
The distinctive role of syllabification is illustrated by examples like
/naɪˈtreit/ "nitrate" - /ˈnaɪt ˈreɪt/ night-rate,
/ǝ ˈneɪm/ "a name" — /ǝn ˈeɪm/ "an aim",
/wil ˈəʊn/ "we'll own" — /wi ˈləʊn/ "we loan",
/aɪ ˈskri:m/ "I scream" - /aɪs ˈkri:m/ "ice cream",
Due to the distinctive importance of syllable division, the syllabic boundary is often regarded by the American descriptivists as a separate phonological unit — the juncture phoneme.
There are two types of juncture: open and close. Open juncture (or open transition) occurs between syllables, i.e. between two articulatory units. It may also be called intersyllabic juncture. Thus, in "we'll own" /wil ˈəʊn/ the open juncture is between /I/ and /əʊ/, and in "we loan" /wi ˈləʊn/ it is between /i/ and /I/;
Close juncture (or close transition) occurs between sounds within one syllable, i.e. within one articulatory unit. Therefore, the transitions from one sound to another are closer within a syllable than between syllables. Thus in "we loan" /wi ˈləʊn/ the close juncture is between /I/ and ləʊ/, /əʊ/ and /n/. This juncture may also be called intrasyllabic juncture.
The latest acoustic investigations of juncture show that the factors determining an open or a close juncture are the duration of the sounds, their intensity and formant transitions. Thus, according to the data obtained by I. Lehiste, the initial /n/ in "a nice man" is longer than the final /n/ in "an iceman". The pre-junctural /n/ has falling intensity, while the post-junctural /n/ has rising intensity. Formant transitions of /n/ and /aɪ/ are different in the contrasted pairs.
While the phonetic realization of open juncture is described by different phoneticians in approximately the same terms, there is less uniformity in their phonological interpretation of the phenomena. Some phoneticians consider the open juncture to be a segmental phoneme, others consider it a suprasegmental phoneme or a phoneme in its own right.