The relative sonority theory, or the prominence theory, created by the Danish phonetician O. Jespersen, considers that sounds tend to group themselves according to their sonority.
Pronounced with uniform force, length and pitch, speech sounds differ in sonority (prominence, audibility or carrying power). The most sonorous sounds are vowels, less sonorous are sonorants /w, j, r, m, n, ŋ / and the least sonorous are noise consonants. O. Jespersen classifies sounds according to the degree of sonority in the following way (beginning with the most sonorous):
Sounds are grouped around the most sonorous ones, i.e. vowels (and sometimes sonants) which form the peak of sonority in a syllable. One peak of sonority is separated from another peak by sounds of lower sonority, i.e. consonants. The distance between the two points of lower sonority is a syllable , e.g. "October". The number of syllables is determined by the number of peaks of prominence. Thus in the word /melt/ "melt" there is one peak of sonority /e/ and the word is monosyllabic. In the word /metl/ "metal" there are two peaks of sonority - /e/ and /I/, separated by the least sonorous /t/, and consequently, there are two syllables.
Here are some more examples to illustrate the sonority theory: /wu:dn/ "wooden" /fild/ "filled", /fidll/"fiddle". In Czeck words like /krk/ ďkrk" and in English "pst" the sounds /I, r, s/ are sonorous peaks.
But there are cases that contradict Jespersen's theory.
e.g. /sta:/ "star", /skeɪt/ "skate", /nekst/ "next".
In these words the sound /s/ is more sonorous than /t/ and /k/ and forms the second peak of sonority. Yet, the words are monosyllabic.
It is evident that the relative sonority theory does not explain the mechanism of syllable formation. It only makes an attempt at explaining our perception of a syllable. Neither does it explain syllable division, as it does not say to which syllable the less sonorous sounds belong, e.g. /ǝn'aɪsmæn/ "an iceman" and /ǝ'naɪs'mæn/ "a nice man", /ǝn'eɪm/ "an aim" and /ə'neɪm/ "a name", "some addresses" and "summer dresses"
Nevertheless, the relative sonority. theory has been accepted by D. Jones and some other phoneticians.
The most widespread among Soviet linguists is the muscular tensiÓn (or the articulatory effort) theory which is known as Shcherba's theory.
According to this theory a syllable is characterized by variations in muscular tension. The energy of articulation increases at the beginning of a syllable, reaches its maximum with the vowel (or the sonant) and decreases towards the end of the syllable. So, a syllable is an arc of muscular tension. The boundaries between syllables are determined by the occurrence of the lowest articulatory energy.
There are as many syllables in a word as there are maxima of muscular tension in it, Cf. /tɑ:/ "tar" and /tɑ:/ "tower" (a reduced variant of /taʊǝ/). The sound /ɑ:/ jn the second example is pronounced with two articulatory efforts, so there are two arcs of muscular tension and, therefore, two syllables.
Consonants within a syllable are characterized by different distribution of muscular tension. In accordance with this, L. Schherba distinguished the following three types of consonants.