Sonority Sequencing Principle

The Sonority Sequencing Principle (SSP) is a phonotactic principle that aims to outline the structure of a syllable in terms of sonority.

In any syllable, the center of the syllable, namely the syllable nucleus, or the vowel, constitutes a sonority peak that is preceded and/or followed by a sequence of segments--consonants--with progressively decreasing sonority values (i.e., the sonority has to fall toward both edges of the syllable). The sonority values of segments are determined by a sonority hierarchy.

A good example for the SSP in English is the one-syllable word "trust": The first consonant in the syllable onset is "t", which is a stop, the lowest on the sonority scale; next is "r", a liquid which is more sonorous, then we have the vowel "u" (IPA: ʌ) - the sonority peak; next, in the syllable coda, is "s", a fricative, and last is another stop, "t".

Some languages possess syllables that violate the SSP (Russian and English, for example) while other languages strictly adhere to it, even requiring larger intervals on the sonority scale: In Italian for example, a syllable-initial stop must be followed by either a liquid, a glide or a vowel, but not by a fricative. Some languages allow a sonority "plateau"; that is, two adjacent tautosyllabic consonants with the same sonority level. Modern Hebrew is an example of such language.