Phonotactics (from Ancient Greek phōnḗ 'voice, sound' and taktikós 'having to do with arranging')[1] is a branch of phonology that deals with restrictions in a language on the permissible combinations of phonemes.
[3] The English syllable (and word) twelfths /twɛlfθs/ is divided into the onset /tw/, the nucleus /ɛ/ and the coda /lfθs/; thus, it can be described as CCVCCCC (C = consonant, V = vowel).
For instance, English allows at most three consonants in an onset, but among native words under standard accents (and excluding a few obscure loanwords such as sphragistics), phonemes in a three-consonantal onset are limited to the following scheme:[4] This constraint can be observed in the pronunciation of the word blue: originally, the vowel of blue was identical to the vowel of cue, approximately [iw].
The SSP expresses a very strong cross-linguistic tendency, however, it does not account for the patterns of all complex syllable margins, as there are both initial as well as final clusters violation the SSP, in two ways: the first occurs when two segments in a margin have the same sonority, which is known as a sonority plateau.
These margins are known as reversals and occur in some languages including English (steal [stiːɫ], bets /bɛts/) or French (dextre /dɛkstʁ/ but originally /dɛkstʁə/, strict /stʁikt/).