phonotactics

Phonotactics (from Ancient Greek and ) is a branch of phonology that deals with restrictions in a language on the permissible combinations of phonemes. Phonotactics defines permissible syllable structure, consonant clusters and vowel sequences by means of phonotactic constraints.

Phonotactic constraints are highly language-specific. For example, in Japanese, consonant clusters like do not occur. Similarly, the clusters and are not permitted at the beginning of a word in Modern English but are permitted in German and were permitted in Old and Middle English. In contrast, in some Slavic languages and are used alongside vowels as syllable nuclei.