Phonotactics

Phonotactics (from Ancient Greek phōnḗ "voice, sound" and taktikós "having to do with arranging") 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 phonotactical constraints.

Phonotactic constraints are highly language specific. For example, in Japanese, consonant clusters like /st/ do not occur. Similarly, the sounds /kn/ and /ɡn/ are not permitted at the beginning of a word in Modern English but are in German and Dutch, and were permitted in Old and Middle English. In contrast, in some Slavic languages /l/ and /r/ are used as vowels.

Syllables have the following internal segmental structure:

Both onset and coda may be empty, forming a vowel-only syllable, or alternatively, the nucleus can be occupied by a syllabic consonant. Phonotactics is known to affect second language vocabulary acquisition.