A possible feature of the difference between two accents of a language. Lexical incidence differences involve the occurrence of different phonemes in the same word in the two accents in question and do not necessarily have implications for the phonological systems of the two accents, nor for the phonetic realisation of the phonemes in question. An example of a lexical incidence difference between northern and southern accents of English involves words such as pass, laugh, bath. In many northern accents these contain the vowel phoneme /æ/, whereas in the south the vowel is usually /ɑː/. Both accents have both phonemes, /æ/ in gas, mass, for instance, and /ɑː/ in father.