This paper describes the microhistory of the change
→
(syllabic velar nasal becomes syllabic bilabial nasal) by focusing on the following aspects: first, the phonetic origin of , which is traced to labial assimilation of in particular phonetic environments; second, lexical diffusion and the role of variation between and in the propagation of the change; third, differential implementation of the change within the speech community, e.g. older speakers over age 49 have been bypassed by the change while young males in their teens and early 20's are the most advanced group of speakers in their use of ; fourth, the effect of the change on lexical items of the SC -class - 'five' is most affected by the change in terms of the number of speakers who use the -pronunciation and other items are found to be less affected; and fifth, the time when the change entered Cantonese, which appears to coincide with the period of World War II.