In the study of sound change and variation, merger of two phonetic categories is widely-observed
and well documented; on the contrary, the reversal of a merger, i.e. two merged categories
becoming distinct again, is much less studied and often considered to be impossible. In this talk, I
will go through (1) a recent study on a vowel merger reversal in Shanghainese (Wu, Sinitic) that is
attributed to language contact with Mandarin Chinese, and (2) some work-in-progress on merger
reversal in spontaneous phonetic imitation in Hong Kong Cantonese.