 The two characters formerly belonged to two different Old Chinese rime groups (脂 and 微 groups, respectively) and could not possibly have had the same pronunciation back then.A similar situation is responsible for the existence of variant forms of the preposition with the meaning 'in; to', 于 and 於 in the modern (traditional) orthography.In both cases described above, the variants were merged into a single simplified Chinese character, 饥 and 于, by the mainland (PRC) authorities.