脂真微文之分，雖經前人論定，但各家歸字，頗有不同，而又莫能究其原始。本文發現，除於個別古文字聲符之認定可以更定外，脂真微文之開合口結構性對立，實為四部分立根本所在。以脂真為微文之合口變音，則一切扞格渙然可解。文中一一論列，並附重訂四部諧聲表，以竟其說。

The contrasts of chi 脂 vs. wei 微 and chen 真 vs. wen 文 respectively in the Old Chinese riming categories have long been acknowledged, yet the boundaries between each pair still remain uncertain. This paper proposes that the crucial feature that characterizes the contrast is [±round], a structural feature that eventually caused the split of chi-chen 脂真 from wei-wen 微文. Arguments, as well as the recognition of the sound symbols of the riming categories involved, are presented.

上古韻部；脂微分部；真文分部；開合口；變音

Old Chinese riming categories; round; chi 脂 vs. wei 微; chen 真 vs. wen 文; split