〈體性〉、〈定勢〉是劉勰風格論中的兩大範疇，然〈體性〉一文主要探析文體與作者才性，屬於風格形成的主觀因素；〈定勢〉所談則偏重文體與語勢，風於風格形成的客觀因素，兩皷雖同為風格論，討論的卻是主、客觀的不同。在此試圖藉由文本探求「勢」之意涵，以及「情」、「體」、「勢」三者之關係，並進一步推求劉勰創作〈定勢〉之目的與動機，以明〈定勢〉之作用與價值。

Ti-xing, Ding-shi are two ranges of Xie Liu’s thinking about writing style. Ti-xing investigates writing form and author’s temperament. It’s belong to the subjectivity cause of the forming style. Ding-shi investigates writing form and the trend of language. It’s belong to the objectivity cause of the forming style. The paper tries to investigates the meaning about trend and the relation between feeling, form and trend. It looks for the writing intention and reason.