本文以兵家主張為中心，探討先秦至西漢「勢」概念的義涵發展。往前並追溯「勢」 的初義，以探究日後「勢」義涵之所以豐富的緣由；最後則試著從「相對關係」的角度，分 析「勢」的哲學義涵。 本文首先藉著文字學及上古音韻學，證明「勢」概念的晚出及其與「藝」字的密切關係。 並分析日後「勢」概念的諸種豐富義涵，皆由「藝」字初形「埶」及初義「種植」衍伸而來。 隨後則闡明：直至春秋時代為止，仍是「勢」概念的發軔期，文獻記載殊少，只有被稱 為春秋末期之作的《孫子兵法》才大量使用。而春秋時代之「勢」義涵，都絲毫未觸及法家 君臣上下的統治關係。 值得吾人注意的是，兵家系統的「勢」概念主要不是在強調地勢的險要，而是用之於戰 略及戰術思考上。因應戰場上各種瞬息萬變的情勢，善於通權達變製造有利於我方的態勢， 才是兵家「勢」概念的重點。 本文最後指出：「勢」概念隱涵著「相對關係」的思考。亦即，從「相對關係」的角度， 幾乎可以全盤解釋「勢」概念所涵的時間觀、空間觀。其中兵家的「勢」概念著眼於動態多 變的「敵我關係」，因而其時空觀具有較大的彈性。

　　　　　This article aims at an analysis of the development of the notion of shih in the military school of ancient China. The first section of this paper traces the etymological origins and the evolution of the notion of shih and indicates that this very notion was derived from "plow. " The second part of this paper is devoted to an analysis of the notion of shih in the military school since late Ch'un-ch'iu period. I argue that the notion of shih as conceived of by thinkers of the military school is centered upon the strategies and tactics in the battle fields. This paper reaches the conclusion that the notion of shih implies some ideas of relativity. In other words, the notions of time and space in concept of shih can best be analyzed in the context of relativity.