This paper aims to examine the origin and development of substance (substantia) and essence (essentia) theories in Civil Law, in its three main areas, i.e. those related to thing (res) (specificatio; ususfrutus; classifications of thing), to fact (factum) (error in substantia; essentialia, naturalia and accidentialia negotii; form ad substantiam) and to person (persona) (holder or carrier of rights and obligations), in chronological sequence from Roman Law, Medieval Law, Early Modern Law to Late Modern Law, and to track down how they are formed under the strong influence of Philosophy especially of Aristotelian Substantialism, from the era of the medieval Glossators, and therefore have two big shortcomings: first, there is no substance or essence in absolutely objective sense, and because of this a subjective turn to the parties’s cognition happened; second, the definition method only using sufficient and necessary condition is defective and can be supplemented with Typenlehre (type theory), Wittgenstein’s ‘family resemblances’ theory and ‘prototype’ theory in Cognitive Linguistics. Keywords essence, specification, error in substantia, essentialia negotii, form

本文旨在按歷史時序檢視民法上關於「實質」（substantia；substance）與「本質」（essentia；essence）的各個理論，亦即物（加工；用益權；物的分類）、事（實質錯誤；法律行為要素、常素、偶素；實質性形式）、人（權利義務載體）這民法學三大領域的「實質」與「本質」理論，在羅馬法、中世紀法、近代法與現代法上的起源與發展，並考證它們如何從中世紀注釋法學派開始，便一直在古典哲學尤其是亞里士多德實體（本體、存有、存在、所是、實質）哲學的強烈影響下演變而成，因而遺傳了哲學上「實質主義」與「本質主義」的兩大缺陷：其一，絕對客觀的「實質」或「本質」並不存在；這促成了關注點向當事人主觀認知的轉向。其二，充分必要條件式的定義方法有其不足；它可由「類型」式思維、維特根斯坦的「家族相似」思維與認知語言學的「原型（元型）」思維予以彌補。 關鍵詞 本質 加工 實質錯誤 法律行為要素 形式