水戶學分期的問題，尤其是針對後期水戶學成立的相關討論，是歷來研究所關注的重要課題。意即自前期水戶學到後期水戶學於思想層面的「轉化」形成是起於何時？值得注意的是，這裡的「轉化」就思想史進程來看， 其論題主要放在藤田幽谷思想的衡定。要之，幽谷思想的形成脈絡，除紹述前期水戶學外，更是受到荻生徂徠影響，以此為切入點，或可究明內中的思想構造。本文主要通過藤田幽谷於青年時期撰成的〈正名論〉為分析文本， 藉以窺探他的思想特質，由此來探討他承繼自前期水戶學「尊王敬幕」，加以對徂徠古學的吸收，並在「大政委任論」的脈絡下，扣緊著「勢」的闡說來指認名分論的演繹與流變。

Issues regarding the division of Mitogaku 水戶學 into different periods, particularly those concerning the establishment of later Mitogaku 後期水戶學, have been noteworthy topics in relevant research. Namely, when did the “transformation” begin from early Mitogaku 前期水戶學 to later Mitogaku? In terms of trends in intellectual history, the topic of “transformation” has primar¬ily emphasized discussions on the thoughts of Fujita Yūkoku藤田幽谷 (1774- 1826). In short, considering the context for the formation of Yūkoku’s ideas, they were not only a continuation of early Mitogaku, but also influenced by Ogyū Sorai 荻生徂徠 (1666-1728), both of which can be used as the point of entry to clarify the structure of his understandings. This article aims at inves¬tigating the characteristics of Yūkoku’s thoughts through a textual analysis of “Seimeiron” 正名論 ( “On the rectification of names ” ), which was written in his youth, and thereby explores his adoption of the concept “Sonnō Keibaku”尊王敬幕(reverence for the Tennō and respect for the Tokugawa Shogunate) from early Mitogaku as well as his assimilation of Sorai’s Classic Studies 徂徠古學. Furthermore, through an explanation of “zei” 勢 (trend), this article identifies the inferences and changes of “meibunron” 名分論 (theories on demarcating a person’s status) within the context of “Taisei-ininron” 大政委任論.