The purpose of this study is to clarify changes in ideas about bushido, especially focusing on the theories of the three historians Shigeno Yasutsugu, Matsumoto Aijū, and Naitō Chisō, which were formulated before the “bushido boom” of around 1905 and until the rise of modern bushido. In this paper, the theories of these three writers will be considered from two main perspectives: “the source of bushido” and “bushido’s ethics and morality”. On the “source of bushido”, Shigeno believed bushido to be something that existed from the beginning of the foundation of the country and saw its roots in the Mononobe and Ōtomo families that served the imperial household. Like Shigeno, Matsumoto thought the source of bushido was found in ancient times and the Yamato Court. In previous research, it was asserted that Shigeno was the first return to the source of bushido and emphasise the connection between it and the emperor. Nevertheless, such a view can also be seen in Matsumoto’s work from the previous year. Naito, who wrote his bushido theory two years earlier than Matsumoto, saw the source of bushido as emanating from the generals Nitta and Kusunoki, who protected the imperial household during the Nanboku-chō period. Before the works of Shigeno and Matsumoto, there was also a theory on the origins of bushido based on an historical view inherited from the early modern period, which can be seen in the position of the “Nanchō seitō-ron” (controversy surrounding the Northern and Southern Courts) of the Mitogaku school of Japanese historical and Shintō studies to which they belonged. As for “bushido’s ethics and morality”, the words “ethics” (rinri) and “morality” (dōtoku) were not used in Shigeno and Matsumoto’s theories of bushido. They were critical of the trend at the time to bring historical research and modern ethics and moral education closer together. Thus, their theories of bushido focused on piecing together historical evidence. Naitō, however, used the word “ethics” (rinri) in his discourse. The third decade of the Meiji Period was a time when Japanese literary history was becoming increasingly associated with ethics and moral education. The fact that Naitō was one of the key figures in this movement was thought to be the reason why he spoke of bushido as a source of ethics and morality. In addition, it could be said that such historical trends at that time may have influenced the ideological theory of bushido combined ethics and morality later purported by the scholar Inoue Tetsujirō during the “bushido boom”.