Fujaku was an important Buddhist thinker in Japan in the eighteenth century. In this essay I will discuss Fujaku's response to the argument that the Mahayana was not preached by the Buddha, which was one of the greatest problems for early-modern arguments in defense of the Buddha Dharma, and show the meaning of early-modern Buddhist thought through his thinking. Fujaku's Mahayana thought was an applied practical theory based on the Kegon classification of the Buddhist teachings. The classification of the teachings for him was not a conceptual theory, but the path put into practice on his own, and the steps on which his soul was ascending through his many lives in the future. He changed the focus away from "Mahayana not preached by the Buddha" into "the teachings by Buddhas in other worlds" where he would be born next, by the way of living the classification of the teachings. Furthermore, early modern rationality, as represented in Japanese intellectual history by Tominaga Nakamoto, gave rise to the religiosity for Fujaku to live the classification of the Buddhist doctrines. The connection of these two figures in early modern times influenced the development of modern Buddhism, and provided the theoretical basis for modern Buddhists such as Murakami Senjo.