He was born the second son of Satō Nobuyoshi, chief retainer of the Iwamura domain in Mino, at the domain's residence in Hama-chō, Edo. The Satō family had served for generations as the domain's chief retainers. His given name was Taira, his common name Sutezō, and Issai was his pen name. Though raised in a samurai house, he was drawn to learning from early on.
He entered the service of the Iwamura domain as an attendant to Norihira, third son of lord Matsudaira Norimori. Norihira was a young man close in age who loved learning, and the two are said to have discussed scholarship as friends. This Norihira was the man who later inherited the Hayashi house, which oversaw the shogunate's learning, and took the name Hayashi Jussai.
After only about a year he was relieved of his post, and he then went to the Kamigata region to deepen his studies. He learned from renowned scholars such as Minagawa Kien of Kyoto and Nakai Chikuzan of Osaka, gaining broad knowledge centered on Neo-Confucianism. Through Nakai Chikuzan's teaching, he is said to have later grown drawn to Yōmeigaku as well.
Returning to Edo, he became a student of Hayashi Kanjun of the Hayashi house, which oversaw the shogunate's learning. Kanjun soon died, and when Norihira, whom Issai had once served, was adopted into the Hayashi house as Hayashi Jussai, Issai stayed on as Jussai's student. It was an unusual relationship in which a friend from youth became one's teacher.
Highly valued by Jussai for his scholarship, he became head of the Hayashi school and taught many students with Jussai. His pupils are said to have numbered three thousand, and many who would be active from the late Edo period into Meiji grew up under him, such as Yamada Hōkoku, Sakuma Shōzan, Watanabe Kazan, Yokoi Shōnan and Nakamura Masanao.
He is said to have begun writing the Genshi-roku, short passages recording his thoughts and teachings. He continued writing for more than forty years into old age, and together with three sequels the work is called the Genshi Shiroku. It contains many sayings on how to live and how to learn.
The Genshi-roku was published and came to be widely read. Saigō Takamori later made the Genshi Shiroku his lifelong favorite book and famously copied out 101 passages from it by hand. Issai's words supported the hearts of the activists of the late Edo period and are still read today.
In the Bansha no goku, in which students of Western learning were punished, his pupil Watanabe Kazan was accused. Because Issai did not act firmly to defend Kazan, he was later criticized for his words not matching his deeds. He is said to have been a strict man who always carried a watch and kept time rigorously.
When Jussai died, he was appointed Confucian official of the Shōheizaka academy, the shogunate's school, rising to the top of official learning. Specializing in Neo-Confucianism yet versed in Yōmeigaku, he was called "Zhu outside, Wang inside" by his peers, meaning he followed Zhu Xi openly while holding Wang Yangming's teaching within.
In negotiations for the Convention of Kanagawa with the United States, he assisted Hayashi Fukusai, head of the Hayashi house. Yet Yoshida Shōin wrote in a letter of his disappointment that the Hayashi and Issai disliked talk of military matters and the West. As times changed rapidly, views of Issai, who stood for traditional learning, were divided.
He died in Edo. His grave is at a temple in today's Roppongi, Minato Ward, Tokyo. Long a leading figure in learning, he raised pupils said to number three thousand, and his words survive in the Genshi Shiroku. Those he taught became a great force moving Japan from the late Edo period into Meiji.
Watanabe KazanYokoi ShōnanSakuma ShōzanSaigō TakamoriYoshida ShōinNakamura Masanao
Kobayashi IssaJippensha IkkuKyokutei BakinTakadaya KaheiHirata AtsutaneZusho HirosatoMamiya RinzōRai San'yō
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.