He was born in Aizu, Mutsu Province, a son of the masterless samurai Yamaga Sadamochi, who had come from Shirakawa and lived under the protection of the Machino, senior retainers of Aizu. Soko revered his father and later wrote that nothing pained him more in exile than being unable to visit his father's grave.
As a small child he moved to Edo with his family. Edo was a new city, recently made the shogun's seat, where warriors and scholars gathered from everywhere. For the son of a masterless samurai, learning was the way to open a future.
While still a child he entered the school of Hayashi Razan, the Confucian scholar serving the shogunate, and studied Neo-Confucianism. He is said to have shown talent early and mastered Chinese classics. The knowledge he gained then later became the basis for his criticism of Neo-Confucianism itself.
From his mid-teens he studied military science under Obata Kagenori of the Koshu school and his disciple Hojo Ujinaga, and broadened his learning to Shinto and waka poetry. Combining Confucianism with military science became the pillar of his thought on how warriors should live in an age of peace.
He was invited to serve Asano Naganao, lord of Ako in Harima, but stayed in Ako only about seven months and spent most of his time in Edo. One theory says he advised on the layout of Ako Castle during its construction, but this conflicts with his own diary, and views differ.
Dissatisfied with his treatment, he resigned from Ako and became a masterless scholar in Edo. He wrote of himself after leaving the Asano as a dragon leaping from a pond into the open sea. From then on he taught military science to many daimyo and warriors in Edo, and his fame as a scholar grew.
Having begun to doubt Neo-Confucianism a few years earlier, Soko argued for returning directly to the teachings of Confucius and wrote the Seikyo Yoroku. Valuing practical learning useful in daily life over abstract debate, it made him a pioneer of what came to be called Ancient Learning.
Because the Seikyo Yoroku criticized the Neo-Confucianism favored by the shogunate, he was summoned by the inspector general Hojo Ujinaga, once his own teacher, and ordered into exile in Ako. There he lived in a corner of the residence of the Oishi, a family of domain elders, and though his diary records his despair, he kept writing.
In exile he wrote the Chucho Jijitsu, arguing against the view that China was the center of the world and claiming that Japan was the true central realm. He also wrote the Buke Jiki, a history of the warrior houses, in this period, widening the range of his scholarship.
After about nine years of exile he was pardoned and returned to Edo. His diary says the first lord he met after his pardon was Kira Yoshinaka, and he expressed his joy in a Chinese poem. The Ako ronin later avenged their lord, but Soko's link with that affair is thought to have been emphasized by later generations.
He named his Edo home Sekitokudo and taught the Yamaga school there, supported by the Tsugaru of Hirosaki and the Matsura of Hirado. This year he presented the Chucho Jijitsu to Tsugaru Nobumasa and later gave him the Yamaga military-science certificate. His sons went on to serve these two houses.
He fell ill in summer and was visited by Matsura Shigenobu of Hirado and members of the Tsugaru house, but died in Edo that autumn at 63. His grave is at Sosanji in Ushigome. The Yamaga school of military science was handed down in many domains, and in the late Edo period Yoshida Shoin of Choshu studied it.
Hayashi RazanYoshida ShōinŌishi Kuranosuke (Yoshio)
Kawamura ZuikenKumazawa BanzanAmakusa ShirōMitsui TakatoshiSakai TadakiyoItō JinsaiTokugawa MitsukuniKaibara Ekiken
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.