He was born in the castle town of Mito, the eldest son of the Mito retainer Aizawa Yasutaka. The Aizawa had been farmers in Kuji District who rose from catching small birds for the lord's falconry, and only in his father's generation did the family attain samurai status. The atmosphere of a family that had climbed by effort nurtured his zeal for learning.
At about ten he entered the private school of the young scholar Fujita Yūkoku and was praised as calm, deep and of outstanding insight. Yūkoku was only about eight years older but already famed for his learning, and he valued practical scholarship useful to society over empty theory. Seishisai revered this teacher all his life and later recorded his teachings in a book.
He entered the Shōkōkan, the office compiling the Dai Nihonshi, the history the Mito domain had worked on for generations, as a copyist. Around this time a Russian envoy had come to Nemuro, and his teacher Yūkoku grew concerned about Russia's southward advance, so Seishisai too began studying Russia from whatever books he could find.
From his research he wrote Chishima Ibun, describing Russia and international relations in the north. At a time when few knew anything of foreign countries, his concern for Japan's northern defense was unusual. Preparing for threats from abroad became a pillar of his scholarship from this time on.
He was appointed tutor to the lord's sons, among them Tokugawa Nariaki, later the ninth lord. The trust forged with Nariaki through study became the basis for their later work together on domain reform. He is said to have earnestly taught the young lord the spirit of defending the country and the lessons of history.
English whalers landed at Ōtsuhama in the Mito domain seeking food. Though he spoke neither English nor Dutch, he questioned them about their voyage by showing world maps and writing numbers, and wrote up a record. This actual appearance of foreign ships on Japan's shore heightened his sense of crisis.
After the shogunate ordered foreign ships driven off, he wrote the Shinron, arguing how to face crises within and without, and presented it to the lord. It set out systematically the sonnō jōi idea of uniting the country around the emperor and repelling foreigners, but because it touched on shogunate policy it long went unpublished.
When a succession dispute arose, he joined Fujita Tōko and others in backing Nariaki and hurried to Edo. He was confined for going to Edo without leave but soon pardoned. When Nariaki became lord, Seishisai was given heavy responsibilities, became head of the Shōkōkan compiling the Dai Nihonshi, and supported domain reform.
He was appointed the first head professor of the Kōdōkan, the domain school founded by Nariaki. Before it opened he studied the size and teaching of domain schools across the country and wrote a book on school organization. The Kōdōkan opened the next year as a place for both letters and arms and became a base for spreading Mito learning among retainers.
When Nariaki was censured for his reforms and ordered by the shogunate into retirement and confinement, Seishisai too was ordered to stay shut in his house. Four years later, when Nariaki returned to politics, he was pardoned and taught again at the Kōdōkan. He even had an audience with the shogun, and his name as a scholar became known nationwide.
Yoshida Shōin of Chōshū visited Mito and met Seishisai six times to learn from him. Seishisai is said to have entertained him with sake and shared his broad knowledge of the affairs of the realm. Through this encounter Shōin grew more conscious of Japan as a nation. The Shinron came to be widely read by the activists of the late Edo period.
When the shogunate signed commercial treaties without the court's approval, the court sent a secret edict to the Mito domain. Seishisai opposed passing it on to other domains and argued it should be returned to the court, clashing with radical sonnō jōi activists. When Nariaki was punished in the Ansei Purge and the domain fell into turmoil, he worked hard to restore order.
He presented Hitotsubashi Yoshinobu with Jimusaku, arguing that under present conditions intercourse with foreign countries was unavoidable. This realistic view from a man regarded as a master of expulsionist thought drew scorn from radicals, who called him senile. It was a conclusion reached by watching the times change rather than clinging to the views of his youth.
He ended his long life of over eighty years at his home in Mito. Phrases from the Shinron were partly adopted by late Edo activists and influenced the ideas of the state after the Meiji period. On the other hand, his late acceptance of opening the country was taken by some as a betrayal of principle, and views of him remain divided today.
Tokugawa NariakiFujita TokoYoshida Shōin
Zusho HirosatoMamiya RinzōRai San'yōHirose TansoNinomiya SontokuŌshio HeihachirōWatanabe KazanMizuno Tadakuni
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.