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一心同体 isshin dōtai One in Mind and Body

一心同体 (isshin dōtai), one heart, one body, is the phrase a Japanese dictionary now illustrates with husband and wife. It began in Chinese for a minister and his king, a master and disciples, and sworn brothers. This study follows it into a Tokyo police regulation of 1874 and to a married couple in a translation of 1876.

Japanese Scroll of One in Mind and Body (isshin dōtai) — Calligraphy by Eri Takase
One in Mind and Body一心同体isshin dōtai

Original art by Master Calligrapher Eri Takase

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Abstract

一心同体, isshin dōtai, one heart, one body, is a Chinese phrase for a minister and his king, a master and his disciples and sworn brothers, which Meiji Japan gave first to its police and its soldiers, then, under the Christian one flesh, to husband and wife from 1876. The older phrase for two bodies with one heart is 異体同心, bodies apart, one heart, which Nichiren made the word for his community.

Overview

The sense. One heart, one body: a Chinese phrase for a minister and his king, a master and his disciples and sworn brothers, which Meiji Japan gave first to its police and its soldiers and then, under the Christian one flesh, to husband and wife.

The words. 一心 is one heart: the Buddhist one mind, the single-mindedness of a man at prayer, and the hundred million hearts as one of a wartime proclamation. 同体 is one body: in Japanese first cited from a Buddhist text of 984 on the Buddhas' single body, and older in Chinese, in the 荘子. Together the dictionaries gloss them two or more people acting with one heart, bound like one person. 大辞泉 illustrates the phrase with husband and wife are one heart and one body, and the big dictionary's first citation is a wife saying it to her husband; the four-character dictionary's examples are a pair of lovers in 谷崎's 卍 and a speaker of 1976 who will tell people you and I are one heart and one body [1]. The Meiji spelling was often 一身, one person, rather than 一心, one heart: the big dictionary's own first citation is spelled that way and calls the spelling a mistake, and the four-character dictionary notes that in Meiji it was mostly written so. The modern 一心 is the ruling form.

The older phrase for two bodies with one heart is 異体同心, bodies apart, one heart. It is Nichiren's word for his community, and by 1905 漱石's cat could laugh at it as the old way of talking about marriage [1].

The text in English. The English of 一心同体 is one flesh, Genesis 2:24, from the 1908 idiom dictionary through 斎藤 and 武信 to the modern 研究社, and a Japanese New Testament quoted in an idiom dictionary of 1968 gives Jesus's they twain shall be one flesh (Matthew 19:5) as ふたりの者が一心同体になるのだ [2].

The historical record

Song to Qing. A Ming novel, a Song commentary, a secret society. Chinese Wikisource has 一心同體 in three kinds of text. In the 西遊記, chapter 32, the Tang monk had got Sun Wukong back, and master and disciples, one heart and one body, went on together toward the West; in the 1696 annotated edition the National Diet Library holds. A Song commentary on the 書経, 黄度's (1138–1213), says the Grand Protector and the young king were one heart and one body. And the initiation oath of the 天地會, the Heaven-and-Earth Society, as a Qing miscellany records it, runs: once in the Hong gate, be of one heart and one body, support one another, allow no distinction of you and me. The phrase names a brotherhood. The commoner Chinese phrase for the same idea, 異體同心, is older: a Tang ode on a tree whose two trunks grew into one, and a prose-poem on two yellow men guarding the sun, bodies apart and one heart, two forms joining their strength like the left and right hand, in a print of 1567. Neither is a phrase for a couple. The Chinese couple's phrase is 形影相隨, form and shadow following each other [3]. Neither Buddhist canon searchable at the line, CBETA or the Taishō at SAT, has the four characters 一心同體 [4].

1134 to 1905. The older word. The oldest Japanese uses of 異体同心 found are Buddhist and of the twelfth century. 三善為康, who died in 1139, tells in his lives of those reborn in the Pure Land of a nun who in 1134 asked her two daughters to have a Buddha made with the red beans she had counted her prayers on: the daughters, hearing this, took the clothes from their backs and the food from their mouths and, bodies apart and one heart, had made a sixteen-inch Amida [5]. A Shingon ritual book of the same century, 實運's 祕藏金寶鈔, asks the deities of the mandala to lend their power with bodies apart and one heart [6]. Nichiren's letter written of the believers at Atsuhara carries the day and not the year, and both its year and the person it went to are argued over: an English edition gives a lay follower, Takahashi Nyūdō, and a date between 1275 and 1280, the tradition 1279, the year of the persecution there, and two Nichiren scholars have disputed the year and the addressee in print since 2017 [7]. It says: with bodies apart and one heart every thing is achieved; with one body and hearts apart nothing is accomplished — so it stands in three thousand volumes of the outer canon. King Zhou of Yin had seven hundred thousand horse but hearts apart, and lost; King Wu of Zhou had eight hundred men but one heart, and won. Another letter makes it the definition of his community: all my disciples and patrons, with no thought of self and other, as fish think of water, chanting the daimoku with bodies apart and one heart — that is the lifeblood. Four monks who printed a Buddhist chronicle in 1612 signed their colophon four monks gathered, bodies apart and one heart, cut the blocks. This is the word the cat remembers in 1905: in the old days there was no argument; they said 異体同心, and though you saw two people you had in fact one; and so they called it "old together, one grave," and even dead turned into badgers in one hole. Barbarous. [8]

1874: the police. The oldest dated Japanese use of 一心同体 known is a Tokyo police regulation of the seventh day of the second month of 1874, printed with its date in a police handbook of 1878: Article 3. Those on duty together shall consider themselves one heart and one body, make mildness and gentleness their rule, do their duty to one another with sincerity, and encourage one another not to slacken. The same year 西郷隆盛 wrote, in Chinese, a memorial for the volunteers who died in the Taiwan expedition: in our levied company we were one heart and one body, as when the right hand is in trouble the left hand answers without thinking. In 1877 a translator of Rousseau used it for the social contract's single body: when many men gathered together regard themselves as one heart and one body. In 1880 a translated church history had Francis Xavier write to a friend, my soul is your soul and your heart is my heart, truly a feeling of one heart and one body. Through the 1870s and 1880s the phrase belongs to the state, the army, the church and the philosophers, and the commentaries on the emperor's rescript to soldiers gloss his limbs and head with it [9].

1876: the couple, under "one flesh." The first use for husband and wife known is in 永峰秀樹's abridged translation of an American book on household economy, by one Haskell, of December 1876: the husband, toward his wife, hiding nothing in anything, truly puts the phrase "one body" into practice (spelled 一身, one person; as the Library's index text has it, the book being open only in Japan) [10]. In the Genrōin, the appointed chamber that reviewed the laws, on 9 December 1881, a councillor argued that the husband should be his wife's legal guardian because the two are one body (spelled 一身, one person), the wife being among the legally incapable, and that the rule was needed now to prevent the false doctrine of the equal rights of men and women [11]. Two years later a Tokyo debating society argued over whether to hold husband and wife one body, which is of old the religious teaching of the European countries, stood to reason (as the Library's machine-read text has it; the page images are not served) [11]. The Orthodox Church's catechism of 1883 put it into the sacrament of marriage: that they may obtain the grace to bear and raise children in a pure one-heart-one-body. The novels follow: a political novel of 1887, in which a wife asks her husband is it not said that husband and wife are one body? and the two later felt ever more one body and one heart, their love doubled from the day before (spelled one person); a novel of 1891, the two grew ever closer, the one-heart-one-body of the mountain; a conduct book of 1899, the couple's affection was enviable to onlookers, always as if one heart and one body. 福沢諭吉's New Greater Learning for Women of the same year makes it the marriage contract's clause and then limits it: husband and wife being one heart and one body, the contract to share pain and pleasure may not be broken at the cost of life; yet apart from the division of household labor into inner and outer, there is no rank of high and low between them, and each should hold to equality in all things. In 1908 an English idiom dictionary printed the equation: She and I are one flesh — 一心同体だ, with (husband and wife) in brackets. 斎藤秀三郎's English-Japanese dictionary of 1915 gave to be (or become) one flesh as 一身同體(夫婦)と成る and second self as 一心同體の友 [12], and 武信's Japanese-English dictionary of 1918 has to become one flesh and, for a friend, one's second self. By 1910 the proverb dictionary lists husband and wife are one heart and one body among the sayings on marriage, and the 1919 national dictionary files it under 夫婦 as a proverb. In the National Diet Library's open full-text index the count of books goes from eighteen in the 1870s to nearly a thousand in the 1930s [13].

The sense across time. 一心同体 kept one sense, many acting as one, and changed its subject: a minister and his king, disciples and brothers in China, police and soldiers and a nation in Meiji Japan, the couple from 1876 on. 大辞泉 now illustrates it with the couple, as if it had always been theirs.

What is not a source. 一心同体 is not an old Japanese saying about marriage: it entered Japanese in 1874, and was first said of a couple in 1876.

Today. The open dictionary glosses 一心同体 being one in body and soul; of one flesh; two hearts beating as one [14]; one's second self, for a friend, is in the English-Japanese dictionaries from 1915 [12]. In the article titles CiNii indexes from 1953 on it is said of couples, and as readily of a prime minister and his secretary, a firm and its suppliers, a team and its supporters, a mother and her son [15]; an idiom dictionary of 1968 uses it of a team at work, and one of 2002 gives both when they say man and wife are of one heart and mind and we're one and the same, you and me [2].

A reading

一心同体 is the word a Japanese dictionary gives for a couple today, and it is said as readily of any two who act as one. It came from a Song commentary's minister and king, a Ming novel's master and disciples, a police regulation of 1874, Saigō's volunteers, and the European one flesh by which it became a marriage word in 1876. One heart, one body is the literal; of one flesh is what a Japanese reader hears. The older Japanese word for two bodies and one heart is 異体同心, which Nichiren made his community's.

References

  1. 「一心」・「同体」・「一心同体」・「異体同心」, 精選版日本国語大辞典・デジタル大辞泉・字通, at kotobank. https://kotobank.jp/word/一心同体
  2. Charles Corwin, A Dictionary of Japanese and English Idiomatic Equivalents, Kodansha International, 1968, under KYŌRYOKU and KEKKON (the Matthew 19:5 rendering, its translation not named there); Taeko Garrison, Kodansha's Dictionary of Basic Japanese Idioms, Kodansha International, 2002, isshin-dōtai.
  3. 西遊記, ch. 32 (吳承恩), in 陳士斌 (annot.), 西遊眞詮, 1696 print, scan 38; 黄度, 尚書說, 卷7 (Song; 四庫全書本); 清稗類鈔, 070 (the 天地會 oath); 文苑英華, 卷2, 1567 print, scan 166 (異體同心); at zh.wikisource and NDL Digital Collections. https://dl.ndl.go.jp/pid/2566696/1/38
  4. CBETA, the full text, 一心同體 and 一心同体, no hits; SAT 大正新脩大藏經テキストデータベース, 一心同體, no hits (1 October 2026). https://cbdata.dila.edu.tw/stable/search?q=一心同體 · https://21dzk.l.u-tokyo.ac.jp/SAT/ddb-sat2.php?key=一心同體&mode=search
  5. 三善為康, 後拾遺往生伝, 巻下 (written up to 1139), in 続群書類従, manuscript, National Diet Library Digital Collections, scan 56. https://dl.ndl.go.jp/pid/2553889/1/56
  6. 實運, 祕藏金寶鈔, T2485, vol. 78, 0366c20, at SAT. https://21dzk.l.u-tokyo.ac.jp/SAT/T2485_.78.0366c16:0366c29.cit
  7. Philip B. Yampolsky (ed.), Selected Writings of Nichiren, Columbia University Press, 1990, pp. 352–353, On Itai Doshin, the introduction; 川﨑弘志, in 法華仏教研究 (2017, 2019), and 榎木境道, in 日蓮正宗教学研鑽所紀要 (2018, 2020, 2022), on the letter's year and addressee, listed at CiNii and not open. https://cir.nii.ac.jp/crid/1520573330486317568
  8. 日蓮, 異体同心事, in 日蓮上人御遺文, 1904, scan 543; 生死一大事血脈抄, in 日蓮大士言行録, 1915, scan 66; 佛祖歴代通載, colophon, 1612, National Diet Library Digital Collections; 夏目漱石, 吾輩は猫である, 1905–06, at ja.wikisource. https://dl.ndl.go.jp/pid/823848/1/543 · https://dl.ndl.go.jp/pid/953296/1/66
  9. 警視庁, 巡査心得, 1874, in 警察類聚, 1878, scan 22, and 東京警吏須知, 1878, scan 8, and 本朝民鑑, 1877, scan 416; 西郷隆盛, 祭臺灣戰死者文, in 南洲遺稿, 1877, scan 14; 服部徳 (trans.), 民約論 (Rousseau), 1877, scan 142; 日本西教史 (Crasset, trans.), 1880, scan 661. https://dl.ndl.go.jp/pid/790973/1/22 · https://dl.ndl.go.jp/pid/894346/1/14 · https://dl.ndl.go.jp/pid/783743/1/142 · https://dl.ndl.go.jp/pid/824974/1/661
  10. ハスケル (Haskell), 家政要旨 : 経済小学, 永峰秀樹 (abridged trans.), 内藤伝右衛門, December 1876, and its edition of November 1877; National Diet Library Digital Collections, the full-text index (the images are open in Japan only). https://dl.ndl.go.jp/pid/848296 · https://dl.ndl.go.jp/pid/903980
  11. 元老院会議筆記, 9 December 1881, 第二百七十八號議案 (治罪法 on the legally incapable), National Diet Library Digital Collections, scan 509; 国友叢談 (国友会, ed. 田中岩三郎, 1883), scan 33, the machine-read text. https://dl.ndl.go.jp/pid/1367161/1/509 · https://dl.ndl.go.jp/pid/783084/1/33
  12. 斎藤秀三郎, Saito's Idiomological English-Japanese Dictionary (熟語本位英和中辞典), 1915, under Flesh, Alter ego and Second; the 1918 printing, scan 590, p. 1165. https://dl.ndl.go.jp/pid/1681530/1/590
  13. 初実の果, 正教会, 1883, scan 137; 末広鉄腸, 花間鶯, 上編 (1887), in the 1888 edition, scans 87 and 96; 花守, 金港堂, 1891, scan 69; 家庭の鑑, 国光社, 1899, scan 27; 福沢諭吉, 新女大学, 1899, at ja.wikisource; 英和熟語慣用句辞典, 三省堂, 1908, scan 157; 武信, 武信和英大辞典, 1918, scan 331; 諺語大辞典, 1910, scan 459; 大日本国語辞典, 1919, scan 246. https://dl.ndl.go.jp/pid/824573/1/137 · https://dl.ndl.go.jp/pid/885846/1/96 · https://dl.ndl.go.jp/pid/887832/1/69 · https://dl.ndl.go.jp/pid/848330/1/27 · https://dl.ndl.go.jp/pid/870072/1/157 · https://dl.ndl.go.jp/pid/925665/1/331
  14. JMdict (EDRDG), 「一心同体」, at jisho. https://jisho.org/word/一心同体
  15. CiNii Research, article titles on 一心同体, 72 records, 1953–2026 (1 October 2026). https://cir.nii.ac.jp/all?q=一心同体

Authors

Tim Jackowski (Systems Architect, Takase Studios, LLC) · 典 Ten (Anthropic Claude Fable 5.1, Takase Studios, LLC)

AI written · Ten wrote the history. Tim Jackowski commissioned it and answers for it.

Checked · Claude Sonnet (Anthropic), 2026-09-15, citations — every claim tested at its address; most verbatim; one gloss the record called verbatim is actually reordered, now corrected; the rest not openable, page images all opened by hand

Cite as: Tim Jackowski and Ten, "Philology of 一心同体 (isshin dōtai)," Takase Studios, 2026, https://takase.com/library/philology/isshin-dotai.