琴瑟 (qín sè) — Qin and Se in Tune · Marital Accord as Shared Music · Two Instruments, One Music

The Ministry of Education's revised dictionary opens on the instruments: 琴与瑟两种乐器. 《书经·益稷》 has them under the hands that lift the song — 搏拊琴瑟，以咏 — and 《周礼·春官·大司乐》 places 云和之琴瑟 inside the dance of 云门. Before the word means a marriage, it means two string instruments that belong in the same music.

The marriage reading is borrowed, and the dictionary says so. Sense two is 语本《诗经·小雅·常棣》: 妻子好合，如鼓瑟琴 — a household in good union is like playing the se and the qin. 《关雎》 had already put the same two instruments beside courtship — 琴瑟友之 — and 《女曰鸡鸣》 had put them in the house — 琴瑟在御. Those lines are already quoted elsewhere in this library; what they leave for this entry is the compact headword. Once the metaphor sticks, the negative proves the positive: 琴瑟不调 is marital discord, and Dong Zhongshu can steal the same image for bad government because everyone already knows what in-tune strings are supposed to do.

The two instruments are not the same voice. Traditional accounts give the qin five strings in early Zhou use, later seven; the se is the larger zither, later fixed in the received tradition at twenty-five strings, each with its own movable bridge. 琴瑟和鸣 is still the standing four-character wish for a marriage whose parts answer each other without becoming one instrument.

At a Chinese wedding the toast may still land on 琴瑟和鸣 or 琴瑟之好 — not a claim about how much anyone feels tonight, but a picture of two registers playing together. The gift copy that follows that toast is doing the same work: it names the ensemble, not the solo.

The word also keeps a repair story. When the Hanshu has Dong Zhongshu say that badly tuned 琴瑟 must be loosened and restrung before they can be played again, the political analogy only works because the domestic one is already clear. A marriage that has gone sharp or flat is still being talked about in the language of strings.