Cantus Firmus

About

Bach set the same Lutheran hymn tunes over and over. A melody that opens a cantata in 1724 comes back as a four-part harmonisation, and again under an organist's hands, and again in a Passion. Those borrowed tunes are the cantus firmus — the fixed song a composer builds around — and they are the hidden wiring of the catalogue. This is a map of them, made for the phone. Open a work and you get its movements, with type, key and scoring. Where a movement sets a chorale melody, a chain-link icon says how many other works set the same one. Tap it and there they are, grouped by the tune they share — so a connection reads as a fact about the music rather than a line on a graph. THE CATALOGUE • 554 works — cantatas, motets, the two Passions, the Christmas Oratorio, four-part chorales, organ chorales, concertos • 1,940 movements • 209 chorale melodies, each with its Zahn number and every place Bach set it • 1,554 connections, worked out in advance, so following one is instant • Search by BWV number or by text, across titles, occasions and sung incipits TODAY The app opens on what Bach wrote around this date, and separately on the works for the coming Sunday in the church year. The two are labelled apart deliberately: most of these feasts were movable, so a premiere anniversary and a liturgical occasion fall on different days, and merging them would be a small lie. LISTENING 1,509 movements have a synthesised rendering that streams on demand. 1,956 recordings on Apple Music are matched to a work or a movement, covering 532 of the 554, and play in place if you subscribe. If the work is already in your library, the app finds your own recordings and marks them with a heart. It never chooses for you — both are offered, and each control says what it will play. THE WORDS The sung text in German with the English beneath it, interlinear where the translator set it that way. Every translation is credited to its translator on the page it appears on. 250 works have their text; most of the rest are organ chorales, which have none. COMMENTARY A paragraph on each of 159 cantatas, written by whichbachcantata.be and used with its author's kind permission, each naming and linking the essay it came from. YOUR OWN NOTES Write a note on any work or movement, or correct the catalogue where it is wrong. Both live in a file of their own on the phone, and a catalogue update never overwrites them. A QUIZ Five kinds of round, including listening questions that play a phrase and ask you to name it. No account, no advertising, no analytics, nothing collected about you. The whole catalogue ships inside the app and works offline; only the recordings need a connection. The catalogue has gaps and says where they are — a movement without a title, a work without a recording. Corrections are welcome, and the About screen is the way to send one.