Two-Part Invention No. 4 (D minor, BWV 775)

Background

For Bach's pupils the Inventions were often the first step. An account handed down by the son of Heinrich Nicolaus Gerber, who studied with Bach in Leipzig in the 1720s, says that Bach began Gerber's lessons with the Inventions, then moved on to his suites and finally The Well-Tempered Clavier. Short as they are, these pieces demand real independence between the hands.

The D minor Invention, BWV 775, is No. 4 of the fifteen and one of the most dramatic. It is built from a single gesture heard in the first two bars: a scale that runs up six notes to B flat, plunges down to C sharp (an awkward-sounding leap called a diminished seventh), then springs back to B flat and runs down again. The left hand soon copies it, and Bach passes it between the hands and through new keys for the rest of the piece.

The piece is in 3/8, three eighth notes to the bar, which gives it the feel of a quick dance with one beat per bar. It also has two long pedal points, where one hand holds a single note for several bars while the other keeps running, building tension before the music moves on.

How to practise it

The Invention has 52 bars. The right hand starts alone:

This fingering passes the thumb under once on the way up, then lands the thumb on C sharp so that the whole descent from B flat lies under the hand (5-4-3-2-1). Practise the drop to C sharp and the spring back to B flat on their own until they are sure.

In bar 3 the left hand takes over the motif an octave lower, while the right hand plays a broken chord in eighth notes:

Watch for the pedal points. From bar 19 the right hand holds a C for more than three bars while the left hand runs underneath, and from bar 29 the left hand holds an E for over five bars. Keep the held finger still on its key, count the bars aloud, and don't let the running hand slow down.

A plan:

1. Each hand alone in four-bar sections, with the fingering written in.
2. Hands together, four bars at a time, very slowly.
3. Join the sections, making sure every return of the motif sounds clearly in whichever hand has it.

Set the metronome to click once per bar (the dotted-quarter beat): 32, then 40, 48 and the full 56, which the app shows as 84 quarter notes a minute. In 3/8 it is easy to rush, so keep that one-in-a-bar pulse steady.

Listen for drama without heaviness: light, even sixteenths, a slight lift at the top of each scale, and a clear arrival at the final D.

The Invention No. 1 page explains how Bach collected these pieces and why.