Invention

One idea, two voices

The word goes back to Latin “inventio”, “invention”. What is meant is the musical idea, the theme from which the whole piece grows. An invention is a small keyboard piece in two or three voices, written in imitative counterpoint. In Bach the inventions have two voices; the pieces he calls “Sinfonias” have three.

Imitation on the page

One way of working out the theme is imitation: what one voice has played, the other voice takes up shortly afterwards, often at a different pitch. On the page you can see it in the rests. One voice enters, the other waits and begins later with the same figure. In the three examples from the archive this happens differently each time: in No. 1 the lower part answers already in the second half of the first bar, in No. 3 at the end of the second bar, in No. 4 only in the third bar.

Two-part inventions by Bach

• Invention Nr. 1 C-Dur Johann Sebastian Bach, BWV 772, from: Two-Part Inventions · piano · 2 pages

  Two staves, treble clef for the right hand and bass clef for the left, time signature C, no key signature. The upper voice begins with a sixteenth rest and seven sixteenth notes; in the second half of bar 1 the lower voice plays the same rhythmic figure an octave lower. The piece ends in bar 22 with a chord that has a fermata and an arpeggio sign.

• Invention Nr. 3 D-Dur Johann Sebastian Bach, BWV 774, from: Two-Part Inventions · piano · 2 pages

  Time signature 3/8, two sharps, an upbeat of two sixteenth notes. The lower voice rests at first, enters at the end of bar 2 with the same upbeat and plays the figure from bars 1 and 2 in bars 3 and 4.

• Invention Nr. 4 d-moll Johann Sebastian Bach, BWV 775, from: Two-Part Inventions · piano · 2 pages

  Time signature 3/8, one ♭ in the key signature; the title gives the key in the German form “d-moll”. The upper voice begins with six rising sixteenth notes in the first bar; the lower voice rests in bars 1 and 2 and enters in bar 3 with this figure an octave lower.

Invention and symphony

In Bach the three-voice pieces of this kind are called “Sinfonias”; some editions call them “Three-Part Inventions” so that they are not confused with the symphony for orchestra. The archive holds three pieces from the “Two-Part Inventions”, where the number of voices is already in the title. Invention No. 1 has 22 bars.

Common mistakes

• Hearing only the melody: In an invention every voice has equal weight; when the figure appears in the lower voice, it deserves your attention.
• Playing the figure differently in the second voice than in the first: To keep the imitation audible, it helps to have both hands articulate the figure in the same way.
• Equating invention with an invention in the everyday sense: Here the word means a piece and the way it is written, not just any new thing.