Invention

Short contrapuntal studies Bach wrote for students, one motif carrying the whole piece

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An invention is a short contrapuntal piece Bach wrote for keyboard students, one motif carrying the whole thing, usually a single page long.

Origins and era

In the 1720s, at Köthen, Bach wrote keyboard pieces for his eldest son Wilhelm Friedemann, first titled praeambula and fantasias and later renamed inventions and sinfonias. Fifteen two-part and fifteen three-part pieces are ordered by key, running from C major to B minor. Italian ricercars and German fantasias had used similar writing before, but Bach cut the length to a page and fixed the method. Ever since, the invention has been the entry point to contrapuntal teaching, and almost every keyboard player passes through it.

What you hear

One movement of a minute or two, with a short motif threading the whole piece. A two-part invention has only two lines, the subject stated in the first voice then imitated at once by the second in the dominant, the middle developed by sequence and modulation, the close returning to the tonic. A three-part invention adds a middle voice, the texture thickens, the harmony fills out, and the subject often enters after a rest that opens a gap. Memorise the first three or four notes, count how often they return, and note the key and voice of each entry. In the two-part pieces the subject usually appears once in full, the other voice answers in the dominant, sequences carry the key to a neighbour, and the close returns to the tonic, a route that can be retold for every one of them. The three-part versions also invert or augment the subject, so a familiar outline keeps changing shape.

Key figures

Bach is the centre of the genre, since his two- and three-part inventions set its length and method. Twentieth-century teaching still uses these thirty pieces as an introduction to counterpoint, and composers occasionally borrow the title as homage.

Lineage

It grows from the imitative writing of the ricercar and fantasia and leads to the fugue, the three-part invention and twentieth-century keyboard studies.

Common misunderstandings

An invention is not free improvisation, because every piece has a strict plan of imitation and key. Nor is it only child's practice, since the voice-leading of the three-part inventions already prepares for the fugue.

Sources

• The New Grove Dictionary of Music and Musicians, 2nd ed., entry Invention, 用于核对创作年代与教学用途
• Christoph Wolff, Johann Sebastian Bach, The Learned Musician, 用于核对克滕时期的键盘教材背景

Used for fact-checking only; all prose is original.