In music, an invention is a short composition (usually for a keyboard instrument) with two or three part counterpoint. (Inventions with three part counterpoints used to be known as sinfonias, but modern publishers are increasingly calling them "Three-Part Inventions.") The most famous are those composed by Johann Sebastian Bach. Inventions are usually not performed publically, but serve as exercises for keyboard students.

Form

Inventions are similar in style to a fugue, though much, much simpler. They consist of a short exposition, a longer development, and a short recapitulation (if there is one at all).

Exposition

In the exposition, a short motif is introduced by one voice in the tonic key. This is called the theme. The subject is then repeated in the second voice in the dominant key while the initial voice either plays a countersubject or plays in free counterpoint.

Development

The development comprises the bulk of the piece. Here the composer usually writes in free counterpoint and develops the subject by writing variations either melodically or harmonically.

Some melodic variations consist of:

• Augmentation- Playing the subject at a longer time value.
• Diminuation- Playing the subject at a shorter time value.
• Inversion- Playing a melody upside-down.
• Retrograde- Playing a melody backwards.

The development of an invention differs from that of a fugue in that a fugual development contains episodes (variations based more strictly on the theme) whereas the invention is more free-form.

Recapitulation

If an invention does have any recapitulation at all, it tends to be extremely short- sometimes only two or four measures. The composer repeats the theme in the upper voice and the piece ends. The repitition of the theme contains very little variation (or no variation at all) on the original theme. The lower line usually plays the countersubject, and if there is no countersubject, plays in free counterpoint.

History

The invention is primarily a work of Johann Sebastian Bach. Inventions originated from contrapuntal improvisations in Italy, especially from the form of the composer Francesco Antonio Bonporti. Bach adapted and modified the form to what is considered to be a formal invention. Bach wrote 15 inventions as exercises for his son, Wilhelm Friedemann Bach. These are the most well-known of all inventions. Bach later wrote another set of 15 sinfonias (three-part inventions).

Links

Inventions of J.S.Bach in Mutopia project (free sheet music)

Another site to find inventions of J.S.Bach is Sheet Music Archive

A short overview at the Northern Arizona University Website