Level 2 · Course 40

The Two-Voice Invention

Subject, imitation at the octave, countersubject, episodes and tonal plan — writing the invention in Bach's style, toward the DEM counterpoint.

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Pause Culture · The two-voice invention

Johann Sebastian Bach (1685–1750)

In 1723, Johann Sebastian Bach gathered fifteen short pieces (BWV 772–786) which he called “Inventions” for the use of his pupils — foremost among them his son Wilhelm Friedemann. …

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À retenir : An invention is a motive brought to life: you state it, imitate it at the octave, develop it in episodes, and bring it back to the tonic. A single well-chosen subject is enough to build the whole piece.

The subject, the imitation and the countersubject

A two-voice invention is a contrapuntal piece in which two independent voices converse from a single motive, the subject. It is the direct ancestor of the fugue and the first step toward the Bach counterpoint required at the DEM.

The principle: all the material of the piece — melody, accompaniment, transitions — derives from a single motive. Nothing is gratuitous: every figure is a transformation of the subject or its countersubject.

The subject (generating motive)

The subject is the opening melodic motive. Its head-motive (incipit) — its first notes, its rhythm and its characteristic contour — gives the piece its recognisable identity. A good subject is short and memorable.

The imitation

The second voice repeats the subject after a short delay. Most often the imitation is at the octave (sometimes at the fifth). It is the imitation that creates the two-voice dialogue.

At the octave: the answer faithfully reproduces the subject, an octave lower (or higher). At the fifth, we approach the subject/answer principle of the fugue, but the invention most often stays at the octave.

The countersubject (free voice)

While the 2nd voice states the imitated subject, the 1st voice continues with a countersubject — a recurring melodic figure that accompanies the subject — or with a free voice. The two voices must remain genuinely independent (counterpoint).

Independence of the voices: the countersubject must not merely double the subject in chords. It converses with it: complementary rhythms, contrary motion, staggered entries. Therein lies the whole difficulty of two-voice counterpoint.