The pedal point

A bass tone — almost always the tonic or the dominant — is sustained while the upper voices move through harmonies by turns consonant and dissonant against it. The license has two conditions: the pedal must enter and leave as a consonance, and the upper voices must be well formed among themselves, as if the pedal were not there. It is licensed at all because the held tone is the key’s anchor — the ear files everything above it as motion over a ground.

A pedal prolongs a single harmonic function across many bars: fixing the bass on tonic or dominant lets the upper voices run a real progression above it, keeping the passage moving while the ear never drifts from home. It suits a piece that must assert a key beyond argument — an extended close, a cadence’s approach — because the held tone licenses dissonances the harmony could not otherwise support on its own. A dominant pedal builds suspense; a tonic pedal builds confirmation, holding a close open past when it could have ended.

• Letting the pedal itself enter or leave as a dissonance, which breaks the one condition that makes everything sounding against it legible as motion over a ground.
• Writing the upper voices carelessly on the theory that the pedal excuses anything above it, when the license requires those voices to be well formed among themselves.
• Holding the pedal so long that the harmony above stops implying any real progression, so the ear stops crediting the upper voices with motion.
• Choosing a scale degree other than the tonic or dominant for the pedal without strong reason, which weakens the sense of anchor the whole effect depends on.
• Releasing the pedal into a vague or unprepared harmony, so the moment it lets go is exactly where the passage most needs the clarity the pedal was building toward.

• Ebenezer Prout, Harmony: Its Theory and Practice (1889), The chapter on pedals — The conditions of the license: consonant entry and exit, upper voices correct among themselves.
• Johann Georg Albrechtsberger, Gründliche Anweisung zur Composition (1790), The chapter on the organ point — The strict-composition account of the Orgelpunkt at the close of fugal writing.
• George Frideric Handel, Thoroughbass and composition lessons for Princess Anne (1724), The thoroughbass lessons, pedal-point exercises — Handel sets the device as a keyboard exercise: changing figures over the held bass.