Questions: Voice Leading in Authentic and Plagal Cadences

Question 1

In a perfect authentic cadence in C major (V→I), the leading tone B appears in the alto voice. What must happen to this B?

• A. B moves down to G to create smooth voice leading and avoid doubling issues
• B. B moves up to C, even if this means the tonic chord ends with a doubled third
• C. B sustains as a common tone, since B is present in both the V and the following chord
• D. B moves down to E to provide the third of the tonic triad

Answer: (B)

The leading tone's upward resolution to tonic is obligatory in an authentic cadence — it is the defining voice-leading event of the V-I motion. B is not a common tone (it does not appear in C major's I chord), so sustaining it is impossible. Moving down to G or E abandons the semitone pull that gives the authentic cadence its sense of closure. If the mandatory B→C resolution means the tonic chord ends with a doubled third (E) rather than a doubled root, that doubling is accepted as a necessary consequence.

Question 2

Which quality most fundamentally distinguishes a plagal cadence from a perfect authentic cadence?

• A. The plagal cadence uses a minor iv chord, giving it a darker, more ambiguous sound
• B. The plagal cadence lacks the leading tone, so there is no semitone pull creating urgency — resolution feels gentle and settled
• C. The plagal cadence resolves to the dominant rather than returning to the tonic
• D. The plagal cadence occurs only at the beginning of phrases as a point of departure

Answer: (B)

The core difference is the leading tone. In V-I, the seventh scale degree (a half step below tonic) creates intense upward pressure that resolves with urgency. IV contains no leading tone: the motion from IV to I involves whole-step and common-tone motion with no semitone pull. This is why plagal cadences sound settled and hymnal rather than conclusive and directed. Option A is incorrect because the plagal cadence can use major IV as well.

Question 3

In an authentic cadence, if the leading tone appears in an inner voice rather than the soprano, its upward resolution to tonic can be omitted to create a smoother voice leading.

• T. True
• F. False

Answer: False

The leading tone's upward resolution is obligatory regardless of which voice carries it. There is no exception based on register or voice placement. Even if resolving B up to C in the alto creates an awkward leap elsewhere or results in a doubled third in the tonic chord, the resolution must still occur. The leading tone's role in creating cadential closure is so fundamental that departing from it weakens the cadence significantly.

Question 4

Plagal cadences often appear after an authentic cadence because they provide a final, gentle layer of closure to a phrase that has already formally ended.

• T. True
• F. False

Answer: True

Because the plagal cadence does not have the driving urgency of V-I, it rarely functions as the primary cadential arrival by itself. Instead, it commonly follows a perfect authentic cadence as a kind of 'amen' — adding a soft, harmonically stable confirmation of tonic after the formal close has already been achieved. This usage is especially common in hymns and choral music, where the plagal 'amen' became a convention precisely because of its settled, non-urgent character.

Question 5

Why does the leading tone resolution feel nearly inevitable in an authentic cadence, and what happens to this sense of urgency in a plagal cadence?

Model answer: The leading tone is a semitone below the tonic, creating intense acoustic and psychological tension. The half-step interval has the smallest possible distance to resolve, making the upward pull feel almost mechanical. In a plagal cadence (IV→I), the chord contains no leading tone — the fourth scale degree moves down by whole step to the third of the tonic, and other voices move smoothly or hold common tones. Without the semitone pull, there is no urgency, no sense of arrival forced by acoustic pressure. The resolution is harmonically stable but not tonally directed.

This voice-leading difference explains the emotional contrast: authentic cadences arrive with a sense of finality and release of tension (the leading tone 'snaps' into place), while plagal cadences settle without drama. Composers exploit this contrast intentionally — using authentic cadences for structural arrivals and plagal cadences for gentle, lyrical closes or post-cadential extensions.