Cadential 6/4 Chords in AP Music Theory: A Complete Guide

What Is a Cadential 6/4 Chord?

Cadential 6/4 chord (pronounced “six-four”) is a common harmonic device used in classical and tonal music to create a strong, delayed resolution to the dominant (V) chord. It is a type of second inversion tonic chord (I⁶₄) that embellishes the dominant, adding tension before the final cadence.

Why Is It Called “6/4”?

The numbers 6/4 refer to the intervals above the bass note:

  • 6 = a sixth above the bass
  • 4 = a fourth above the bass

In a I⁶₄ chord, the bass note is the 5th scale degree (sol), while the upper voices form a tonic triad (do-mi-sol).


How to Identify a Cadential 6/4 Chord

  1. Occurs Before the Dominant (V) – It always resolves to V (or V7).
  2. Bass Note is Scale Degree 5 (Sol) – The chord is in second inversion.
  3. Part of a Cadential Progression – Typically found at the end of a phrase (e.g., I⁶₄ → V → I).

Example in C Major:

  • Cadential 6/4: G (bass) + C-E-G (upper voices) = I⁶₄
  • Resolution: Moves to V (G-B-D) then I (C-E-G)

Voice Leading Rules for Cadential 6/4 Chords

To ensure smooth voice leading:

  1. Bass: Stays on sol (5th scale degree) from I⁶₄ → V.
  2. Upper Voices:
    • Do (1st scale degree) → ti (7th scale degree)
    • Mi (3rd scale degree) → re (2nd scale degree)
    • Sol (5th scale degree) remains or moves to the root of V.

Common Mistakes to Avoid

  • Parallel 5ths/Octaves – Check between I⁶₄ and V.
  • Doubling the Bass Incorrectly – Avoid doubling the 5th in the I⁶₄ chord.
  • Resolving the 6/4 to a Non-Dominant Chord – It must go to V (or V7).

Why Is the Cadential 6/4 Important in AP Music Theory?

  • Strengthens the Cadence – Creates a dramatic pause before resolution.
  • Common in Classical Music – Used by Mozart, Beethoven, and Bach.
  • Frequently Tested – AP Music Theory exams often include analysis questions on 6/4 chords.

Practice Example

Chord Progression:
I – IV – I⁶₄ – V – I

In C Major:
C (I) – F (IV) – C/E-G (I⁶₄) – G (V) – C (I)

Try Analyzing:

  • Where is the cadential 6/4?
  • How does the bass move?
  • Are the upper voices resolving correctly?

Final Tips for Mastering Cadential 6/4 Chords

✅ Listen to Examples – Haydn and Mozart frequently use this progression.
✅ Practice Writing Them – Compose short progressions using I⁶₄ → V → I.
✅ Memorize the Resolution – Do → Ti, Mi → Re, Sol → (Sol or Do).


Conclusion

The Cadential 6/4 chord is a crucial concept in AP Music Theory, enhancing harmonic tension before a dominant resolution. By understanding its structure, function, and voice-leading rules, you’ll be well-prepared for exam questions and musical analysis.

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