Major Sixth

Count letter names from C to A, including both ends: C, D, E, F, G, A. That makes it a sixth.

Count the keyboard distance and you find nine semitones. That size makes it major.

C to A flat still spans six letter names but covers eight semitones, so it is a minor sixth. C to A sharp covers ten semitones and is an augmented sixth in the right written context.

Invert C-A by moving C above A. The new interval is A-C, a minor third.

Interval numbers add to nine under inversion: 6 plus 3. Major quality becomes minor, so a major sixth inverts to a minor third.

The same pair of pitch classes can therefore serve different roles. With C below A, measure a major sixth. With A below C, measure a minor third.

A is degree 6 of the C major scale, so C to A is a major sixth.

Every major scale has a major sixth above its tonic. In G major it is G-E; in F major it is F-D.

Natural minor has a minor sixth above the root. A natural minor uses F, eight semitones above A. Dorian and melodic minor use a major sixth above their minor tonic, which helps distinguish them from natural minor.

C6 contains C-E-G-A. The A is a major sixth above the root and is added to a C major triad.

Cm6 contains C-E flat-G-A. The chord is minor because of E flat, while A remains a major sixth above C.

The symbol m6 means minor triad plus major sixth. It does not mean add a minor sixth. C minor with A flat would need a different symbol and harmonic explanation.

Voicing changes the audible result. Place A directly beside G and the notes form a major second; put A higher and the added color becomes more open.

C6 and Am7 contain the same four pitch classes:

The chord name depends on which note functions as root. A C bass and C-centered progression support C6. An A bass and A-minor function support Am7.

Pitch content alone does not always settle chord identity. Bass, phrase position and harmonic motion matter.

An ascending major sixth moves nine semitones upward, such as C4 to A4. A descending major sixth reverses that motion, such as A4 to C4.

Wide leaps are often balanced by stepwise motion afterward, but this is a melodic tendency rather than a rule.

Practice the interval over a root drone and without one. The drone makes C sound like the reference; hearing the two notes alone trains the distance itself.

A minor sixth is one semitone narrower. Compare C-A with C-A flat from the same root.

A minor seventh is one semitone wider. Compare C-A with C-B flat.

Inside a chord, the upper note may be heard as scale degree 6 or as part of another chord inversion. Identify the bass and root before deciding what the interval means harmonically.

A pure major sixth can use the frequency ratio 5:3, about 884 cents.

Equal temperament places nine semitones at 900 cents, about sixteen cents wider. A piano keeps that fixed size in every key.

Singers and string players can adjust a sustained sixth slightly when blending a chord. The interval name remains major sixth; the tuning version changes.