Music Theory and AI

Paul Gauguin: “The Guitar Player” 1894

I learned these things from Claude and ChatGPT about music theory:

Understanding Chords

"major-minor" seventh chords!

A major-minor seventh chord (often called a "dominant seventh chord") is a four-note chord that combines:

1. A major triad (root, major third, perfect fifth)
2. A minor seventh interval above the root

For example, a G major-minor seventh chord (written as G7) contains:

• G (the root)
• B (major third)
• D (perfect fifth)
• F (minor seventh)

This specific chord structure creates a characteristic tension that strongly wants to resolve, typically to a chord whose root is a perfect fifth below (or a perfect fourth above). This is why G7 naturally wants to resolve to C.

The major-minor seventh chord is called "dominant seventh" because it's built on the fifth degree (dominant) of a major scale. It's one of the most important chords in tonal music and is written simply with the root note followed by "7" (like C7, F#7, Bb7).

This chord is different from a major seventh chord (Cmaj7, which has a major seventh) or a minor seventh chord (Cm7, which has a minor third and minor seventh).

Tonic and Dominant

Let me explain what "built on the fifth degree" means.

In music theory, a scale has different "degrees" or positions. Each note in the scale is numbered from 1 to 7 (or using Roman numerals I through VII). The first note of the scale is called the "tonic" or first degree.

When we say a chord is "built on" a particular degree, we mean that the root note of the chord is that specific scale degree.

For example, in the key of C major (C-D-E-F-G-A-B-C):

• C is the 1st degree (I) - the tonic
• D is the 2nd degree (II)
• E is the 3rd degree (III)
• F is the 4th degree (IV)
• G is the 5th degree (V) - the dominant
• A is the 6th degree (VI)
• B is the 7th degree (VII)

The 5th degree (G in this case) is called the "dominant." When we build a chord using G as the root and follow the pattern of the major scale, we naturally get a major-minor seventh chord:

• G (root)
• B (major 3rd)
• D (perfect 5th)
• F (minor 7th)

This G7 chord is "built on" the fifth degree of C major. The dominant seventh chord occurs naturally when you build a seventh chord on the fifth degree of any major scale. This is why it's called the "dominant seventh" - it's the seventh chord built on the dominant (fifth) degree.

This relationship between the tonic (C) and dominant (G) creates the fundamental tension and resolution pattern in tonal music, which is why the dominant seventh chord is so important.

Minor Major Chord

You're thinking of the minor-major seventh chord!

This is the chord that creates that distinctive "eerie," "mysterious," or "unresolved" quality that jazz guitarists often use for endings. It's particularly common in noir jazz, film scores, and those TV show moments that leave you hanging with questions.

A minor-major seventh chord consists of:

• A minor triad (root, minor third, perfect fifth)
• Plus a major seventh interval above the root

For example, a C minor-major seventh chord (written as CmM7, Cm(maj7), or Cmin/maj7) contains:

• C (the root)
• E♭ (minor third)
• G (perfect fifth)
• B (major seventh)

This unusual combination creates a haunting, ambiguous sound that feels simultaneously dark (because of the minor triad) yet sophisticated and tense (because of the major seventh). It's perfect for creating that "question mark" feeling at the end of a scene or piece.

This chord appears naturally in the melodic minor scale and is used extensively in jazz, film music, and other styles that want to evoke mystery or leave things intentionally unresolved.

13th and 10th Chords

In music, the 13th of an "A" refers to a 13th interval built from the note A.

A 13th interval spans 13 scale degrees, which is equivalent to an octave plus a 6th. So the 13th of A would be F♯ (F-sharp) in the key of A major, or F in the key of A minor.

To break it down:

• Start with A
• Count up 13 scale degrees (or think of it as going up an octave to A and then up to the 6th note from there)
• In A major: A → B → C♯ → D → E → F♯ → G♯ → A → B → C♯ → D → E → F♯
• In A minor: A → B → C → D → E → F → G → A → B → C → D → E → F

So the 13th of A is F♯ in a major context or F in a minor context. 

In music, the 10th of "A" refers to a 10th interval built from the note A.

A 10th interval spans 10 scale degrees, which is equivalent to an octave plus a 3rd. So the 10th of A would be C♯ (C-sharp) in the key of A major, or C in the key of A minor.

To break it down:

• Start with A
• Count up 10 scale degrees (or think of it as going up an octave to A and then up to the 3rd note from there)
• In A major: A → B → C♯ → D → E → F♯ → G♯ → A → B → C♯
• In A minor: A → B → C → D → E → F → G → A → B → C

So the 10th of A is C♯ in a major context or C in a minor context.