The major seventh on 7-string guitar

A major seventh is eleven semitones, from C to B. Inverted, with the lower note moved up an octave, it becomes the minor second.

Its short name is M7. Counted in letters, it spans seven letter names, which is why it is written C to B rather than with another name for the same pitch.

On 7-string guitar, the major seventh is six frets up and seven frets up when you cross to the next string, and eleven frets up along one string.

One pair of strings is the odd one out, because the gap between those two strings is different from the rest. Most players learn that exception as a rule of its own.

On a treble staff, the two notes are written C and B.

The staff shows the two notes one after the other, then together. C to B spans seven letter names, which is what the interval's name counts. What you hear is a distance of eleven semitones.

A keyboard makes this distance easy to see, where a fretboard hides it. The upper note is eleven keys along from the lower one, counting black and white keys alike.

30 notes are marked across seven strings.

This diagram marks both notes of the major seventh, C and B, everywhere they fall on 7-string guitar. You can find every pair shown above somewhere on it.

C–B, D♭–C, D–C♯, E♭–D, E–D♯, F–E, F♯–E♯, G–F♯, A♭–G, A–G♯, B♭–A, B–A♯

The shapes above do not change with the key, which is the reason to learn an interval as a shape. Only the note names change, and this table gives them for every starting note.

Three chord types contain a major seventh: Major 7th, Minor-major 7th, Augmented major 7th.

These are the chords with a major seventh above their root. A chord is built by stacking intervals on a root, and a triad is the simplest case, with two of them.