The major third on 7-string guitar

A major third is four semitones, from C to E. Inverted, with the lower note moved up an octave, it becomes the minor sixth.

Its short name is M3. Counted in letters, it spans three letter names, which is why it is written C to E rather than with another name for the same pitch.

On 7-string guitar, the major third is one fret back and the same fret when you cross to the next string, and four frets up along one string.

One pair of neighboring 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, and it moves every shape that crosses the gap, including the ones that skip a string.

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

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

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

20 notes are marked across seven strings.

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

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

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.

Seven chord types contain a major third: Major, Augmented, Major 7th, Dominant 7th, Dominant 9th, Dominant 13th, Augmented major 7th.

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