The minor third on bass

A minor third is three semitones, from C to E♭. Inverted, with the lower note moved up an octave, it becomes the major 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 bass, the minor third is two frets back when you cross to the next string, and three frets up along one string.

Every pair of neighbouring strings gives the same shape, because the strings of this tuning are evenly spaced. Once you have learned the shape, it works anywhere on the neck.

On a bass 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 three semitones.

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

14 notes are marked across four strings.

This diagram marks both notes of the minor third, C and E♭, everywhere they fall on bass. 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.

Six chord types contain a minor third: Minor, Diminished, Minor 7th, Half-diminished, Diminished 7th, Minor-major 7th.

These are the chords with a minor 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.