What it is
Seven notes, spaced like this from the root: W W H W W W H, where W is a whole step (two frets) and H is a half step (one fret). On bass you usually play it as a two-octave shape across four strings.
Starting on the E string, fret 3 (G major), the shape is:
G string: 5 7
D string: 4 5 7
A string: 3 5 7
E string: 3 5 7
Same shape works from any root — just shift.
Why it matters
The major scale is the ruler everything else is measured against. Chords get named by where their notes sit relative to it (a minor 3rd is minor because it is a half-step lower than the major scale's 3rd, etc.). You cannot get far in theory without this shape in your hands.
How to practice
- Play the shape ascending and descending. Slow.
- Open it in the fretboard explorer and walk the shape. Turn on Advanced to try other roots and see the same shape move.
- Sing the scale as you play it. "Do re mi fa sol la ti do." Ear training comes free.