6th-string-root shell set — Maj7·7·m7 with three fingers

Yesterday you dieted G7 into a shell (R·b7·3). Today you build a set of 6th-string-root shells. The root stays on the 6th string, and the two inner strings are each a switch:

• 4th string = the 7th switch. Fret 4 (7, Maj7) ↔ fret 3 (b7, dominant/minor 7).
• 3rd string = the 3rd switch. Fret 4 (3, major) ↔ fret 3 (b3, minor).

The combination of these two strings gives all three characters:

• Gmaj7 shell = 4th string 4 (7) · 3rd string 4 (3)
• G7 shell = 4th string 3 (b7) · 3rd string 4 (3)
• Gm7 shell = 4th string 3 (b7) · 3rd string 3 (b3)

The two switches (3rd & 7th) you've used for three weeks are alive in the shell too. It's just that with no 5th or doubled note, you now operate only the two remaining color notes clearly. Looks complicated? But there are only two things to remember — the "7th string" and the "3rd string." Get these two switches into your hands and you can flip between major, dominant, and minor with a single finger. You're not memorizing three chords; you're learning two switches.

Three 6th-string-root shells. Green is the 3rd & 7th; move just two strings and the character changes.

Example 1 — two-switch check line. 4th string 7↔b7, 3rd string 3↔b3. Hear how the color notes change on the two strings.

▶ BPM 72. 4th string (7→b7), 3rd string (3→b3). Learn the motion of the two color notes. Repeat 4×.

Example 2 — shell-set cycle comp. Gmaj7 → G7 → Gm7. The root (6th) stays fixed; only the 4th and 3rd strings change.

▶ BPM 78, repeat 4×. Gmaj7 → G7 → Gm7. The root stays; only the two color notes move inside. Hear the three characters clearly distinct.

0–10 min · Warm-up Play the Gmaj7 → G7 → Gm7 shells in order, four beats each. Root (6th) fixed, 5·2·1 muted, only 4·3 moving.

10–20 min · Brain training (today's target = the two color notes) With Example 1, confirm the 4th-string (7/b7) and 3rd-string (3/b3) positions. Eyes closed, on "Gm7!" both strings jump straight to fret 3.

20–40 min · Real comping (Example 2 cycle / 74–84 BPM) Repeat Example 2 at BPM 78 4×. Then move just the root to another fret (e.g., A = fret 5) and apply the same set. Get used to the thin, fast shell comp.

40–50 min · Record & reflect (recommended) Record 30 seconds of the three-shell cycle. Check: do dropped strings stay silent, are the three characters distinct, are the changes fast?

Done when: with a 6th-string-root shell, you can cycle Gmaj7·G7·Gm7 using only the 4th and 3rd strings while the root stays fixed.

• Keep lifting the root. The 6th-string root is fixed. Move only the 4th and 3rd.
• Confusing 7th and 3rd. The 4th string is the 7th, the 3rd string is the 3rd. Upper (4th) = seven, lower (3rd) = third.
• Dropped strings leaking. Cover the 5·2·1 firmly with finger flesh.
• Memorizing the shell as a shape. Think "root + 7th (4th) + 3rd (3rd)." Knowing the identity makes it work on the 5th-string root too (tomorrow).