Tritone Substitution

ii–♭II7–I — same shell, new chord name, chromatic bass

Take the V7's shell — the 3rd and the ♭7th. Those exact two pitches are also the ♭7th and 3rd of the chord a tritone away. So you can re-label any V7 as a ♭II7 and the shell voicing doesn't move: the roles of "3" and "♭7" swap, the chord name and bass note change, your hand stays still.

What you gain is a chromatic bass line — ii → ♭II → I descends by half step at every move, instead of jumping fourths. The voice-leading economy is identical to the original shell exercise; the harmonic flavour is darker.

Shell stays

The two notes don't move; their roles flip (3 ↔ ♭7).

Bass walks

Root motion descends by half step: ii → ♭II → I.

C major

F major

B♭ major

E♭ major

A♭ major

D♭ major

G♭ major

B major

E major

A major

D major

G major

The Daily Drill

Hear the descent

3 minAlternate one bar of plain ii–V–I, one bar of ii–♭II–I, in the same key. The shell doesn't move; only the bass note does. That's the whole pedagogy in five seconds.
10 minCycle four keys at a time. Sing the bass line out loud — chromatic motion is half the point.
4 minPick a tune with a turnaround (Take The A Train, Satin Doll) and substitute ♭II7 for V7 in the last bar. Listen to it open up.
3 minMix freely: alternate V7 and ♭II7 within a single phrase. You're already there harmonically.

About the spelling

When the ♭II7 lands on a key whose proper spelling is a double-flat (e.g. B♭♭7 in A♭), we use the practical enharmonic (A7 here) so the chord name is something a band would actually call. The shell pitches are unchanged; only the upper-voice spelling flips to match the substitute's own scale.

Same two notes, new gravity. Tritone subs are the cheapest reharm in jazz — the door is already open.

80 bpm

Sound