Jazz isn't a style as much as a vocabulary built on top of standard tonal harmony. Take a pop progression, add 7ths (and 9ths, 11ths, 13ths), substitute dominants for tritone subs, insert ii-Vs before key chords, and add secondary dominants — and a 4-chord song becomes a jazz standard.

What jazz adds

• Extensions (7, 9, 11, 13) on every chord
• ii-V-I as the basic motion
• Secondary dominants tonicizing each diatonic chord
• Modal interchange and modal vamps
• Tritone subs for chromatic bass motion
• Improvisation as the centerpiece, not a solo break

Where to go next

Learn 'Autumn Leaves' (a perfect intro to jazz changes), then 'All The Things You Are' (modulating ii-V-Is), then 'Giant Steps' (Coltrane's harmonic puzzle). Practice ii-V-I in all 12 keys. Listen to as much as you play.