The Key of F at the Piano Seat

Called in F, a tune has F – Gm – Am – Bb – C – Dm – E° available to it before anybody substitutes anything; the parallel minor, F minor, offers Fm – G° – Ab – Bbm – Cm – Db – Eb instead. The two-five-one that closes most choruses is built out of three of those seven.

The piano seat carries the whole harmony at once — a shell in the left hand, the colour tones and any substitution in the right, which is why this is the seat a substitution is usually heard from first. It is the only seat here that can state a chord and its substitute in the same beat, left hand holding one and right hand implying the other.

Learn where the ii, the V and the I fall in F until the hand goes there without asking, and the substitution rules become edits to something you already know rather than new material.