The Key of E at the Piano Seat

Called in E, a tune has E – F#m – G#m – A – B – C#m – D#° available to it before anybody substitutes anything; the parallel minor, E minor, offers Em – F#° – G – Am – Bm – C – D 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 E until the hand goes there without asking, and the substitution rules become edits to something you already know rather than new material.