Relative keys share notes with a different tonic; parallel keys share a tonic with different notes, and swapping between parallels is modal interchange

Two keys relate in two distinct ways. Relative keys share the same notes but have a different tonic — A minor is the relative minor of C major (same seven notes, tonic moved). Parallel keys share the same tonic but differ in their notes — A major and A minor are parallel (same tonic ‘a’, different scale). Borrowing a chord from the parallel mode mid-track — playing an A-minor chord inside an A-major passage — is modal interchange, a way to inject a contrasting harmonic color without changing key. Distinguishing relative from parallel is prerequisite to using modal interchange deliberately rather than by accident.

Examples

C major ↔ A minor: relative (same notes). A major ↔ A minor: parallel (same tonic). Borrowing the bVI chord from A minor into an A-major progression = modal interchange.

Assessment

State the difference between relative and parallel keys with an example of each. Explain what modal interchange borrows and from where.