Lesson: Borrowed Chords

What key am I in? That chord is not in this key! What scale do I play over this chord? I've had to ask myself that question on a number of occasions. Sometimes chord progressions, or shall we say, songs, do not follow the rules of diatonic harmony. Usually you can analyze what is happening with the chords if you consider something old, new, borrowed, or blue. Let's take a look at relative and parallel keys.