Now, as we were saying, since the key of C has no flats or sharps, any chord that contains any flat or sharp is not actually part of the key of C. Where did it come from?
What music theory tries to do is to look at these chords in terms of how they fit into the flow of the chord progression. All chord progressions are simply movements from one point to the next, hopefully they will eventually bring us back to the home (or root) chord. Sometimes in moving from one point to the next, we are actually “borrowing” chords from other keys (here the Bb in #1, the E7 and D7 in #2 and the A and D in #3). Theory tries to label these chords in terms of the keys from which they are borrowed. We (usually) try to determine where they came from by where they are going to (how they are resolved).
Related Questions
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